Robust optimization of VMAT for prostate cancer accounting for geometric uncertainty

Abstract

The aim of this study was to propose optimal robust planning by comparing the robustness with setup error with the robustness of a conventional planning target volume (PTV)-based plan and to compare the robust plan to the PTV-based plan for the target and organ at risk (OAR). Data from 13 patients with intermediate-to-high-risk localized prostate cancer who did not have T3b disease were analyzed. The dose distribution under multiple setup error scenarios was assessed using a conventional PTV-based plan. The clinical target volume (CTV) and OAR dose in moving coordinates were used for the dose constraint with the robust plan. The hybrid robust plan added the dose constraint of the PTV-rectum to the static coordinate system. When the isocenter was shifted by 10 mm in the superior-inferior direction and 8 mm in the right-left and anterior directions, the doses to the CTV, bladder, and rectum of the PTVbased plan, robust plan, and hybrid robust plan were compared. For the CTV D 99% in the PTV-based plan and hybrid robust plan, over 95% of the prescribed dose was secured in all directions, except in the inferior direction. There was no significant difference between the PTV-based plan and the hybrid robust plan for rectum V 70Gy , V 60Gy , and V 40Gy . This study proposed an optimization method for patients with prostate cancer. When the setup error occurred within the PTV margin, the dose robustness of the CTV for the hybrid robust plan was higher than that of the PTV-based plan, while maintaining the equivalent OAR dose.

Physical and Radiobiological Evaluation of Patient Setup Errors in the Radiotherapy Procedure for Prostate Cancer

“…In literature, some works were focused on the dosimetric or radiobiological assessment of systematic isocenter shift errors for different types of cancers. [17,18,24]. This work aimed to evaluate both the dosimetric and radiobiological effects of the random setup error that usually occurs during the position of prostate patients.…”

A robust treatment planning approach for chest motion in postmastectomy chest wall intensity modulated radiation therapy

“…19,20 Several studies have reported on the effectiveness of robust planning. [21][22][23] Miura et al performed robust planning for laryngeal cancer cases and reported a better clinical target volume (CTV) coverage with the robust plan with a setup error. 21 Wada et al used robust planning for patients with prostate cancer and reported improved CTV coverage at acceptable OAR doses, even with setup errors.…”

“…21 Wada et al used robust planning for patients with prostate cancer and reported improved CTV coverage at acceptable OAR doses, even with setup errors. 22 Therefore, robust planning can be considered a beneficial technique for making treatment plans robust against setup errors. We hypothesized that a PMRT treatment plan with IMRT that is robust against chest wall movement, including respiratory movement, can be created by setting the expected chest wall movement as the setup error during robust optimization.…”

“…Robust planning, which is an optimization method that considers setup errors and reduces change in dose distribution, has attracted attention in recent years 19,20 . Several studies have reported on the effectiveness of robust planning 21–23 . Miura et al.…”

“…Wada et al. used robust planning for patients with prostate cancer and reported improved CTV coverage at acceptable OAR doses, even with setup errors 22 . Therefore, robust planning can be considered a beneficial technique for making treatment plans robust against setup errors.…”