Comparison of Scanning Beam Proton Therapy (SBPT) to Intensity Modulated X-ray Therapy (IMRT) for Postoperative Salvage Treatment of Prostate Cancer Patients

Purpose/Objective(s)To determine if significant normal tissue sparing without sacrificing target coverage can be achieved using scanning beam proton therapy (SBPT) compared to intensity modulated x-ray therapy (IMRT) for prostate cancer patients treated for salvage after prostatectomy.Materials/MethodsEleven patients who were treated with IMRT for a rising PSA after prostatectomy were evaluated in this study. All patients were treated with an endorectal balloon. The clinical tumor volume (CTV) consisted of the prostate and the seminal vesicles beds. SBPT plans were generated with both single field (SFO) and multifield optimization planning (MFO) utilizing a planning tumor volume (PTV) and were compared to the IMRT plans. The PTV consisted of the CTV plus 11 mm margin laterally (7 mm for IMRT), 5 mm posteriorly, and 7 mm anteriorly, posteriorly, and inferiorly. The total dose prescribed was 70 Gray in 2 Gy fractions to the PTV. Dose volume histograms were generated for the rectum, anterior rectal wall, bladder, and pelvis. The anterior rectal wall was defined as a 3 mm layer of rectal tissue encompassing the edge of the anterior half of the rectum. The differences between treatment groups were analyzed using a t-test.ResultsPoster Viewing Abstract 3661; TableComparison of normal tissue doses between IMRT and SBPTRectumIMRTSBPT-SFOSBPT-MFOMean V3048.7 ± 13.1%36.5 ± 9.5%, P <0.0135.1 ± 8.3%, P <0.01Mean V4037.9 ± 11.2%30.0 ± 8.3%, P <0.0128.8 ± 7.3%, P <0.01Mean V6022.1 ± 7.0%17.4 ± 5.5%, P <0.0116.7 ± 5.2%, P <0.01Mean V7010.1 ± 3.4%7.6% ± 3.4%, P <0.018.0 ± 3.6%, P <0.01Anterior Rectal WallMean V3078.8 ± 12.2%70.0 ± 11.7%, P <0.0170.0 ± 11.3%, P <0.01Mean V4072.5 ± 12.7%62.8 ± 11.4%, P <0.0162.9 ± 11.1%, P <0.01Mean V6055.6 ± 11.8%46.7 ± 9.7%, P <0.0147.1 ± 10.0%, P <0.01Mean V7037.2 ± 8.8%29.9% ± 9.6%, P <0.0131.5% ± 10.0%, P <0.01PelvisMean V1022.4 ± 6.7%6.0 ± 1.8%, P <0.016.2 ± 1.9%, P <0.01Mean V2014.8 ± 4.9%4.7 ± 1.4%, P <0.014.9 ± 1.5%, P <0.01 Open table in a new tab ConclusionIn this study, SBPT significantly decreased the dose given to the rectum, anterior rectal wall, and pelvis. PTV coverage was adequate in all cases. There was no significant difference between SFO and MFO proton plans in the doses given to normal tissues. These dosimetric findings suggest that SBPT can be used safely in the salvage treatment of prostate cancer patients after prostatectomy. Prospective studies are needed to determine if the decrease in normal tissue doses can lead to better patient outcomes. Purpose/Objective(s)To determine if significant normal tissue sparing without sacrificing target coverage can be achieved using scanning beam proton therapy (SBPT) compared to intensity modulated x-ray therapy (IMRT) for prostate cancer patients treated for salvage after prostatectomy. To determine if significant normal tissue sparing without sacrificing target coverage can be achieved using scanning beam proton therapy (SBPT) compared to intensity modulated x-ray therapy (IMRT) for prostate cancer patients treated for salvage after prostatectomy. Materials/MethodsEleven patients who were treated with IMRT for a rising PSA after prostatectomy were evaluated in this study. All patients were treated with an endorectal balloon. The clinical tumor volume (CTV) consisted of the prostate and the seminal vesicles beds. SBPT plans were generated with both single field (SFO) and multifield optimization planning (MFO) utilizing a planning tumor volume (PTV) and were compared to the IMRT plans. The PTV consisted of the CTV plus 11 mm margin laterally (7 mm for IMRT), 5 mm posteriorly, and 7 mm anteriorly, posteriorly, and inferiorly. The total dose prescribed was 70 Gray in 2 Gy fractions to the PTV. Dose volume histograms were generated for the rectum, anterior rectal wall, bladder, and pelvis. The anterior rectal wall was defined as a 3 mm layer of rectal tissue encompassing the edge of the anterior half of the rectum. The differences between treatment groups were analyzed using a t-test. Eleven patients who were treated with IMRT for a rising PSA after prostatectomy were evaluated in this study. All patients were treated with an endorectal balloon. The clinical tumor volume (CTV) consisted of the prostate and the seminal vesicles beds. SBPT plans were generated with both single field (SFO) and multifield optimization planning (MFO) utilizing a planning tumor volume (PTV) and were compared to the IMRT plans. The PTV consisted of the CTV plus 11 mm margin laterally (7 mm for IMRT), 5 mm posteriorly, and 7 mm anteriorly, posteriorly, and inferiorly. The total dose prescribed was 70 Gray in 2 Gy fractions to the PTV. Dose volume histograms were generated for the rectum, anterior rectal wall, bladder, and pelvis. The anterior rectal wall was defined as a 3 mm layer of rectal tissue encompassing the edge of the anterior half of the rectum. The differences between treatment groups were analyzed using a t-test. ResultsPoster Viewing Abstract 3661; TableComparison of normal tissue doses between IMRT and SBPTRectumIMRTSBPT-SFOSBPT-MFOMean V3048.7 ± 13.1%36.5 ± 9.5%, P <0.0135.1 ± 8.3%, P <0.01Mean V4037.9 ± 11.2%30.0 ± 8.3%, P <0.0128.8 ± 7.3%, P <0.01Mean V6022.1 ± 7.0%17.4 ± 5.5%, P <0.0116.7 ± 5.2%, P <0.01Mean V7010.1 ± 3.4%7.6% ± 3.4%, P <0.018.0 ± 3.6%, P <0.01Anterior Rectal WallMean V3078.8 ± 12.2%70.0 ± 11.7%, P <0.0170.0 ± 11.3%, P <0.01Mean V4072.5 ± 12.7%62.8 ± 11.4%, P <0.0162.9 ± 11.1%, P <0.01Mean V6055.6 ± 11.8%46.7 ± 9.7%, P <0.0147.1 ± 10.0%, P <0.01Mean V7037.2 ± 8.8%29.9% ± 9.6%, P <0.0131.5% ± 10.0%, P <0.01PelvisMean V1022.4 ± 6.7%6.0 ± 1.8%, P <0.016.2 ± 1.9%, P <0.01Mean V2014.8 ± 4.9%4.7 ± 1.4%, P <0.014.9 ± 1.5%, P <0.01 Open table in a new tab ConclusionIn this study, SBPT significantly decreased the dose given to the rectum, anterior rectal wall, and pelvis. PTV coverage was adequate in all cases. There was no significant difference between SFO and MFO proton plans in the doses given to normal tissues. These dosimetric findings suggest that SBPT can be used safely in the salvage treatment of prostate cancer patients after prostatectomy. Prospective studies are needed to determine if the decrease in normal tissue doses can lead to better patient outcomes. In this study, SBPT significantly decreased the dose given to the rectum, anterior rectal wall, and pelvis. PTV coverage was adequate in all cases. There was no significant difference between SFO and MFO proton plans in the doses given to normal tissues. These dosimetric findings suggest that SBPT can be used safely in the salvage treatment of prostate cancer patients after prostatectomy. Prospective studies are needed to determine if the decrease in normal tissue doses can lead to better patient outcomes.