Florida, Jacksonville, FL. Purpose/Objective(s): To assess the usefulness of dose-volume constraints for minimizing the risk of rectal toxicity with image-guided.
Poster Viewing Abstracts S385
Volume 84 Number 3S Supplement 2012 Author Disclosure: R.G. Stock: None. J.T. Liu: None. S.R. Blacksburg: None. N.N. Stone: G. Consultant; Nihon Medi Physics, Ferring.
2441 The Value of Dose Constraints in Minimizing Rectal Toxicity in Patients Receiving Radiation Therapy for Prostate Cancer: Threeyear Analysis of Toxicity Outcomes in 2 Prospective Trials of Image Guided Proton Therapy for Early- and Intermediate-Risk Prostate Cancer N.P. Mendenhall,1 Z. Li,1 B.S. Hoppe,1 R.B. Marcus,1 W.M. Mendenhall,1 R.C. Nichols,1 C.G. Morris,1 C.R. Williams,2 J. Costa,2 and R. Henderson1; 1University of Florida Proton Therapy Institute, Jacksonville, FL, 2Division of Urology, College of Medicine, University of Florida, Jacksonville, FL Purpose/Objective(s): To assess the usefulness of dose-volume constraints for minimizing the risk of rectal toxicity with image-guided proton therapy for early- and intermediate-risk prostate cancer. Materials/Methods: One hundred seventy-one prostate cancer patients accrued to prospective institutional review board-approved trials of 78 cobalt gray equivalent (CGE) in 39 fractions for low-risk disease or dose escalation from 78 to 82 CGE for intermediate-risk disease. Minimum potential follow-up was 3 years. Toxicity rates were correlated with clinical factors and prospectively calculated dose volume relationships to organs at risk. Results: One of 89 low-risk and 1 of 82 intermediate-risk patients had disease progression. Three-year biochemical progression-free survival (bPFS) and overall survival rates for the combined group are 99% and 95%, respectively. Only 2 patients developed grade 3+ gastrointestinal toxicities: both were on anti-coagulation and both events resolved after intervention and did not recur. The prevalence and cumulative incidence of all grade 2+ gastrointestinal toxicity at 3 years were 7.1% and 14.1%, respectively. The majority of events were rectal bleeding with or without proctitis. Multivariate analyses showed significant correlation between grade 2+ rectal bleeding and/or proctitis and the percent of rectum receiving doses ranging from 30 CGE to 75 CGE (V30, p Z 0.0475; V70, p Z 0.0199; and V75, p Z 0.0152). Conclusions: Outcomes at 3 years with image-guided proton therapy in doses up to 82 CGE, based on organ-constraints and the techniques used in this study, continue to suggest high efficacy and minimal toxicity. There appears to be a very steep dose response for manifestation of rectal injury and the volume of rectum receiving doses between 70 and 75 CGE. The correlation noted between grade 2+ rectal bleeding and /or proctitis and various dose-volume parameters may be useful in designing dose-volume constraint goals for organs at risk in future clinical trials. Author Disclosure: N.P. Mendenhall: None. Z. Li: None. B.S. Hoppe: None. R.B. Marcus: None. W.M. Mendenhall: None. R.C. Nichols: None. C.G. Morris: None. C.R. Williams: None. J. Costa: None. R. Henderson: None.
2442 Rectum and Bladder Dose Variations During the Course of Image Guided Radiation Therapy for Postoperative Prostate Cancer M. Akin,1 F.O. Dincbas,1 D.C. Oksuz,1 B. Iktueren,1 P. Ambarcioglu,2 S.K. Cavdar,1 and S. Koca1; 1Istanbul University Cerrahpasa Medical School Department of Radiation Oncology, Istanbul, Turkey, 2Istanbul University Cerrahpasa Medical School Department of Biostatistics, Istanbul, Turkey Purpose/Objective(s): To assess the changes in rectum and bladder doses during the course of IMRT or IMAT of postoperative prostate cancer with kv-Cone beam CT (kV CBCT) image-guidance. Material/Methods: The data from 20 prostate cancer patients who were referred to our department between the dates of January 2010 - December 2011 for postoperative radiation therapy were retrospectively assessed. Both the planning tomography and kV-CBCT were performed following local protocols for bladder and rectum preparations. The target and critical
organs were delineated 2.5 mm sliced planning CT according to RTOG atlas. PTV was formed by giving safety margins 0.5 cm posteriorly and 0.8 cm at other directions to CTV. All of the treatments were planned using a treatment planning system to receive 66 Gy in 33 fractions using IMRT or IMAT plans. Target localization was performed on the basis of soft tissue matching using CBCT scans before each treatment. Sixteen CBCT, which were taken at the first 5 days of treatment and then 2 times per week for each patient, were used for assessments. Bladder and rectum were recontoured on each CBCT images offline by a single physician and the delivered doses were recalculated. The resulting rectum and bladder dose distributions, as delivered were compared to those of the original treatment plans. The DVH parameters of the bladder and rectum studied were the volumes receiving 40 Gy, 50 Gy, 60 Gy and 2 cc, mean, minimum doses. The volumes of rectum and bladder receiving greater than 40 Gy, 50 Gy and 65 Gy are compared to the initial plan prediction using paired T test. In order to analyze the variations for the bladder and rectum for each patient, ANOVA test was performed. Results: Based on 320 kV-CBCT sets, most of the dose volume variations for rectum and bladder were significantly (p < 0.05) higher than predicted, except for the doses received by 2 cc of bladder and V50,V60 of rectum. The dose distributions for bladder did not meet our criteria for V6525% and V4050% in 10% and 20% of the patients, respectively. None of the rectal DVH showed V6517%, but in 11 patients rectal doses did not meet with our acceptance criteria of V4035%. There was no significant difference between the variations for each patient with ANOVA test. Conclusion: Although all of the patients were treated with empty rectum and full bladder in this study, the doses observed were higher than predicted. It seems that rectal and bladder volume varies inter fractionally, however the majority of bladder and rectum doses meet our criteria. While the initial treatment plan cannot be assumed to represent accurate doses, the patients should be treated with daily CBCT image guidance to assess daily bladder and rectum volume changes. Author Disclosure: M. akin: None. F.O. Dincbas: None. D.C. Oksuz: None. B. Iktueren: None. P. Ambarcioglu: None. S.K. Cavdar: None. S. Koca: None.
2443 Impact of Proton Therapy to the Prostate Alone Versus the Whole Pelvis on Patient-reported Outcomes and Toxicities in High-Risk Prostate Cancer Patients L.A. McGee,1 B.S. Hoppe,2 R.H. Henderson,3 C.G. Morris,4 R.C. Nichols,3 Z. Su,3 Z. Li,3 W.M. Mendenhall,4 C.R. Williams,5 and N.P. Mendenhall3; 1University of Florida College of Medicine Shands Hospital, Gainesville, FL, 2University of Florida Proton Therapy Institute, Jacksonville, FL, 3University of Florida Proton Therapy Institute, Jacksonville, FL, 4University of Florida, Gainesville, FL, 5University of Florida Proton Therapy Institute, Gainesville, FL Purpose/Objective(s): To investigate quality of life (QOL) outcomes and gastrointestinal (GI) toxicity in men with high-risk prostate cancer undergoing definitive prostate-only proton therapy (POPT) versus wholepelvis radiation therapy (WPRT). Methods and Materials: From 2006 to 2011, 192 men with high-risk prostate cancer were treated with definitive POPT (n Z 149) or WPRT (n Z 43). WPRT was delivered using photon-based intensity-modulated radiation therapy (IMRT) per the Radiation Therapy Oncology Group atlas followed by a proton boost to the prostate. Indications for WPRT included either a 15% risk of lymph node involvement per Memorial SloanKettering Cancer Center prostate cancer nomogram (n Z 40) or nodepositive disease (n Z 3). Men receiving WPRT were more likely to be younger than age 60 (23% vs. 11%) and to have received androgen deprivation therapy (70% vs. 56%). Toxicity was assessed per CTCAE v3.0 weekly during treatment and every 6 months thereafter. Expanded Prostate Cancer Index Composite (EPIC) questionnaires were collected at baseline and every 6 months. Prostate-specific antigen was evaluated every 3 months.
