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Outcomes and Toxicity for Treatment of Adrenal Metastases With Radiation Therapy
Volume 96 Number 2S Supplement 2016 Purpose/Objective(s): The aim of this study was to evaluate the PSA response rate, biochemical relapse-free survival, and toxicity in bone oligometastatic prostate cancer patients who had undergone definitive intensity modulated radiation therapy (IMRT) for both primary tumor and all metastatic lesions. Materials/Methods: From 10/2011 to 9/2015, 22 prostate cancer patients with bone oligometastases (no more than 5 metastatic lesions) were treated. Metastatic lesions were documented by positive bone scan or CT scan or MRI. All patients received IMRT, 40-76Gy in 10-38 fractions (median dose: 60Gy) to metastatic lesions, 45-46Gy to the whole pelvis (for 14 patients, 63.6%) and 72-76Gy to the prostate and seminal vesicles. All patients received MAB using a LHRH agonist or orchiectomy together with an oral anti-androgen before and during RT. After RT, all patients received continuous ADT except one due to cardiovascular disease. Survival was calculated using the Kaplan-Meier method. Results: A total of 49 bone metastatic lesions were identified in these 22 patients. The median number of metastatic lesions per patient was 2 (range 1-5). Twenty-nine (59.1%) lesions were localized in the pelvis, 14 (28.6%) in the spines, 3 (6.1%) in the femurs and 3 (6.1%) in the ribs. The median follow-up was 17 months (range: 2-48 months). The median duration of ADT before RT was 5 months and the median pre-RT PSA was 0.7ng/ml. PSA response rate: 20 patients had a PSA decline 2 months after RT, and 13 of them decreased to <0.1ng/ml (59.1%). The rate of biochemical relapse-free survival (bRFS) rates at 1-year and 2-year based on the nadir plus 2 ng/mL definition were 85.7% and 71.4%, respectively. Three patients had biochemical failure at 2, 13, and 24 months after RT, respectively. They all received the second line ADT and one of them developed lung metastases after 23 months of ADT. Additionally, no acute or late grade 3/4 GI or GU toxicity was recorded. Conclusion: Our study suggests that definitive IMRT is well tolerated and results in good PSA response and biochemical control in patient with bone oligometastatic prostate cancer. However, the long-term survival outcomes need to be further explored. Author Disclosure: X. Qi: None. X. Gao: None. H. Li: None. S. Qin: None. M. Zhang: None. X. Li: None. X. Li: None. M. Ma: None.
2665 Meeting Dose Objectives in Stereotactic Body Radiation Therapy for Prostate Cancer: Water- Versus Air-Filled Endorectal Balloon? L. Tsvang,1 A. Dubouloz,2 D. Alezra,3 Z. Symon,3 and R. Miralbell2; 1 Chaim Sheba Medical Center, Ramat Gan, Israel, 2Radiation Oncology, Hopitaux Universitaires de Geneve (HUG), Geneva, Switzerland, 3 Radiation Oncology, Sheba Medical Center, Tel Hashomer, Israel Purpose/Objective(s): To compare the achievement and cost of dose objectives defined for a European multicenter phase II trial of urethrasparing SBRT using water vs. air-filled endorectal balloon (ERB). Materials/Methods: Ten patients simulated with a 100cc filled ERB for prostate SBRT were analyzed. Hounsfield units in the balloon were adjusted for comparison of air and water. Prescription dose to the PTV was 36.25 Gy in 5 fractions of 7.25 Gy. The urethral dose prescription (urethral planning risk volume, uPRV) was 32.5 Gy. Treatment plans were optimized using volumetric intensity-modulated arc treatment (VMAT) technique and dose was delivered with two arcs. We hypothesized that the optimization algorithm would perform better with water-filled EBR vs. air due to homogeneity of tissue density. Thus, two optimizations were run for each air-filled balloon: one with the same objective template as water and a second improved optimization (IO) which drives improved PTV coverage. The plans were compared for following parameters according to the research protocol: PTV98%, PTV95%, PTV2%, PTV-Rectal wall intersection PTV-R 98%, PTV-R2%, PTV-Rmean, RwallDmax, Rwall100%, Rwall90%, Rwall80%, Homogeneity Index HI PTV-R. Results: The goal of PTV98% covered by the 95% prescription dose was achieved for all water-filled ERB and only 60% of air-filled ERB (P Z 0.02, chi2). Improved optimization (IO) for air achieved the goal in 80% of
Poster Viewing E273 air-filled ERB. The PTV-R98% (representing overlap of anterior rectal wall and PTV) dose coverage was significantly less for air vs. water: 89.1% 1.6 vs. 94.4%1.6 (P<0.0001), but increased to 94.3%1.8 with IO. The rectal volume Rwall100% was 0.25cc 0.16 vs. 1.87cc 0.69 for air vs. water (P<0.0002), however increases to 1.27cc 0.67 for IO. Conclusion: Water-filled ERB provide superior PTV coverage than air at the cost of exposing a greater volume of rectal tissue to doses above 100% of the prescription dose. Strategies to improve PTV coverage for air-filled ERB succeed in most patients, yet will increase dose to the anterior rectal wall. The clinical impact of exposing minute volumes of rectal wall to ultra-high doses is unknown and will be clinically correlated with longer follow-up of patients treated in this protocol. Author Disclosure: L. Tsvang: None. A. Dubouloz: None. D. Alezra: None. Z. Symon: None. R. Miralbell: None.
2666 Intermediate-Risk Prostate Cancer Treated With 3 Radioablative Regimens: Comparison of Robotic Ultrahypofractionation and High-Dose-Rate Brachytherapy Alone or Combined With External Beam Radiation Therapy P.A. Wojcieszek, M. Szlag, G. Glowacki, A. Cholewka, M. Fijalkowski, S. Kellas, B. Biala, and L. Miszczyk; MSC Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Gliwice, Poland Purpose/Objective(s): Evaluation of the morbidity and the outcomes among the intermediate-risk prostate cancer patients treated with three radiation therapy regimens using radioablative doses per fraction (>7Gy). Materials/Methods: One hundred eighty-three intermediate-risk prostate cancer patients were treated in the three prospective trials on the robotic ultrahypofractionation (RUH), the high-dose-rate brachytherapy alone (HDRalone) and the external-beam radiation therapy combined with the high-dose-rate boost (HDRboost). The regimens were 5x7.25Gy, 3x11Gy and 23-25x2Gy+1-2x10-10.5Gy for RUH, HDRalone and HDRboost, respectively. To minimize disparity the outcome blinded adjusting (i.e. 1:1:1 matching with following criteria: Gleason score, maximum PSA, T stage, age) was performed on the patients, who exceeded the follow-up of 6 months. Each group included 29 patients to total number of 87 patients enrolled into this study. Wilcoxon and Kruskal-Wallis tests were used to assess the differences among the groups. Kaplan-Meier analysis and logrank test were used to estimate the survival. Results: There were statistically significant differences between the groups. RUH had the highest maximal PSA (P-.0000), HDRboost had the highest T stage (P-.03), and both HDR groups had higher Gleason scores (P-.009). Median follow-up for RUH, HDRalone and HDRboost was 19, 16 and 36 months, respectively. HDRboost and RUH were significantly linked with mild gastrointestinal morbidity (P-.02). There were no differences between PSA levels between the groups at the last follow-up. Biochemical disease-free survival at 2 years was better for both HDR groups than RUH (100% vs 96%; P-0.09), however it was not significant. Conclusion: Regimens using radioablative doses per fraction are efficient, while yielding low morbidity. In spite of the necessity of the long-term results, comparison with conventional and/or hypofractionated externalbeam radiation therapy schedules should be performed with further randomized clinical trial design. Author Disclosure: P.A. Wojcieszek: None. M. Szlag: None. G. Glowacki: None. A. Cholewka: None. M. Fijalkowski: None. S. Kellas: None. B. Biala: None. L. Miszczyk: None.
2667 Outcomes and Toxicity for Treatment of Adrenal Metastases With Radiation Therapy W.G.A. Wang,1 K. Sura,1 J. Robertson,1 D.J. Krauss,1 P.Y. Chen,2 and I.S. Grills2; 1Beaumont Health, Royal Oak, MI, 2Beaumont Health System, Royal Oak, MI
E274
International Journal of Radiation Oncology Biology Physics
Purpose/Objective(s): To evaluate local control and toxicity in patients undergoing radiation therapy (RT) for adrenal metastases. Materials/Methods: This is a retrospective review of 26 patients who have undergone radiation therapy for adrenal metastases at our institution from 2008 to 2014. The median RT dose was 35Gy (30-50Gy) in 5 fractions (314). The most common fractionation scheme was 40Gy in 5 fractions. Patients were stratified based on their initial treatment intent. Palliative patients (Pt) (n Z 13) received radiation therapy due to pain and/or rapidly enlarging lesions. Oligometastatic patients (O) (n Z 13) underwent radiation therapy with the goal of slowing disease progression. Local control (LC), distant control (DC), overall survival (OS), and acute/late toxicities were evaluated. Results: The majority of the patients were male (62%) with median age of 66. 62% of patients had a non-small cell lung cancer primary (88% adenocarcinoma, 12% squamous cell carcinoma). 19 patients had left sided, 5 had right sided, and 3 had bilateral tumors. The median BED10 for the cohort was 53.6Gy (range 39-85.5Gy). The median BED10 for the O group was 72Gy (range 72-85.5Gy) and 48Gy (range 39-53.6Gy) for the Pt group. The dose range for the two groups did not overlap. The mean GTV was 58cm3. The average mean doses to the liver, kidney, and stomach for the O group were 4.2 Gy, 9.2 Gy, and 9.4 Gy respectively. The average duodenum maximum dose was 35Gy for the O group. Deliverable BED in O cases was dependent on adjacent normal tissue tolerance. Median OS for the entire cohort was 16 months. The 1/2 year OS for the cohort was 56%/26%. The 1/2 year OS was 79%/40% for the O group and 27%/9% for the Pt group (P Z 0.004). The 1 year DC was 14% for the O group and 8% for the Pt group. The 1/2 year LC for the cohort was 74%/43%. The 1/2 year LC was 81/54% for the O group and 67/0% for the Pt group (P Z 0.04). 9 out of 13 patients (70%) in the Pt group had improvement in their pain after RT. Treatments were well tolerated with 8 acute grade 1 nausea and only 1 acute grade 2 nausea/ vomiting. One patient who received bilateral adrenal treatment did develop grade 2 adrenal insufficiency as a late toxicity. Another patient may have developed an inflammatory/immune reaction with RT and nivolumab. He developed severe abdominal pain with diarrhea and died shortly after. Lack of documented GI toxicity limits dosimetric analyses for correlation. Conclusion: RT or SBRT was safely delivered to adrenal metastases and achieved palliative benefit in 70% of the patients. Local control may be limited by safely deliverable doses given adjacent stomach and small bowel, with an optimal BED to be determined. Prospective trials are required to evaluate the potential role for cure or prolonged progressionfree survival after SBRT for oligometastases. Author Disclosure: W.A. Wang: None. K. Sura: None. J. Robertson: None. D.J. Krauss: None. P.Y. Chen: Stock; Greater Michigan Gamma Knife. I.S. Grills: Stock; Greater Michigan Gamma knife. on the board of directors; Greater Michigan Gamma knife.
proton therapy at our institution. All 14 patients were planned with three-dimensional conformal proton therapy (3D-CPT) using two parallel opposed fields as well as comparison IMRT plans. A rectal balloon filled with water was used in all patients treated. Prescribed dose to the prostate was 79.2 Gy cobalt Gy equivalent (CBE). Dosevolume histograms were compared between the treatment plans. The Lyman-Kutcher-Burman model (n Z 0.09, m Z 0.13, and TD50 Z 76.9 Gy) was used to generate NTCP estimates for both IMRT and proton plans. Results: At least 95% of the planning target volume received the prescription dose for both proton and IMRT plans. Dose constraints placed on the rectum included volume receiving 65 Gy (V65) less than 17% and V40 less than 35%. The mean dose to the rectum was 24.8 Gy (range, 19.2-30.1 Gy) and 31.5 Gy (range, 23.7-39.4 Gy) for the proton and IMRT plans, respectively. The V65 constraint was unachievable in 3 of the proton plans and 3 of the IMRT plans. The mean V70 and V75 for proton plans were 8.7% and 5.7% compared to 7.4% and 4.9% for the IMRT plans. The mean NTCP for proton treatment plans was 7.7% (range, 2.7-11.7%) and 7.9% (range, 1.7-15.7%) for IMRT (P Z 0.46). After median follow-up of 9 months, no grade 2 or higher toxicity has been reported. Conclusion: Utilizing NTCP estimations, 3D-CPT proton therapy and IMRT have similar predicted rates of rectal toxicity. Currently, a Phase III randomized clinical trial is underway comparing proton therapy and IMRT with regards to rectal toxicity and quality of life. Author Disclosure: B.W. Fischer-Valuck: None. T.R. Mazur: None. H.A. Gay: None. L.A. Olsen: None. M.B. Altman: None. J.M. Michalski: None.
2668 A Treatment Planning Comparison of Proton Therapy and Intensity Modulated Radiation Therapy (IMRT) for Prostate Cancer Using the Normal Tissue Complication Probability (NTCP) B.W. Fischer-Valuck, T.R. Mazur, H.A. Gay, L.A. Olsen, M.B. Altman, and J.M. Michalski; Washington University School of Medicine, St. Louis, MO Purpose/Objective(s): The volume of rectum receiving high-dose radiation therapy (i.e. > or Z 60 Gy) is consistently associated with the risk of Grade > or Z 2 rectal toxicity, or rectal bleeding, based on common terminology criteria for adverse events (CTCAE). Our goal was to compare intensity-modulated photon radiation therapy (IMRT) with proton radiation therapy in regard to the rectal dose using the normal tissue complication probability (NTCP). Materials/Methods: All patients between July 2014 and January 2016 were enrolled on a prospective registry, and the first 14 consecutive low or intermediate risk prostate cancer patients were treated with
2669 Changes in Serum Testosterone 60 Months After Proton Therapy for Localized Prostate Cancer R.C. Nichols,1 C.G. Morris,1 C.M. Bryant,1 B.S. Hoppe,1 R.H. Henderson,1 W.M. Mendenhall,1 Z. Li,1 J.A. Costa,2 C.R. Williams,2 and N.P. Mendenhall1; 1University of Florida Health Proton Therapy Institute, Jacksonville, FL, 2Division of Urology University of Florida Health, Jacksonville, FL Purpose/Objective(s): Five studies (1-5) in the contemporary radiation therapy literature have demonstrated a +/-10% decline in Serum Testosterone (ST) for patients receiving x-ray therapy for prostate cancer e presumably due to scatter radiation to the testicular Leydig cells. Materials/Methods: Between August 2006 and October 2011, 399 patients with low and intermediate risk prostate cancer were enrolled on 3 prospective trials delivering between 70 Cobalt Gray Equivalent (CGE) and 82CGE at between 2CGE and 2.5CGE per fraction using passively scattered protons. Serum testosterone (ST) was to be checked at baseline and every 6 months after PT. ST was checked at baseline in 393 patients and at 60 months or later in 169 of these patients (who are the subject for this analysis). The analysis excluded 14 patients who received LHRH agonist therapy before PT and 2 patients who acknowledged taking exogenous testosterone medications after PT. Results: Median baseline ST for the analyzable patients was 374.4 ng/dl (range 120.1 to 791.0). Median ST 5 years after PT was 390.0 ng/dl (range 25.0 to 862.0). The difference was not statistically significant (P Z 0.9931). Conclusion: Passively scattered proton therapy was not associated with testosterone suppression 5 years after PT e suggesting that protons may be associated with less out of field scatter radiation compared with x-rays. Author Disclosure: R.C. Nichols: None. C.G. Morris: None. C.M. Bryant: None. B.S. Hoppe: None. R.H. Henderson: None. W.M. Mendenhall: None. Z. Li: None. J.A. Costa: None. C.R. Williams: None. N.P. Mendenhall: None.
2665 Meeting Dose Objectives in Stereotactic Body Radiation Therapy for Prostate Cancer: Water- Versus Air-Filled Endorectal Balloon? L. Tsvang,1 A. Dubouloz,2 D. Alezra,3 Z. Symon,3 and R. Miralbell2; 1 Chaim Sheba Medical Center, Ramat Gan, Israel, 2Radiation Oncology, Hopitaux Universitaires de Geneve (HUG), Geneva, Switzerland, 3 Radiation Oncology, Sheba Medical Center, Tel Hashomer, Israel Purpose/Objective(s): To compare the achievement and cost of dose objectives defined for a European multicenter phase II trial of urethrasparing SBRT using water vs. air-filled endorectal balloon (ERB). Materials/Methods: Ten patients simulated with a 100cc filled ERB for prostate SBRT were analyzed. Hounsfield units in the balloon were adjusted for comparison of air and water. Prescription dose to the PTV was 36.25 Gy in 5 fractions of 7.25 Gy. The urethral dose prescription (urethral planning risk volume, uPRV) was 32.5 Gy. Treatment plans were optimized using volumetric intensity-modulated arc treatment (VMAT) technique and dose was delivered with two arcs. We hypothesized that the optimization algorithm would perform better with water-filled EBR vs. air due to homogeneity of tissue density. Thus, two optimizations were run for each air-filled balloon: one with the same objective template as water and a second improved optimization (IO) which drives improved PTV coverage. The plans were compared for following parameters according to the research protocol: PTV98%, PTV95%, PTV2%, PTV-Rectal wall intersection PTV-R 98%, PTV-R2%, PTV-Rmean, RwallDmax, Rwall100%, Rwall90%, Rwall80%, Homogeneity Index HI PTV-R. Results: The goal of PTV98% covered by the 95% prescription dose was achieved for all water-filled ERB and only 60% of air-filled ERB (P Z 0.02, chi2). Improved optimization (IO) for air achieved the goal in 80% of
Poster Viewing E273 air-filled ERB. The PTV-R98% (representing overlap of anterior rectal wall and PTV) dose coverage was significantly less for air vs. water: 89.1% 1.6 vs. 94.4%1.6 (P<0.0001), but increased to 94.3%1.8 with IO. The rectal volume Rwall100% was 0.25cc 0.16 vs. 1.87cc 0.69 for air vs. water (P<0.0002), however increases to 1.27cc 0.67 for IO. Conclusion: Water-filled ERB provide superior PTV coverage than air at the cost of exposing a greater volume of rectal tissue to doses above 100% of the prescription dose. Strategies to improve PTV coverage for air-filled ERB succeed in most patients, yet will increase dose to the anterior rectal wall. The clinical impact of exposing minute volumes of rectal wall to ultra-high doses is unknown and will be clinically correlated with longer follow-up of patients treated in this protocol. Author Disclosure: L. Tsvang: None. A. Dubouloz: None. D. Alezra: None. Z. Symon: None. R. Miralbell: None.
2666 Intermediate-Risk Prostate Cancer Treated With 3 Radioablative Regimens: Comparison of Robotic Ultrahypofractionation and High-Dose-Rate Brachytherapy Alone or Combined With External Beam Radiation Therapy P.A. Wojcieszek, M. Szlag, G. Glowacki, A. Cholewka, M. Fijalkowski, S. Kellas, B. Biala, and L. Miszczyk; MSC Memorial Cancer Center and Institute of Oncology, Gliwice Branch, Gliwice, Poland Purpose/Objective(s): Evaluation of the morbidity and the outcomes among the intermediate-risk prostate cancer patients treated with three radiation therapy regimens using radioablative doses per fraction (>7Gy). Materials/Methods: One hundred eighty-three intermediate-risk prostate cancer patients were treated in the three prospective trials on the robotic ultrahypofractionation (RUH), the high-dose-rate brachytherapy alone (HDRalone) and the external-beam radiation therapy combined with the high-dose-rate boost (HDRboost). The regimens were 5x7.25Gy, 3x11Gy and 23-25x2Gy+1-2x10-10.5Gy for RUH, HDRalone and HDRboost, respectively. To minimize disparity the outcome blinded adjusting (i.e. 1:1:1 matching with following criteria: Gleason score, maximum PSA, T stage, age) was performed on the patients, who exceeded the follow-up of 6 months. Each group included 29 patients to total number of 87 patients enrolled into this study. Wilcoxon and Kruskal-Wallis tests were used to assess the differences among the groups. Kaplan-Meier analysis and logrank test were used to estimate the survival. Results: There were statistically significant differences between the groups. RUH had the highest maximal PSA (P-.0000), HDRboost had the highest T stage (P-.03), and both HDR groups had higher Gleason scores (P-.009). Median follow-up for RUH, HDRalone and HDRboost was 19, 16 and 36 months, respectively. HDRboost and RUH were significantly linked with mild gastrointestinal morbidity (P-.02). There were no differences between PSA levels between the groups at the last follow-up. Biochemical disease-free survival at 2 years was better for both HDR groups than RUH (100% vs 96%; P-0.09), however it was not significant. Conclusion: Regimens using radioablative doses per fraction are efficient, while yielding low morbidity. In spite of the necessity of the long-term results, comparison with conventional and/or hypofractionated externalbeam radiation therapy schedules should be performed with further randomized clinical trial design. Author Disclosure: P.A. Wojcieszek: None. M. Szlag: None. G. Glowacki: None. A. Cholewka: None. M. Fijalkowski: None. S. Kellas: None. B. Biala: None. L. Miszczyk: None.
2667 Outcomes and Toxicity for Treatment of Adrenal Metastases With Radiation Therapy W.G.A. Wang,1 K. Sura,1 J. Robertson,1 D.J. Krauss,1 P.Y. Chen,2 and I.S. Grills2; 1Beaumont Health, Royal Oak, MI, 2Beaumont Health System, Royal Oak, MI
E274
International Journal of Radiation Oncology Biology Physics
Purpose/Objective(s): To evaluate local control and toxicity in patients undergoing radiation therapy (RT) for adrenal metastases. Materials/Methods: This is a retrospective review of 26 patients who have undergone radiation therapy for adrenal metastases at our institution from 2008 to 2014. The median RT dose was 35Gy (30-50Gy) in 5 fractions (314). The most common fractionation scheme was 40Gy in 5 fractions. Patients were stratified based on their initial treatment intent. Palliative patients (Pt) (n Z 13) received radiation therapy due to pain and/or rapidly enlarging lesions. Oligometastatic patients (O) (n Z 13) underwent radiation therapy with the goal of slowing disease progression. Local control (LC), distant control (DC), overall survival (OS), and acute/late toxicities were evaluated. Results: The majority of the patients were male (62%) with median age of 66. 62% of patients had a non-small cell lung cancer primary (88% adenocarcinoma, 12% squamous cell carcinoma). 19 patients had left sided, 5 had right sided, and 3 had bilateral tumors. The median BED10 for the cohort was 53.6Gy (range 39-85.5Gy). The median BED10 for the O group was 72Gy (range 72-85.5Gy) and 48Gy (range 39-53.6Gy) for the Pt group. The dose range for the two groups did not overlap. The mean GTV was 58cm3. The average mean doses to the liver, kidney, and stomach for the O group were 4.2 Gy, 9.2 Gy, and 9.4 Gy respectively. The average duodenum maximum dose was 35Gy for the O group. Deliverable BED in O cases was dependent on adjacent normal tissue tolerance. Median OS for the entire cohort was 16 months. The 1/2 year OS for the cohort was 56%/26%. The 1/2 year OS was 79%/40% for the O group and 27%/9% for the Pt group (P Z 0.004). The 1 year DC was 14% for the O group and 8% for the Pt group. The 1/2 year LC for the cohort was 74%/43%. The 1/2 year LC was 81/54% for the O group and 67/0% for the Pt group (P Z 0.04). 9 out of 13 patients (70%) in the Pt group had improvement in their pain after RT. Treatments were well tolerated with 8 acute grade 1 nausea and only 1 acute grade 2 nausea/ vomiting. One patient who received bilateral adrenal treatment did develop grade 2 adrenal insufficiency as a late toxicity. Another patient may have developed an inflammatory/immune reaction with RT and nivolumab. He developed severe abdominal pain with diarrhea and died shortly after. Lack of documented GI toxicity limits dosimetric analyses for correlation. Conclusion: RT or SBRT was safely delivered to adrenal metastases and achieved palliative benefit in 70% of the patients. Local control may be limited by safely deliverable doses given adjacent stomach and small bowel, with an optimal BED to be determined. Prospective trials are required to evaluate the potential role for cure or prolonged progressionfree survival after SBRT for oligometastases. Author Disclosure: W.A. Wang: None. K. Sura: None. J. Robertson: None. D.J. Krauss: None. P.Y. Chen: Stock; Greater Michigan Gamma Knife. I.S. Grills: Stock; Greater Michigan Gamma knife. on the board of directors; Greater Michigan Gamma knife.
proton therapy at our institution. All 14 patients were planned with three-dimensional conformal proton therapy (3D-CPT) using two parallel opposed fields as well as comparison IMRT plans. A rectal balloon filled with water was used in all patients treated. Prescribed dose to the prostate was 79.2 Gy cobalt Gy equivalent (CBE). Dosevolume histograms were compared between the treatment plans. The Lyman-Kutcher-Burman model (n Z 0.09, m Z 0.13, and TD50 Z 76.9 Gy) was used to generate NTCP estimates for both IMRT and proton plans. Results: At least 95% of the planning target volume received the prescription dose for both proton and IMRT plans. Dose constraints placed on the rectum included volume receiving 65 Gy (V65) less than 17% and V40 less than 35%. The mean dose to the rectum was 24.8 Gy (range, 19.2-30.1 Gy) and 31.5 Gy (range, 23.7-39.4 Gy) for the proton and IMRT plans, respectively. The V65 constraint was unachievable in 3 of the proton plans and 3 of the IMRT plans. The mean V70 and V75 for proton plans were 8.7% and 5.7% compared to 7.4% and 4.9% for the IMRT plans. The mean NTCP for proton treatment plans was 7.7% (range, 2.7-11.7%) and 7.9% (range, 1.7-15.7%) for IMRT (P Z 0.46). After median follow-up of 9 months, no grade 2 or higher toxicity has been reported. Conclusion: Utilizing NTCP estimations, 3D-CPT proton therapy and IMRT have similar predicted rates of rectal toxicity. Currently, a Phase III randomized clinical trial is underway comparing proton therapy and IMRT with regards to rectal toxicity and quality of life. Author Disclosure: B.W. Fischer-Valuck: None. T.R. Mazur: None. H.A. Gay: None. L.A. Olsen: None. M.B. Altman: None. J.M. Michalski: None.
2668 A Treatment Planning Comparison of Proton Therapy and Intensity Modulated Radiation Therapy (IMRT) for Prostate Cancer Using the Normal Tissue Complication Probability (NTCP) B.W. Fischer-Valuck, T.R. Mazur, H.A. Gay, L.A. Olsen, M.B. Altman, and J.M. Michalski; Washington University School of Medicine, St. Louis, MO Purpose/Objective(s): The volume of rectum receiving high-dose radiation therapy (i.e. > or Z 60 Gy) is consistently associated with the risk of Grade > or Z 2 rectal toxicity, or rectal bleeding, based on common terminology criteria for adverse events (CTCAE). Our goal was to compare intensity-modulated photon radiation therapy (IMRT) with proton radiation therapy in regard to the rectal dose using the normal tissue complication probability (NTCP). Materials/Methods: All patients between July 2014 and January 2016 were enrolled on a prospective registry, and the first 14 consecutive low or intermediate risk prostate cancer patients were treated with
2669 Changes in Serum Testosterone 60 Months After Proton Therapy for Localized Prostate Cancer R.C. Nichols,1 C.G. Morris,1 C.M. Bryant,1 B.S. Hoppe,1 R.H. Henderson,1 W.M. Mendenhall,1 Z. Li,1 J.A. Costa,2 C.R. Williams,2 and N.P. Mendenhall1; 1University of Florida Health Proton Therapy Institute, Jacksonville, FL, 2Division of Urology University of Florida Health, Jacksonville, FL Purpose/Objective(s): Five studies (1-5) in the contemporary radiation therapy literature have demonstrated a +/-10% decline in Serum Testosterone (ST) for patients receiving x-ray therapy for prostate cancer e presumably due to scatter radiation to the testicular Leydig cells. Materials/Methods: Between August 2006 and October 2011, 399 patients with low and intermediate risk prostate cancer were enrolled on 3 prospective trials delivering between 70 Cobalt Gray Equivalent (CGE) and 82CGE at between 2CGE and 2.5CGE per fraction using passively scattered protons. Serum testosterone (ST) was to be checked at baseline and every 6 months after PT. ST was checked at baseline in 393 patients and at 60 months or later in 169 of these patients (who are the subject for this analysis). The analysis excluded 14 patients who received LHRH agonist therapy before PT and 2 patients who acknowledged taking exogenous testosterone medications after PT. Results: Median baseline ST for the analyzable patients was 374.4 ng/dl (range 120.1 to 791.0). Median ST 5 years after PT was 390.0 ng/dl (range 25.0 to 862.0). The difference was not statistically significant (P Z 0.9931). Conclusion: Passively scattered proton therapy was not associated with testosterone suppression 5 years after PT e suggesting that protons may be associated with less out of field scatter radiation compared with x-rays. Author Disclosure: R.C. Nichols: None. C.G. Morris: None. C.M. Bryant: None. B.S. Hoppe: None. R.H. Henderson: None. W.M. Mendenhall: None. Z. Li: None. J.A. Costa: None. C.R. Williams: None. N.P. Mendenhall: None.