Dosimetric Study of Proton Therapy Using Scanning Method for Localized Prostate Cancer Patients in Comparison With Wobbler Method and Volumetric-Modulated Arc Therapy

Abstract

<h3>Purpose/Objective(s)</h3> Proton therapy (PT) for localized prostate cancer using the wobbler method (passive scattering) has been reported to have favorable biochemical control and late toxicities rates. In recent years, PT has been gradually shifting to scanning methods from wobbler methods. We performed a planning study to compare the dose distribution of the scanning method with that of the wobbler and the volumetric modulated arc therapy (VMAT) for patients with localized prostate cancer. <h3>Materials/Methods</h3> Thirty prostate cancer patients treated in 2016-2018 were randomly selected. Three radiotherapy plans were created for each patient with the same prescribed dose (76.0 Gy or Gy [RBE] in 38 fractions) and compared using dose-volume histograms. Dose constraints were clinical target volume (CTV) D98 ≥ 73.0 Gy (RBE), rectal wall V65 < 17%, V40 < 35%, and bladder wall V65 < 25% and V40 < 50%, respectively. CTV doses, bladder and rectum wall dose volumes (V10 - V75), Dmean, and Dmax were calculated and tested by Wilcoxon's rank-sum test. <i>P</i> < 0.05 was determined to be statistically significant. <h3>Results</h3> The dose coverage of CTV was favorable with the scanning and the wobbler than with the VMAT. Wide ranges of the rectal and bladder wall volumes of V10 - V70 were significantly lower with the scanning method compared with the wobbler method and the VMAT (<i>P</i> < 0.05). The wobbler method yielded better dose distribution of the rectum and bladder wall in the low dose range (V10-20) and near the maximum dose compared with the VMAT. <h3>Conclusion</h3> Compared with the wobbler method and the VMAT, the scanning method enables further reduction of the rectal and bladder doses while maintaining the CTV dose.