Intensity-modulated radiotherapy for whole pelvis irradiation in prostate cancer: A dosimetric and plan robustness study between photons and protons. (June 2018)

• Record Type: Journal Article
• Authors: Ong, Ashley L.K.; Ang, K.W.; Master, Zubin; Wong, Sharon M.M.; Tuan, Jeffrey K.L.
• Is Part Of: Technical innovations & patient support in radiation oncology. Volume 6(2018)
• Page Start: 11
• Page End: 19
• Publication Date: 2018-06
• Subjects: Prostate cancer -- Pelvic lymph nodes -- VMAT -- IMPT -- PBS -- Robust analysis; Radiotherapy -- Periodicals; Cancer -- Radiotherapy -- Periodicals; Cancer -- Patients -- Hospital care -- Periodicals; 615.842
• DOI: 10.1016/j.tipsro.2018.02.001
• Languages: English
• ISSNs: 2405-6324

Abstract

Highlights: A split target method was proposed in prostate with pelvic lymph nodes irradiation. Pencil beam scanning (PBS) plans were able to achieve optimal target coverage. Low to intermediate dose to the organs at risk were reduced in PBS plans. PBS plans remained robust in simulated setup and range errors analysis. Abstract: Purpose: To evaluate the dosimetric impact and plan robustness of using Pencil Beam Scanning (PBS) in patients that requires prophylactic pelvic lymph nodes (PLNs) irradiation for prostate cancer. Material and methods: Five intermediate to high-risk prostate patients previously treated using volumetric modulated arc therapy (VMAT), were selected for this study. Comparative proton radiotherapy plans were generated, where a three-field intensity modulated proton therapy (IMPT) plan was for the phase 1 planning target volume (PTV1) with PLNs. A technique with two posterior oblique fields using single field uniform dose (SFUD) was used for phase 2 (PTV2) volume, that comprises of the prostate and proximal seminal vesicles (Pro + proxSVs). Plan evaluation was performed on PTV coverage and dose to the organs at risk (OARs) using VMAT plans as a baseline (BL). Robust analysis on clinical target volume (CTV) coverage for the PBS plans was simulated with a 3 and 5 mm setup errors and a 3.5% range uncertainty. Results: For target coverage, PTV1 and PTV2 showed negligible differences with a comparable homogeneity index (HI) values for both modalities. Proton plans produced a statistically significant lower mean dose to the bladder (32.5 Gy(RBE) vs. 46.5 Gy) and rectum (33.6 Gy(RBE) vs. 42.7 Gy). Dose to the bladder and rectum was equivalent at the high dose region. For the bowel cavity, the mean dose for proton plans were 45% lower compared to VMAT plans. Similarly, proton plans were able to achieve an overall reduction in integral dose for both treatment phase. CTV coverage remained high with all the simulated setup and range errors. Conclusions: Proposed beam geometries for PTV1 and PTV2 proton plans presented good treatment accuracy with similar target coverage as the VMAT plans. Better sparing of OARs was achieved at the low-medium dose region for the proton plans.