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Gaseous Patients
removes rectal gas

ImmobiLoc® patented gas-release tip allows transient rectal gas to be evacuated from the rectum, reducing prostate motion.

Post Radical Patients
defines anatomy

ImmobiLoc® provides reproducible positioning of the rectum for difficult planning scenarios.

Low Bowel Patients
lifts low lying bowels

ImmobiLoc® is used as a positioning device for the rectum and adjacent structures during external beam radiation therapy for prostate cancer.

Intrafractional Motion
ImmobiLoc® limits internal motion during beam delivery
Dancing Prostate

This video demonstrates the significant motion during treatment of the prostate, rectum, and bladder when a gas-release endorectal balloon is absent.

Interfractional Changes
ImmobiLoc® provides reproducible setup for daily treatments

The following 23 consecutive CT images demonstrate significant changes in rectal volume, size and shape of the prostate, rectum and bladder when the ImmobiLoc® Endorectal Balloon is absent.



The following two CT images are frame grabs showing bladder in blue, prostate in green and rectum in yellow demonstrate significant changes in size and shape when the ImmobiLoc® is absent.

CT Scan 2CT Scan 18


Transient rectal gas can change the volume and the shape of the rectum and prostate making consistent treatment setup challenging.

Simulation and TreatmentSimulation and Treatment

These images reflect consistent daily setup when the ImmobiLoc® Endorectal Balloon is used.

for patient comfort

Provides the smallest diameter and most flexible shaft for superior patient comfort.

The Preferred ERB
for all treatment modalities

"Prostate image-guided-IMRT using a daily ImmobiLoc® shows low rates of acute GI toxicity compared to published studies when using strict infield rectum DVH constraints"

C. Deville, S. Both, W. Hwang, M. Schaer, V. Bui, J. Bekelman, J. Christodouleas, Z. Tochner, N. Vapiwala University of Pennsylvania Medical Center, Philadelphia, PA, Radiation Oncology 2012 7:76

Clinical Library Clinical Studies

Emerging Evidence for the Role of an Endorectal Balloon in Prostate Radiation Therapy
Stefan Both, Curtiland Deville, Viet Bui, Ken Kang-Hsin Wang, Neha Vapiwala, University of Pennsylvania, Philadelphia, PA, Transl Cancer Res 2012;1(3):227-235

Purpose: To reassess and update the role of an endorectal balloon (ERB) in prostate radiotherapy (RT) based on emerging evidence by reviewing various aspects of treatment methodologies and clinical outcomes.

Materials/Methods: A literature review based on a PubMed/MEDLINE database search using keywords such as: ERB, prostate RT, toxicities, real-time, image-guided radiotherapy (IGRT), radiofrequency-guided radiotherapy (RGRT), and inter- and intrafraction prostate motion for articles published over the past two years. Ten articles were identified and subdivided into three categories: (I) Issue of Motion, (II) Dosimetry, (III) Clinical Outcomes.

Results: With the advent of real-time prostate tracking, analysis of intrafraction motion as a function of treatment time for patients treated with a daily-ERB was performed and revealed an overall reduction in 3D prostate motion, especially in the anterior-posterior direction. Two different groups of authors found that this reduction in intrafraction prostate motion allowed for tighter internal margins. Dosimetric studies showed overall improved dose distributions which for proton therapy were maximized when using ERB-guided range verification for anteriorly oriented beams. Clinical outcomes showed favorable early GI toxicities however late toxicity results are still awaited.

Conclusions: Utilizing a daily-ERB shows favorable early GI toxicity as well as reduced prostate intrafraction motion based on real-time tracking data. Reduced intrafraction motion improves the feasibility to use anteriorly oriented proton beams, which may further improve dosimetry.

Comprehensive Study On Real-Time Prostate Gland Motion Between Patient Groups Undergoing Radiotherapy With And Without Daily Endorectal Balloon
K. Wang, N. Vapiwala, R. Scheuermann, J. Plastaras, V. Bar Ad, Z. Tochner, S. Both. et al., Department of Radiation Oncology, University of Pennsylvania, Philadelphia, PA, Int. J. Radiat Oncol Biol Phys, Nov 2010; 78 Issue 3; Supplement PS683-S684

Purpose: The aim of this study is to quantify the differences in real-time prostate motion between undergoing radiotherapy with and without daily ERB.

Materials/Methods: More than 600 treatment sessions were analyzed for each patient group. We first analyzed the overall 3D motion of the prostate, which is calculated as the absolute excursion of the prostate with respect to its initial position. The analysis was carried out by calculating the average percentage time that the prostate moves . 2, 3, 4, 5, 6, 7, and 8 mm within 1 minute intervals over 6 minutes of treatment time. We further studied the prostate motion in the left-right, cranial-caudal, and anterior-posterior direction. A two-sample Kolmogorov-Smirnov test is chosen to evaluate the pattern of the prostate motion . 2, 3, 4, 5, 6, 7, and 8 mm for the non-ERB and ERB group.

Results: Our results clearly state that the percentage time and the magnitude of the 3D prostate motion is higher for the non- ERB group compared to the ERB group, i.e., 6% vs. 0.4% of time that the prostate had motion of .5 mm for the non-balloon and balloon group, respectively. The prostate displacement for the non-ERB group is larger comparative to that of the balloon group at any time. Differences of the prostate motion between the non- and balloon group are found in the cranial-caudal (up to 5% time difference) and especially in the anterior-posterior direction (up to 13% time difference). Our results show that the effectiveness of ERB in reducing the anterior-posterior motion is increased along with treatment time; within the 6th minute treatment time, the percentage time of prostate motion . 2 and . 5 mm had been reduced from 24% to 12% and 3.2% to 0%, respectively, between these two groups. Our statistic tests show that in terms of the 3D prostate excursion, the motion pattern between these two groups becomes significantly different (p \ 0.05) when the prostate displacement is . 5, 6, 7, and 8 mm.

Conclusions: In summary, our results suggest that daily ERB has great impact on reducing large intrafraction prostate motion (>5mm), and demonstrate significantly different prostate motion patterns during therapy for patients treated with and without ERB.

Real-Time Study Of Prostate Intrafraction Motion During External Beam Radiotherapy With Daily Endorectal Balloon
Stefan Both, Ph.D., Ken Kang-hsin Wang, Ph.D., John P. Plastaras, M.D., Ph.D., Curtiland Deville, M.D., Voika Bar Ad, M.D., Zelig Tochner, M.D., and Neha Vapiwala, M.D. Int. J. Radiation Oncology Biol. Phys., Vol. 81, No. 5, pp. 1302–1309, 2011

Purpose: To prospectively investigate intrafraction prostate motion during radiofrequency-guided prostate radiotherapy with implanted electromagnetic transponders when daily endorectal balloon (ERB) is used.

Materials/Methods: Intrafraction prostate motion from 24 patients in 787 treatment sessions was evaluated based on three-dimensional (3D), lateral, cranial-caudal (CC), and anterior-posterior (AP) displacements. The mean percentage of time with 3D, lateral, CC, and AP prostate displacements >2, 3, 4, 5, 6, 7, 8, 9, and 10 mm in 1 minute intervals was calculated for up to 6 minutes of treatment time. Correlation between the mean percentage time with 3D prostate displacement >3 mm vs. treatment week was investigated.

Results: The percentage of time with 3D prostate movement >2, 3, and 4mmincreased with elapsed treatment time (p < 0.05). Prostate movement >5 mm was independent of elapsed treatment time (p = 0.11). The overall mean time with prostate excursions >3 mm was 5%. Directional analysis showed negligible lateral prostate motion; AP and CC motion were comparable. The fraction of time with 3D prostate movement >3mmdid not depend on treatment week of (p > 0.05) over a 4-minute mean treatment time.

Conclusions: Daily endorectal balloon consistently stabilizes the prostate, preventing clinically significant displacement (>5 mm). A 3-mm internal margin may sufficiently account for 95% of intrafraction prostate movement for up to 6 minutes of treatment time. Directional analysis suggests that the lateral internal margin could be further reduced to 2 mm.

A Study To Quantify The Effectiveness Of Daily Endorectal Balloon For Prostate Intrafraction Motion Management
KKH Wang, N. Vapiwala, C. Deville, J. Plastaras, R. Scheuermann, H. Lin, V Bar Ad, Z Tochner, and S.Both, et al., Int. J. Radiat Oncol Biol Phys, 2011 in-press

Purpose: To quantify intrafraction prostate motion between patient groups treated with and without daily endorectal balloon (ERB) employed during prostate radiotherapy and establish the effectiveness of the ERB.

Materials/Methods: Real-time intrafraction prostate motion from 29 non-ERB (1,061 sessions) and 30 ERB (1,008 sessions) patients was evaluated based on three-dimensional (3D), left, right, cranial, caudal, anterior, and posterior displacements. The average percentage of time with 3D and unidirectional prostate displacements >2, 3, 4, 5, 6, 7, 8, 9, and 10 mm in 1-min intervals was calculated for up to 6 min of treatment time. The Kolmogorov-Smirnov method was used to evaluate the intrafraction prostate motion pattern between both groups.

Results: Large 3D motion (up to 1 cm or more) was only observed in the non-ERB group. The motion increased as a function of elapsed time for displacements >2e8 mm for the non-ERB group and >2e4 mm for the ERB group (p < 0.05). The percentage time distributions between the two groups were significantly different for motion >5 mm (p < 0.05). The 3D symmetrical internal margin (IM) can be reduced from 5 to 3 mm (40% reduction), whereas the asymmetrical IM can be reduced from 3 to 2 mm (33% reduction) in cranial, caudal, anterior, and posterior for 6 min of treatment, when ERB is used. Beyond 6 min, the symmetrical 3D and asymmetrical cranial, caudal, anterior, and posterior IMs can be reduced from 9, 4, 7, 7, and 8 to 5, 2, 5, 3, and 4 mm, respectively (up to 57% reduction).

Conclusions: The percentage of the time the prostate displaces in any direction is overall less in the ERB group than the non-ERB group. The symmetrical #D IM can be reduced from 5 to 3 mm (40%) reduction to cover 95% of 6 min treatment time, if the ERB is employed. In the cranial, caudal, anterior, and posterior direction, 2-mm IM should be used for the ERB group along each axis, and 3-mm IM can be used for the non-ERB group.

First Prospective Study To Determine The Role Of Daily Endorectal Balloon On Prostate Intrafraction Motion Management During External Beam Radiotherapy
S. Both, K. Wang, J. Plastaras, C. Deville, V. Bar Ad, Z. Tochner, N. Vapiwala et al., Radiation Oncology, University of Pennsylvania, Philadelphia, PA, Int. J. Radiat Oncl Bio Phys, October 2010; Supplement PS6669

Purpose/Objective(s): Highly conformal prostate RT techniques mandate accurate and reproducible target localization. Variations in rectal filling with gas and/or stool contribute to inter- and intrafraction target motion within the pelvis may be critical. Daily endorectal balloon (ERB) is one strategy for prostate immobilization and has the potential to reduce rectal toxicity. Radiofrequency- guided RT (RGRT) with implanted electromagnetic transponders is available for daily prostate isocenter localization and tracking. RGRT was used to investigate the impact of ERB on stabilizing intrafraction prostate motion and minimizing changes in motion pattern over the course of radiation therapy.

Materials/Methods: Raw tracking data from 24 patients (836 sessions) was exported and analyzed to evaluate prostate motion during each fraction. Intrafraction motion was evaluated based on 3D displacement, calculated as the absolute displacement of the prostate with respect to its initial position. We further quantified prostate motion in each direction (lateral x, cranial-caudal y, and anterior-posterior z) in order to differentiate the impact of ERB. For each analysis (3D, x, y, and, z), we calculated the average percentage of time that the prostate moves more than 2, 3, 4, 5, 6, 7, 8, 9, and 10 mm within 1 minute intervals over all of the available sessions. To evaluate the prostate displacement as a function of treatment weeks, we performed a correlation study between the average percentage of time the prostate spent at 3D displacement of .3 mm vs. week of treatment.

Results: The 3D prostate motion increases along with treatment time in the case of.2 and 3mmdisplacements, while it is less time dependent for all other cases. We observe that movements more than 6mmfor all of the cases considered occur less than 0.6% time. Our correlation analysis shows that percentage of time for prostate movement . 3 mm increases throughout treatment (p\0.01), while the prostate movement . 5 mm is independent of the treatment time (p = 0.1). The directional analysis shows that the percentage of time of lateral prostate motion is negligible and that prostate intrafraction motion in the cranial-caudal and anterior- posterior directions become comparable as a consequence of using daily ERB. The fraction of time the prostate movement .3 mm does not depend on the week of treatment (p . 0.05) within the average treatment times of rapid arc (2 min) and IMRT (4 min) techniques.

Conclusions: The results show that the ERB consistently stabilizes prostate displacement (.5 mm) within the analyzed treatment time (6 min) and the dynamic of prostate motion (.3 mm) is not changing over the treatment course.

Is Prostate Inter- And Intrafraction Motion Dependent On Stool/Gas Volume Changes For Patients Undergoing Radiotherapy With Daily Endorectal Balloon?
K. Wang, N. Vapiwala, C. Deville, J.P. Plastaras, V. Bui, V. Bar Ad, Z. Tochner, S. Both et al., University of Pennsylvania, Philadelphia, PA, Jefferson University, Philadelphia, PA, Int. J. Radiat Oncol Biol Phys, Vol 81 Issue 2; Supplement PS444, October 2011

Purpose:Highly conformal prostate radiotherapy (RT) techniques mandate accurate and reproducible target localization. Daily variations in rectal filling with gas and/or stool may contribute to inter- and intrafraction prostate motion during RT. We investigate the impact of these variations on prostate motion during RT with daily endorectal balloon (ERB).

Materials/Methods: Thirty patients undergoing prostate RT with daily ERB, radiofrequency-guided RT, and weekly CBCTwere prospectively enrolled on this IRB-approved study at the Hospital of the University of Pennsylvania. The ERB with indexed lumen was inserted into rectum and filled with 100mL of water. A total of 197 treatment sessions were used to analyze the impact of stool/gas volume variability on prostate displacement over the RT course. The corresponding tracking data was evaluated for initial prostate localization and intrafraction motion during each treatment session, based on 3D, lateral (L), cranial-caudal (CC), and anterior-posterior (AP) displacements. For intrafraction motion, the average prostate motion within 1 minute intervals for up to 6 minutes of treatment time was calculated. For the correlation analysis of stool/gas volume with motion, patients were classified into two groups: small (\15 cc) vs. large volume ($ 15 cc).

Results: The magnitude of prostate intrafraction in 3D, L, CC, and AP directions increased with elapsed treatment time (p\0.05). However, for both the small and large stool/gas volume groups, no consistent pattern of intrafraction motion correlated to the volume in any of the directions during the analyzed treatment time (p.0.05). In terms of interfraction motion, no significant correlation between the initial localization uncertainty and stool/gas volume were demonstrated in this study (p.0.05).

Conclusions: Our preliminary analysis suggests that stool/gas volume variability during prostate RT may not impact inter- or intrafraction prostate motion when a daily ERB is employed. This study renders that with ERB, stool/gas variations may be inconsequential to the treatment outcome.

Reduction Of Prostate Intrafraction Motion Using Gas-Release Rectal Balloons
Z. Su, T. Zhao, Z. Li, B. Hoppe, R. Henderson, W. Mendenhall, C. Nichols, R. Marcus, N. Mendenhall et al.
University of Florida Proton Therapy Institute, Jacksonville, FL Int. J. Radiat Oncol. Bio Phys, Vol 81 Issue 2; Supplement PS780, October 2011

Purpose: Gas release (GR) rectal balloons allow bowel gas transiently pass through during patient treatments. This may reduce intrafractional prostate motion uncertainties in the treatment of prostate cancer compared with non-gas release (NGR) balloons. The present study evaluates the magnitude of prostate intrafractional motion between patients using NGR and GR balloons and assesses required margins to ensure coverage of the prostate.

Materials/Methods: From all prostate patients received proton therapy at the University of Florida Proton Therapy Institute, 108 patients were random selected for this study and included 59 who had NGR and 59 who had GR balloons. These patients were setup using implanted markers on a 6D couch. Each patient had pre-treatment and post-treatment orthogonal 2D x-ray radiographs for treatment setup and intrafractional motion evaluation, respectively. The pre-treatment setup residual error was maximum 2mm in each axis. The difference between post- and pre-treatment marker position was caused by prostate intrafractional motion. Population histograms of infraction motion and frequencies of prostate deviation from the original setup position were obtained for each axis. The systematic (SIGMA) and random components (sigma) of setup residual and intrafractional motion error were calculated for both types of balloons. Margins to account for residual setup error and intrafractional motion error, were calculated using formula: 2.5*SIGMA+0.7*sigma.

Results: Histograms of intrafractional motion indicated significant reduction of standard deviation by using GR rectal balloon (SI: from 2.1mm to 1.3mm; AP: from 2.8mm to 1.5mm). The maximum magnitude of intrafractional motion was reduced from 8.4 to 6 mm in SI direction and from 9.6 to 7mm in AP direction. Table 1 showed details of intrafractional motion for both types of balloons. The greatest reduction in motion was in the AP and SI directions. The margins to account for intrafractional motion and setup error were 1.9, 4.1, 3.2 mm in LR, SI, AP directions, respectively, for NGR balloon; they were 2.2, 2.8, 2.0 mm in LR, SI, AP directions, respectively, for GR ones.

Conclusions: Intrafraction prostate motion is a dominant source in target geometric and dosimetric uncertainties after daily image guided online correction of interfractional errors. Compared to NGR balloon, GR balloon reduced the magnitude of intrafractional prostate motion in both AP and SI directions. Thus, it led to smaller margins for setup and prostate motion.

In Vivo Dosimetric Verification of Volumetric Modulated Arc Therapy for Prostate Cancer using a Rectal Balloon
J. D. Fontenot, M. Price, M. King Mary Bird Perkins Cancer Center, Baton Rouge, LA, Int. J. Radiat Oncol Biol Phys, Volume 78 , Issue 3 , S819, 2010

Purpose: The use of volumetric modulated arc therapy (VMAT) for prostate cancer is increasing rapidly. As part of patient-specific quality assurance, VMAT plans are verified in phantoms under the assumption that the surrogate geometry appropriately represents the scatter characteristics of the patient. However, for emerging, highly complex treatment delivery techniques, it is desirable to verify treatment delivery in the patient geometry. In this study, we examined an approach for verifying the dose delivered to the high dose volume of prostate patients during VMAT delivery using dosimeters affixed to a rectal balloon.

Materials/Methods: Patient selection was limited to subjects with clinical disease profiles T1-3N0M0. Patients received irradiation to the prostate volume with or without concurrent nodal irradiation. All patients received prostate immobilization during simulation and treatment delivery using the Radiadyne water-filled rectal balloon system. VMAT plans consisting of 1 or 2 350-degree arcs were constructed using the Philips Pinnacle treatment planning system. VMAT plans were delivered using an Elekta Infinity accelerator. Prior to patient positioning, an LiF thermoluminescent dosimeter (TLD) was affixed to the exterior of the rectal balloon. Localization markers were placed 1-cm above and below the TLD along the long axis of the balloon. The balloon was encased in an ultrasound probe cover and inserted into the rectum such that the TLD was oriented along the anterior rectal wall. A daily cone beam CT (CBCT) was acquired and registered to the planning CT. Following treatment, absorbed dose measured by the TLD was compared to the planned dose at the TLD position, which was determined by correlating the position of the localization markers in the CBCT with the planning CT.

Results: VMAT plans provided better than 95% coverage of the planning target coverage for all patients with equal or better sparing of the rectum and bladder compared with a 7-field fixed-beam IMRT plan. The average delivery time for the VMAT plans was 1.8 ± 0.4 minutes. The average measured TLD dose was 191 ± 19 cGy, compared to an average planned dose at the TLD position of 193 ± 15 cGy. The average percent difference between the measured and planned doses was -1.0 ± 5% and did not exceed 7%. Repeat TLD measurements showed intra-patient variations of less than 5%. A subsequent sensitivity analysis revealed that dosimetric results were not sensitive to uncertainties in TLD localization.

Conclusions: Clinical delivery of VMAT for prostate cancer has been verified in vivo using TLDs placed along the anterior rectal wall via immobilization balloon and localized on CBCT. The measurement procedure was valuable clinical tool appropriate for verification of a complex radiation therapy technology.

Acute and Late Toxicity Report of Post-Prostatectomy Proton Therapy for Prostate Cancer Patients Undergoing Adjuvant or Salvage Radiotherapy
Akansha Jain, Neha Vapiwala, MD, Kristina D. Woodhouse, MD, Stefan Both, PhD, Peter Gabriel, MD, Zelig Tochner, MD, Curtiland Deville, MD; 1University of Pennsylvania, 2Memorial Sloan Kettering Cancer Center, Johns Hopkins University, 2017

Purpose: To report the acute and late genitourinary (GU) and gastrointestinal (GI) toxicities associated with post-prostatectomy proton therapy (PT).

Methods: All patients (NZ83) undergoing post-prostatectomy PT on an IRB-approved, institutional protocol from 2010-2015 were assessed. Patients received a median dose of 70.2 Gy relative biological effectiveness (RBE) in 1.8 GyRBE daily fractions using passive scattering (16.9%) or pencil beam scanning technique (83.1%) to the prostate bed (77.1%) or whole pelvis and prostate bed (22.9%). Twenty-seven utilized (32.5%) combined IMRT to achieve predefined dose constraints. Thirty-one patients (37.3%) received concurrent androgen deprivation. Toxicity was scored by CTCAE v4.0. Median follow up was 27 months (range 3e47).

Results: Median age was 64 years (42e77). Median months from surgery were 24 (5e210). Mean pre-op and pre-radiation PSAs were 8.769.06 (1.3e57.6) and 0.631.47 (0.00e8.50), respectively. Pathological tumor stages were T2 (53%), T3 (43)%, T4 (1.2%) and unknown (2.4%). Radical prostatectomy was robotic assisted (66%), retropubic (25%), perineal (7.2%), and unknown (1.2%). Acute and late maximum GU toxicities, respectively were grade 0 (13%; 18%), 1 (64%; 62%), 2 (23%; 20%) Grade two GU toxicities consisted of hematuria and urinary incontinence, retention, urgency, and frequency. Acute and late maximum GI toxicities were respectively, grade 0 (53%; 72%), 1 (43%; 25%), 2 (4%, 3%). All grade 2 GI toxicities consisted of constipation. Median time to maximum GU and GI toxicity was 4 (3-39) and 4 (3-36) months, respectively. The mean baseline International Prostate Symptom Score, International Index of Erectile Function-5, and Expanded Prostate Cancer Index Composite bowel function, and bowel bother scores were 65, 117, 9211, 9315, respectively and after 2 years, the mean scores remained largely unchanged (64, 116, 936, and 9110).

Conclusions: We report the clinical feasibility and favorable acute and late GU and GI toxicity profile of post-prostatectomy PT.

Acute Gastrointestinal and Genitourinary Toxicity of Image-Guided Intensity Modulated Radiation Therapy for Prostate Cancer Using a Daily Water-Filled Endorectal Balloon
Curtiland Deville1,3*, Stefan Both1, Viet Bui1, Wei-Ting Hwang2, Kay-See Tan2, Mattia Schaer1, Zelig Tochner1 and Neha Vapiwala, Deville et al. Radiation Oncology 2012

Purpose: Our purpose was to report acute gastrointestinal (GI) and genitourinary (GU) toxicity rates for prostate cancer patients undergoing image-guided intensity modulated radiation therapy (IG-IMRT) with a daily endorectal water-filled balloon (ERBH2O), and assess associations with planning parameters and pretreatment clinical characteristics.

Materials/Methods: The first 100 patients undergoing prostate and proximal seminal vesicle IG-IMRT with indexed-lumen 100 cc ERBH2O to 79.2 Gy in 1.8 Gy fractions at our institution from 12/2008- 12/2010 were assessed. Pretreatment characteristics, organ-at-risk dose volume histograms, and maximum GU and GI toxicities (CTCAE 3.0) were evaluated. Logistic regression models evaluated univariate association between toxicities and dosimetric parameters, and uni- and multivariate association between toxicities and pretreatment characteristics.

Results: Mean age was 68 (range 51–88). Thirty-two, 49, and 19 patients were low, intermediate, and high-risk, respectively; 40 received concurrent androgen deprivation. No grade 3 or greater toxicities were recorded. Maximum GI toxicity was grade 0, 1, and 2 in 69%, 23%, and 8%, respectively. Infield (defined as 1 cm above/below the CTV) rectal mean/median doses, D75, V30, and V40 and hemorrhoid history were associated with grade 2 GI toxicity (Ps < 0.05). Maximum acute GU toxicity was grade 0, 1, and 2 for 17%, 41%, and 42% of patients, respectively. Infield bladder V20 (P = 0.03) and pretreatment International Prostate Symptom Scale (IPSS) (P = 0.003) were associated with grade 2 GU toxicity.

Conclusions: Prostate IG-IMRT using a daily ERBH2O shows low rates of acute GI toxicity compared to previous reports of air-filled ERB IMRT when using stringent infield rectum constraints and comparable GU toxicities.

Endorectal Balloon In Post-Operative Radiation Therapy For Prostate Cancer
L. K. Morikawa, R. Kudchadker, J. Kanke, M. Oyervides, S. Frank, A. K. Lee, K. Hoffman, S. Choi, Q. Nguyen, D. Kuban et al., MDACC,TX, Int. J. Radiat Oncol Biol Phys, 2010; Vol 78 Issue 3; Supplement PS395

Purpose: Anatomical changes after radical prostatectomy may significantly increase the volume of rectum treated to intermediate and high doses in post-operative radiation therapy (RT). There are no data available on endorectal balloon (EB) use in the post-operative setting. The aim of this study was to investigate the advantage of using EB in prostate cancer patients who undergo post-operative RT and investigate the effects of EB on dose volume histograms (DVH) for the rectum.

Materials/Methods: We retrospectively analyzed 5 patients treated post-operatively for prostate cancer at M.D. Anderson Cancer Center. EB was utilized during CT-based simulation in all patients. Two scans for each patient were generated and identified as scan A (without EB) and scan B (with EB). The same physician contoured scan A and B in all patients. A total of 10 IMRT plans were generated, optimized and approved using scan A and B. DVH analyses of PTV, CTV, V30, V40, V60 and V70 were generated and compared between scan A and B for each patient. Absolute and mean relative dose reduction between each plan was calculated.

Results: EB improved the DVH for the rectum in all patients studied. The PTV and CTV coverage was equivalent in scan A and B. There was a substantial decrease in rectal volumes treated to high doses (60-70Gy) in patients using EB. The relative mean dose reduction to the rectum was: 46.2% for the V70 (range 34-54%); 38.4% for V60 (range 28-47%); 27.6% for V40 (range 13-51%) and 27% for V30 (range 16-51%) in scan B compared with scan A. EB also optimized anatomy in 2 cases: one case of local recurrence located on the anterior rectal wall and another patient with residual seminal vesicles asymmetrically oriented.

Conclusions: EB demonstrated advantage in decreasing the rectum volume treated to doses between 30 and 70Gy in all patients studied. EB may be a useful tool in decreasing the risk of rectal complications in patients irradiated post-operatively and should be considered in post-operative RT. Confirmation of these results in additional patients may help to guide optimal post-operative RT planning and delivery.

Is What You See Really What You Get? Quantification Of Discrepancies Between Planned Vs. Delivered Dose During Prostate Radiotherapy Using Daily Endorectal Balloon
N. Vapiwala, R. Scheuermann, C. Deville, S. Both et al.
University of Pennsylvania Medical Center, Philadelphia, PA. Int. J. Radiat Oncol Biol Phys, October 2009; Supplement PS335

Purpose: This study evaluates the impact of bladder and rectal volume variability on the original planning dose-volume parameters of the target and organs-at-risk (OAR) over a course of prostate radiotherapy (RT) using daily endorectal balloon (ERB) and cone beam CT (CBCT) surveillance. It is the first report to our knowledge to investigate the dosimetric implications of physiological changes in OAR volume as documented with CBCT during prostate RT when daily ERB is employed.

Materials/Methods: We analyzed 70 CBCT datasets coregistered with planning CT’s from 10 patients (pts) undergoing prostate RT with full bladder, daily ERB, and kV orthogonal imaging for localization. Clinical and planning treatment volumes (CTV, PTV), bladder, rectum, and anterior rectal wall (ARW) were contoured on each CBCT dataset. Plans were recalculated for all CBCT’s using a fixed monitor unit method in Eclipse TPS and dose-volume histogram (DVH) parameters were extracted. Percentage differences were calculated between the pt’s planning CT values and average (avg) CBCT values for: bladder/rectal volumes; CTV D98; PTV D95; bladder V45/V65; rectum V40/V60; and ARW V70. Statistical significance of DVH indicators was analyzed using a student t-test. Our institutional prostate regimen is 7-field IMRT to 79.2 Gy with following constraints: CTV D98 $ 79.2 Gy; PTV D95 $ 75.2 Gy; bladder V45 # 50% and V65 #20%; rectum V40 # 50% and V60 #20%.

Results: CTV and PTV coverage were maintained for all pts throughout the entire course of RT. There were statistically significant changes in bladder volume for all pts over the treatment course, with a maximum 8-fold variation between planning CT and avg CBCT volumes (p\0.5). No changes in rectal volume were noted, which we attribute to daily ERB use; rectal V40 and V60 were not statistically significantly different between the original plans and CBCT-based plans. However, ARW V70 showed up to 1.5-fold variation (p\0.5) between planning CT and avg CBCTs. For bladder V45, the planning CT-based and avg CBCT-based values were also statistically significantly different, up to 2-fold higher during RT delivery compared to planning (p\0.5). Interestingly, the differences in bladder V65 were not statistically significant, suggesting minimal variation of the bladder-target interface in the higher-dose regions.

Conclusions: Target coverage and rectal DVH indicators are preserved from prostate RT planning through actual delivery if daily ERB is used. Changes in bladder V45 reflect variable filling and pt compliance over the tx course, possibly as RT-related urinary symptoms develop. ARW dose needs to be monitored and correlated with clinical toxicity to determine its significance.

Initial Report of Acute Gastrointestinal (GI) Toxicity of Image-Guided Intensity Modulated Radiation Therapy (IMRT) for Prostate Cancer using a Daily Water-Filled Endorectal Balloon
C. Deville, S. Both, W. Hwang, M. Schaer, V. Bui, J. Bekelman, J. Christodouleas, Z. Tochner, N. Vapiwala University of Pennsylvania Medical Center, Philadelphia, PA, Radiation Oncology 7:76, 2012

Purpose: Almost three-quarters of prostate cancer foci are present in the peripheral zone in close rectal proximity, but target doses are typically reduced in this region to provide rectal sparing. IMRT for prostate cancer using a water-filled endorectal balloon (ERBH2O), rather than air-filled, should allow for improved target coverage posteriorly. Stricter rectal planning constraints may maintain the anterior rectal wall (ARW) surface-sparing effect and ensure uncompromised rectal sparing while also achieving robust, reproducible coverage. This study reports acute GI toxicity rates using this novel approach and assesses toxicity associations with DVH parameters and patient (pt) characteristics.

Materials/Methods: The first 100 pts undergoing prostate/proximal seminal vesicle IMRT to 79.2 Gy in 1.8 Gy fractions at our institution between 12/2008 - 12/2010 were assessed. All were CT-simulated and treated supine with an indexed-lumen 100 cc ERBH2O. PTV margins involved 1 cm CTVexpansion, except 6 mm posteriorly, with target PTV D95 .95%. Infield (defined as 1 cmabove and below the CTV) rectal constraints included V60\20%, V45\40%, and V40\50%. Pt characteristics, DVHs for rectum (anatomically-defined from sigmoid to anus), infield rectum, ARW, and infield ARW, and maximum CTCAEv4.02 GI toxicities were evaluated. Logistic regression models evaluated associations between grade 2 toxicity and 1) DVH parameters and 2) pt characteristics.

Results: Mean age was 68 (range 51-88). Thirty-two, 49, and 18 pts were low, intermediate, and high-risk, respectively; 40 received concurrent androgen deprivation. Co-morbid hypertension, diabetes mellitus, and hemorrhoid history were present in 72, 47, and 11 pts, respectively. Mean pre- and post-tx Bowel Assessment Scores (BAS) were 20 (13-23) and 19 (11-21). Twelve pts did not meet all infield rectum constraints, 9 of whom had a single deviation\2%. Maximum toxicity was grade 0, 1, and 2 in 69%, 23%, and 8%, respectively. Infield rectal mean/median doses, D75, V30, and V40 were associated with grade 2 toxicity (p’s\0.05); there was no toxicity association with rectum, ARWand infield ARW parameters. Post-tx BAS were marginally associated (p = 0.065), but only hemorrhoid history was significantly associated (p = 0.025) with grade 2 toxicity.

Conclusions: Prostate image-guided-IMRT using a daily ERBH2O shows low rates of acute GI toxicity compared to published studies when using strict infield rectum DVH constraints. Intermediate dose-level infield rectal parameters were associated with acute toxicity, but not anatomically-contoured rectum, suggesting clinical importance of more stringent rectal constraint application in the highest-dose region.

Acute and Late Toxicity Report of Post-Prostatectomy Proton Therapy for Prostate Cancer Patients Undergoing Adjuvant or Salvage Radiotherapy
Akansha Jain, Neha Vapiwala MD, Kristina D Woodhouse MD, Stefan Both PhD, Peter Gabriel MD, Zelig Tochner MD, Curtiland Deville MD, University of Pennsylvania, Memorial Sloan Ketering Cancer Center, Johns Hopkins University

Purpose: The role of radiotherapy after prostatectomy for prostate cancer is becoming increasingly defined. Adjuvant randomized trials have demonstrated improvements in biochemical relapse-free survival and overall survival for certain patients, generally at the expense of mild to moderate increased toxicity. The additive acute and late treatment morbidities of radiotherapy in these settings are generally a concern in this pa:ent population presenting with increased underlying urinary dysfunction post prostatectomy. Proton therapy (PT) is a long-established treatment modality for the treatment of intact prostate cancer given its favorable physical proper:es including the beam’s finite range and virtual lack of exit dose translating to reductions in integral, low, and intermediate dose regions compared to Intensity Modulated Radiation Therapy (IMRT), offering the poten:al of decreasing normal tissue toxicity. The purpose of our study was to report the acute and late genitourinary (GU) and gastrointestinal (GI) toxicities associated with post-prostatectomy proton therapy.

Materials/Methods: All patients (N=100) undergoing post-prostatectomy PT on an IRB-approved protocol from 2010-2015 were assessed. Existing medical databases and electronic medical records were used to identify all patients. Patients received a median dose of 70.2 Gy relative biological effectiveness (RBE) in 39 fractions with a 100 cc water-filled endorectal balloon (RadiaDyne, Houston, TX). Patients prescribed combined PT and IMRT to achieve pre-defined institutional dose constraints at initial intent were included. The decision to treat with PT was based on a combination of clinical factors, including oncologic and anatomic suitability for each modality, patient preference, and insurance coverage, as assessed initially by the treating physician and then by a multidisciplinary triage commieee, which rendered a final decision regarding suitability. Demographic & clinical characteristics, patient reported IPSS, IIEF, bowel function and bother scores, and maximum GU and GI toxicities during treatment and follow-up were collected. Toxicity was scored by CTCAE v4.0.

Conclusions: Acute and late maximum GU and GI toxicities were predominantly of grade 0 and 1. Grade 2 GU and GI toxicities were present but were of lesser frequency and there were no grade 3 toxicities. We report the clinical feasibility and favorable acute and late GU and GI toxicity profile of postprostatectomy proton therapy.

A Case-Matched Study of Toxicity Outcomes After Proton Therapy and Intensity Modulated Radiation Therapy for Prostate Cancer
Penny Fang, MD, Rosemarie Mick, MS, Curtiland Deville, MD,Stefan Both, PhD, Justin E. Bekelman, MD, John P. Christodouleas, MD, MPH, Thomas J. Guzzo, MD, MPH, Zelig Tochner, MD, Stephen M. Hahn, MD, and Neha Vapiwala, MD, Department of Radiation Oncology, University of Pennsylvania, Cancer; 121:1118-27, 2015

Purpose: The authors assessed whether proton beam therapy (PBT) for prostate cancer (PCa) was associated with differing toxicity compared with intensity-modulated radiation therapy (IMRT) using case-matched analysis.

Materials/Methods: From 2010 to 2012, 394 patients who had localized PCa received 79.2 Gray (Gy) relative biologic effectiveness (RBE) delivered with either PBT (181 patients) or IMRT (213 patients). Patients were case-matched on risk group, age, and prior gastrointestinal (GI) and genitourinary (GU) disorders, resulting in 94 matched pairs. Both exact matching (risk group) and nearest-neighbor matching (age, prior GI/GU disorders) were used. Residual confounding was adjusted for by using multivariable regression. Maximum acute and late GI/GU Common Terminology Criteria for Adverse Events-graded toxicities were compared using univariate and multivariable logistic and Cox regression models, respectively.

Results: Bladder and rectum dosimetry variables were significantly lower for PBT versus IMRT (P.01). The median follow-up was 47 months (range, 5-65 months) for patients who received IMRT and 29 months (range, 5-50 months) for those who received PBT. On multivariable analysis, which exploited case matching and included direct adjustment for confounders and independent predictors, there were no statistically significant differences between IMRT and PBT in the risk of grade 2 acute GI toxicity (odds ratio, 0.27; 95% confidence interval [CI], 0.06-1.24; P5.09), grade 2 acute GU toxicity (odds ratio, 0.69; 95% CI, 0.32-1.51; P5.36), grade 2 late GU toxicity (hazard ratio, 0.56; 95% CI, 0.22-1.41; P5.22), and grade 2 late GI toxicity (hazard ratio, 1.24; 95% CI, 0.53-2.94; P5.62).

Conclusions: In this matched comparison of prospectively collected toxicity data on patients with Pca who received treatment with contemporary IMRT and PBT techniques and similar dose-fractionation schedules, the risks of acute and late GI/GU toxicities did not differ significantly after adjustment for confounders and predictive factors.

Fiducial Markers, Saline, and Balloons to Locate and Stabilize the Prostate during Proton Therapy
Ross Zeitlin, BA., Mathew McPhillios, BS., Stephanie Harris, MD., Stephen Mandia, MD., Christopher R. Williams, MD., Joseph Costa, DO., Christopher G. Morris, MS., Zhong Su, PhD., Zuofeng Li, DSc., Nancy P. Mendenhall, MD., Int. J. Particle Ther. 2015; Issue 2(1); 29–36.

Purpose: To determine the value of fiducials in daily image-guided prostate targeting for proton therapy (PT), to compare intrafraction motion between two stabilization strategies (rectal saline and balloon), and to determine the respective impacts of these combined strategies on planning target volume (PTV) expansions and smearing margins.

Materials/Methods: Forty patients were randomly selected from a pool of low-risk prostate cancer patients with intraprostatic fiducials treated with proton therapy between 2006 and 2012, including 20 with intrarectal saline or 20 with endorectal balloons for daily prostate stabilization. Daily pre- and post-treatment orthovoltage (kV) films and digitally reconstructed radiographs (DRRs) were analyzed to determine prostate interfraction displacement, intrafraction motion, daily residual setup error in three axial dimensions (anterior-posterior, superior-inferior, and left-right), necessary population PTV expansions using van Herk’s formula (2.5R . 0.7r), and smearing margins.

Results: Interfraction displacement population means did not differ significantly in either treatment group. Intrafraction displacement population means in the anteriorposterior direction were significantly smaller with balloons than with saline. With fiducial markers to account for interfraction motion, PTV margins could be reduced by 4.0, 4.2, and 2.3 mm in the anterior-posterior, superior-inferior, and left-right directions, respectively, in saline-treated patients, and by 6.3, 6.8, and 0.8 mm in each direction, respectively, in balloon-treated patients. With fiducials, PTV margins were smaller using rectal balloons compared with saline: 2.3 vs. 3.6 mm in the anterior-posterior direction, 2.7 vs. 3.4 mm in the superior-inferior direction, and 1.1 vs. 2.0 mm in the leftright direction. The maximum smearing margin in balloon patients were 10.7 mm.

Conclusions: Fiducial markers are valuable for reducing the PTV expansion necessary to account for interfraction displacement. Rectal balloons were more effective than saline in decreasing intrafraction prostate motion, thereby permitting smaller PTV expansions to reduce the amount of normal tissue included in the target volume.

Effectiveness of a Novel Gas-Release Endorectal Balloon in the Removal of Rectal Gas for Prostate Proton Radiation Therapy
Landon S. Wootton, Rajat J. Kudchadker, A. Sam Beddar, Andrew K. Lee, Department of Radiation Physics, The University of Texas MD Anderson Cancer Center, Houston, TX, J Appl Clin Med Phys. 6;13(5):3945, Sept. 2012

Abstracts: Endorectal balloons (ERBs) are routinely used in prostate proton radiation therapy to immobilize the prostate and spare the rectal wall. Rectal gas can distend the rectum and displace the prostate even in the presence of ERBs. The purpose of this work was to quantify the effects an ERB with a passive gas release conduit had on the incidence of rectal gas. Fifteen patients who were treated with a standard ERB and 15 with a gas-release ERB were selected for this retrospective study. Location and cross-sectional area of gas pockets and the fraction of time they occurred on 1133 lateral kilovoltage (kV) images were analyzed. Gas locations were classified as trapped between the ERB and anterior rectal wall, between the ERB and posterior rectal wall, or superior to the ERB. For patients using the standard ERB, gas was found in at least one region in 45.8% of fractions. Gas was trapped in the anterior region in 37.1% of fractions, in the posterior region in 5.0% of fractions, and in the sigmoid region in 9.6% of fractions. For patients using the ERB with the gas-release conduit, gas was found in at least one region in 19.7% of fractions. Gas was trapped in the anterior region in 5.6% of fractions, in the posterior region in 8.3% of fractions, and in the sigmoid region in 7.4% of fractions. Both the number of fractions with gas in the anterior region and the number of fractions with gas in at least one region were significantly higher in the former group than in the latter. The cross-sectional area of trapped gas did not differ between the two groups. Thus gas-release balloon can effectively release gas, and may be able to improve clinical workflow by reducing the need for catheterization.

Conclusions: Lateral kV images from daily radiation treatments of 30 prostate cancer patients treated at our institution were examined for the presence of rectal gas. A standard ERB was used for 15 patients, and a modified ERB designed to passively allow gas release was used for the remaining 15 patients. The modified ERB significantly decreased the overall frequency of fractions with gas present in any region by decreasing the frequency of fractions with gas present between the rectal balloon and the anterior rectal wall, the most common location of rectal gas. We conclude, therefore, that the gas-release ERB effectively removes rectal gas and should be used in patients receiving proton radiation therapy.

Dosimetric Impacts of Endorectal Balloon in CyberKnife Stereotactic Body Radiation Therapy (SBRT) for Early-Stage Prostate Cancer
Hong F. Xiang, Hsiao-Ming Lu, Jason A. Efstathiou, Anthony L. Zietman, Ricardo De Armas, Kathryn Harris, B. Nicolas Bloch, Muhammad Mustafa Qureshi, Sean Keohan, Ariel E. Hirsch, Internatiopnal Journal Appl. Clin. Med. Phys. 2017 May; 18 Vol 3:37-43.

Purpose: In SBRT for prostate cancer, higher fractional dose to the rectum is a major toxicity concern due to using smaller PTV margin and hypofractionation. We investigate the dosimetric impact on rectum using endorectal balloon (ERB) in prostate SBRT.

Materials/Methods: Twenty prostate cancer patients were included in a retrospective study, ten with ERB and 10 without ERB. Optimized SBRT plans were generated on CyberKnife MultiPlan for 5 9 7.25 Gy to PTV under RTOG-0938 protocol for early-stage prostate cancer. For the rectum and the anterior half rectum, mean dose and percentage of volumes receiving 50%, 80%, 90%, and 100% prescription dose were compared.

Results: Using ERB, mean dose to the rectum was 62 cGy (P = 0.001) lower per fraction, and 50 cGy (P = 0.024) lower per fraction for the anterior half rectum. The average V50%, V80%, V90%, and V100% were lower by 9.9% (P = 0.001), 5.3% (P = 0.0002), 3.4% (P = 0.0002), and 1.2% (P = 0.005) for the rectum, and lower by 10.4% (P = 0.009), 8.3% (P = 0.0004), 5.4% (P = 0.0003), and 2.1% (P = 0.003) for the anterior half rectum.

Conclusions: Significant reductions of dose to the rectum using ERB were observed. This may lead to improvement of the rectal toxicity profiles in prostate SBRT.

Endorectal Balloon in Stereotactic Body Radiation Therapy (SBRT) for Early-Stage Prostate Cancer: A Planning and Dosimetry Analysis
H.F. Xiang, H. Lu, A.E. Hirsch, J.A. Efstathiou, A.L. Zietma, K. Harris, N. Bloch, S. Keohan, J. Willins, L.A. Kachnic, Int. J. Radiat Oncol Biol Phys; Vol 84 , Issue 3; S832, 2012

Purpose: The use of an endorectal balloon (ERB) has been reported to significantly reduce intra-fractional prostate motion during standard fractionated intensity-modulated radiation therapy (IMRT) for prostate cancer. Recently, hypofractionated IMRT and SBRT strategies are under investigation; however, to date, there have been no dosimetric analyses on the use of ERB with these approaches. This study investigates the dose-volume characteristics for the rectum when using ERB as part of SBRT planning for early-stage prostate cancer.

Materials/Methods: Twelve patients with prostate cancer who had received conventional IMRT at our institutions were included in this study. Six patients (Group-ERB) had been planned and treated with ERB containing 60-100 cc of water, and the other six (Group-noERB) without ERB. For each case, an optimized SBRT plan was generated by using sequential optimization in TPS according to the 5 fraction (5 x 7.25 Gy) dose-specification and dose-volume constraints of the RTOG 0938 randomized phase II study of hypofractionated RT for early-stage prostate cancer. Dosimetric characteristics for the rectum were compared between the two groups, including maximum dose, mean dose for the entire rectum and the anterior half of the rectum, and the percentages of rectal volume and anterior-half rectal volume receiving 50%, 80%, 90% and 100% of the prescription dose (36.25 Gy).

Results: While the maximum dose to the rectum was comparable between the two groups (range 37.8-39.9 Gy), the mean dose to the entire rectum was lower for Group-ERB (10.3 Gy, range 8.2-13.5 Gy) than Group-noERB (12.9 Gy, range 11.4-15.1 Gy). The mean dose to the anterior half of the rectum was also lower for Group-ERB (15.0 Gy, range 13.0-19.5 Gy) than Group-noERB (16.2 Gy, range 12.2-19.1 Gy). A consistent dosimetric advantage was also noted in the rectal volume receiving 50%, 80%, 90% and 100% of the prescription dose for Group-ERB compared to Group-noERB. The mean V50%, V80%, V90% and V100% of the entire rectum for Group-ERB was 16.7%, 6.3%, 3.5% and 0.9%, in comparison to 26.3%, 10.9%, 6.3% and 1.4% for Group-noERB. Similarly, the mean V50%, V80%, V90% and V100% of the anterior half of the rectum for Group-ERB was 31.6%, 11.8%, 6.6% and 1.6%, in comparison to 39.7%, 18.4%, 10.6% and 2.6% for Group-noERB.

Conclusions: Consistent rectal dose-volume improvements were observed with the use of endorectal balloons in five fraction SBRT treatment planning for early-stage prostate cancer. Confirmation of these dosimetric results with additional cases is warranted before investigating the impact of ERB on minimizing acute and long-term rectal toxicity.

Reduction of Treatment Times in CyberKnife Prostate SBRT Using a Water Filled Rectal Balloon
Desai P, Caroprese B, McKellar H, American Association of Physicists in Medicine,Volume 41, Issue 6 June 2014

Purpose: To illustrate 25% reduction in CyberKnife prostate SBRT treatment times using a water filled rectal balloon.

Materials/Methods: We perform prostate SBRT using a 3800cGy in 4 fraction regimen prescribed between 51% 59% iso-dose lines to 95% of PTV using a CyberKnife System. The resultant heterogeneous dosimetry is analogous to HDR dosimetry. Our patients are treated in a feet first supine position to decrease treatment couch sag and also to position the prostate anatomy closer to the robot. CT imaging is performed with a Radiadyne Immobiloc rectal balloon filled with 45-50cc water placed firmly inside the patient's rectum. A treatment plan is developed from this CT study using Multiplan. The patient is treated every other day for 4 days using the rectal balloon for each fraction. Gold fiducials previously implanted inside the prostate are used for tracking by the CyberKnife system.

Results: Critical structures comprise the usual GU anatomy of bladder, rectum, urethra, femoral-heads along with emphasis on doses to anterior rectal wall and rectal mucosa. The water filled rectal balloon localizes the rectum, which enables the physician to accurately contour both anterior rectal wall, and rectal mucosa. The balloon also has a gas release valve enabling better patient comfort. Rectum localization enables the CyberKnife system to make fewer corrections resulting in fewer treatment interruptions and time lost to re-adjustment for rectal motion, bowel filling and gas creation. Effective treatment times are reduced by 25% to approximately 45 minutes. Adoption of the balloon has required minimal change to our planning strategy and plan evaluation process.

Conclusions: Patient follow-up comparisons show no difference in effectiveness of treatment with and without balloons We conclude that rectal balloons enhance patient comfort and decrease effective treatment times.

Real-time In Vivo Dosimetry for SBRT Prostate Treatment Using Plastic Scintillating Dosimetry Embedded in a Rectal Balloon: A Case Study
Justin L. Cantley, Chee-Wai Cheng, Fredrick B. Jesseph, Tarun K. Podder, Valdir C. Colussi, Bryan J. Traughber, Lee E. Ponsky, and Rodney J. Ellis, Department of Radiation Oncology, University Hospitals, Cleveland, OH, USA; Department of Urology, University Hospitals, Cleveland, OH, USA, 2016

Purpose: The patient was a 55-year-old male with localized prostate cancer treated with linear-accelerator-based stereotactic body radiation therapy (SBRT) to deliver 36.25 Gy in 5 fractions of 7.25Gy per fraction. Due to the high-stakes nature of SBRT, it is prudent to employ some type of treatment delivery verification. In vivo dosimetry is commonly used in external beam radiation therapy in order to detect major errors in treatment delivery, to assess how well the delivered dose matches the planned dose, to record the actual dose received, and to fulfill legal requirements.(1,2) The dose to the rectal wall is of interest as the institution has plans to move forward with a new clinical trial that will treat partial prostate with linear-accelerator-based SBRT and dose to the rectal wall is a particular concern of the trial. As such, in vivo dosimetry measurements were made of the anterior rectal wall using plastic scintillators. Plastic scintillators are well suited for in vivo dosimetry measurements as they are water-equivalent; independent of angular incidence, dose rate, and energy; and have a linear relationship between dose deposited and light emitted,(3,4) However, newer generations of plastic scintillating materials exhibit a temperature dependence not found in previously used materials.

Materials/Methods: The patient was a 55-year-old male with localized prostate cancer clinical stage T1cN0M0, Gleason 7(3+4) initial PSA 6.6 ng/mL Stage IIa with ECOG performance status of 0. He presented for consultation inquiring about advanced radiotherapy techniques including proton therapy and stereotactic radiosurgery. His main concerns were late effects of the radiotherapy for quality of life. After consultation with an urologist and radiation oncologist to discuss management, he elected linear-accelerator-based stereotactic body radiation therapy (SBRT) to deliver 36.25 Gy in 5 fractions of 7.25 Gy per fraction. Fiducial markers were placed in the operating room transperineally by his urologist, and at the time of fiducial marker placement a hydrogel device (SpaceOAR, Augmenix Inc. Waltham, ME) was placed to separate the prostate and the rectal wall to reduce the risk for rectal toxicity related to the radiation exposure.(7) The OARtrac system (RadiaDyne, Houston, TX) is a new in vivo scintillation dosimetry system designed to measure rectal wall dose during prostate radiotherapy procedures. The OARtrac system uses a single-use prostate immobilization endorectal balloon (ERB) embedded with two independent plastic scintillation radiation detectors that provide near real-time dose verification for external beam irradiation of prostatic cancer.(7) Two plastic scintillating detectors (PSDs) are installed on the anterior surface and along the length of an endorectal balloon (labeled as proximal and distal, respectively).(8,9,10) These PSDs measure the dose at the prostatic rectal interface where the dose gradient is steep as the patient is being irradiated with megavoltage X-rays. The rectal balloon reduces the motion of the prostate gland to a minimum while at the same time maintains a constant shape of the rectum; see Fig. 1 for more details about the system. Use of the system is simplified by system-specific software. The system simply needs a few minutes to warm up, input the sensor used, and take a background measurement before each measurement. After each measurement, the user has the option to create a PDF report, and the measurement is saved in the system automatically. The sensors were precalibrated at the University of Texas MD Anderson Cancer Center Dosimetry Laboratory, but did require an on-site correction for SBRT treatments. During installation of the system, a dose verification test was performed to assess the accuracy of the pair of PSD detectors using a solid-water phantom and the patient-specific plan. These measurements were compared against the expected machine output under the same irradiation condition. To reduce the variability of detector response to radiation during the SBRT treatment, a total of five different PSDs pairs were placed sequentially in the solid-water phantom and measured under the same conditions. Using the measured values, a single system adjustment was made to ensure the dose measurement accuracy. The PSD sensors used during patient treatment were then tested using the solid-water phantom and the patient-specific plan, which allowed for a controlled test with minimal positional uncertainty. Differences between the measured dose and the planned dose were found to be within 2% and 1%, on average, for the proximal and distal sensors respectively when using the solid-water phantom. This was done to test the accuracy of the various sensors used for dose measurements during treatment. For patient treatments, the system was used to measure real-time dose delivered to the patient prostatic rectal interface for each fraction. The measured dose was compared to the computed dose to the rectal wall for SBRT from the treatment planning system (Pinnacle, Philips Healthcare, Madison, WI). The computed dose was found by creating a region of interest (ROI) and determining the mean dose to the ROI. PSD location was determined using the location of the fiducial in the sensor and the known distances between the fiducial and the sensors. In addition, fraction-specific computed dose was found to compare with the measured dose. This was done using the cone-beam CT (CBCT) taken between the two treatment arcs. This CBCT was chosen because it was thought to be the most representative of the total treatment fraction. The CBCT was exported to MIM (MIM Software, Cleveland, OH), a software that allowed the CBCT to be fused to the original treatment planning CT and the treatment planning dose transferred to the CBCT. Rigid registration was performed based upon fiducials in the prostate, as this was the method used during patient treatment since the distance between the anterior rectal wall and the prostate was minimal. Each of the system’s ERB sensors included a fiducial between the two PSDs which was visible in each CBCT, and allowed a better approximation of the placement of the PSD sensors, which might suffer from interfractional positional variation. This information was used to determine a more appropriate predicted dose for each individualfraction. For each treatment fraction, a new endorectal balloon (ERB) and sensor was used. Residual air was removed from the balloon to prevent gas pockets and it was then filled with water before insertion into the rectal cavity. The ERB was placed with lubricating gel with the PSD devices positioned to press on the anterior rectal wall to improve heterogeneity. The balloon was filled to a total of 40 cc of water to help immobilize the gland without exerting excess pressure against the prostate since the excess pressure could move the rectal wall closer to the PTV. Once the balloon was inserted and filled, it was retracted to hold against the anal sphincter. The external rectal stopper was locked onto the shaft of the balloon at the same distance from the tip each day for reproducibility to match the daily treatment distance from the anal verge. Radiation dose measured for each treatment fraction consisted of two treatment arcs and a CBCT taken between the two arcs. Any dose measured from the CBCT was subtracted from the final reading so that only the treatment dose was considered. The only change to the workflow of a typical prostate treatment using a rectal balloon was the presence of a physicist trained to use the OARtrac system. Setup of the system (machine warm-up, connection of sensors, and background measurements) was able to be performed during patient positioning so that treatment was not prolonged or delayed. At the time of the final consultation, informed consent was obtained to proceed with SBRT for the prostate gland using fiducial markers and hydrogel placement prior to treatment planning, as well as for daily use of the PSD and ERB device during treatment to record the in vivo rectal dose. While the hydrogel was placed to provide distance between the rectal wall and the prostate, the use of the PSD and ERB system was not only to measure rectal wall dose in vivo, but also to prevent prostate motion during the SBRT delivery to maximize the benefit from image guidance during the procedure in a complimentary fashion for each device to improve patient safety and treatment delivery. Utilizing both technologies allowed us to limit average rectal wall dose to 36.9% of prescribed daily dose to the prostate gland and verify this in vivo. All procedures were performed in accordance with the ethical standards set forth by the IRB committee and with the Helsinki Declaration of 1975, as revised in 2000.

Results: The measured doses were compared to the expected doses from the treatment planning software and the fraction-specific doses from the MIM software. The expected doses were found in two ways: first, expected doses were found in the treatment planning system using only the treatment planning CT and, second, expected doses were found in MIM using the CBCT of each individual fraction. If daily CBCT images were not available, expected doses would only be available from the treatment planning system using the treatment planning CT. The results are summarized in Tables 1 and 2. While the average measured dose at the proximal detector was 431.9 cGy as compared to 458.0 cGy calculated dose (about 6% below predicted value) and the average measured dose at the distal detector was 512.9 cGy as compared to the calculated dose of 456.7 cGy (12.3% higher dose value than expected value), the overall average of measured dose difference was 6% of predicted dose. Thus it correlates well with the average detected doses in the solid-water phantom. The measured daily doses showed a wide range of agreement with the expected doses, and the main reason was believed to be positioning uncertainty. Other causes for discrepancy certainly could affect the readings as well. While the positional change in the endorectal balloon was the most likely cause, patient positioning and alterations in the delivered dose due to inhomogeneous tissue density within the adjacent region of the detector such as bowel gas might also have contributed. Additionally the very steep drop-off of dose with SBRT compared with standard radiotherapy accentuates the difference. A HexaPOD couch (Elekta, Stockholm, Sweden) was used for fiducial alignment to correct for tilt of the pelvis to help minimize uncertainty and to align the prostate to the planning position prior to the start of treatment. A total of three CBCT scans were taken with one prior to the treatment, one between the two treatment arcs, and one after the treatment to account for positional uncertainty during treatment as best as able. For SBRT treatments, the dose gradient is high at the periphery of the target volume and a difference of a few millimeters can result in large changes in dose (see Figs. 2 and 3). Using the MIM software, it was possible to find the distance to agreement (DTA), which was the shortest distance from the estimated location of the PSD to the location that had the exact same calculated dose as the dose measured by the PSD.

Conclusions: While this manuscript is exploratory in reporting the first ever use of this novel device in a patient for treatment delivery using SBRT to treat prostate cancer, the clinical implications are very pertinent to improving patient care. By providing an in vivo reading of actual delivered daily dose, it may help to reduce treatment errors in daily setup or initial dose calculations. Patient safety and treatment efficacy are improved through the use of the technology, especially in the setting of hypofractionated treatments, where a daily error can result in a larger deviation in total delivered dose. We are now utilizing this technology in a novel partial prostate SBRT protocol and should anticipate the ability to provide further updates in patient reported outcomes. This is the first reported case using both a hydrogel and the in vivo dosimetry system with PSDs and ERB to maximally reduce dose to the rectal wall and minimize prostate motion during SBRT to reduce late rectal toxicity. This will now be further clinically evaluated on an IRB-approved prospective study in 12 patients using OARtrac system without a hydrogel device. The goal of this study will be to treat a limited volume of the prostate gland as defined through a combination of both anatomic and functional MRI sequencing and correlated with tracked histopathological evaluation in and around the index lesion to define a planning target volume for a 3-fraction regimen of SBRT of 9.75 Gy per fraction to a total dose of 29.25 Gy. This trial will be using a quality of life endpoint to evaluate treatment tolerance and side effects in addition to biochemical response with PSA and serial MRI imaging. The use of OARtrac system in this study was initiated as a result of a recommendation by the protocol review and monitoring committee to track daily delivered dose to assure patient safety and will be correlated to patient reported toxicities. The results from this trial will be the subject of a future manuscript.

Intended Use and Product Information:

The RadiaDyne® ImmobiLoc® Prostate Immobilization Treatment Balloon Device is designed as an immobilizer to assist in positioning the prostate in a more predictable and reproducible location during the computed tomography (CT) exam and radiation treatment (RT) therapy. The product is packaged in a kit configuration which includes the following components to perform the procedure: Non-latex Rectal Balloon Device, depth stopper, surgical lubricant, syringe, and instructions for use manual.

Indication For Use:

The RadiaDyne® ImmobiLoc® Prostate Immobilization Treatment Rectal Balloon is a single use, disposable, flexible, inflatable, non-powered positioning device, intended to be used on a daily treatment basis for the temporary positioning of the rectal wall and adjacent structural anatomies of male patients who require radiation therapy for Prostate Cancer Treatment. The purpose of the device is to stabilize the prostate during computed tomography (CT) exam, X-ray, or radiation treatments (RT). The placement of the balloon requires a physician or a physician directed health care professional, and it is performed as a separate procedure outside of the standard (CT) exam and (RT) treatment.


Peri-rectal / Peri-anal abscess
Anal Fissure
Prior low anterior resection
Rectal Fistula
Rectal Fissure
Rectal Ulcer
Anal Canal Stricture
Surgery of the prostate, rectum or surrounding area within the last eight weeks
Radiation of the rectum or surrounding area within the last eight weeks
Any standard exclusionary criteria recognized for endo-rectal / intra-rectal devices

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