Robust optimization for prostate radiotherapy: Assessment of delivered dose by incorporating intrafraction prostate position deviations

Abstract

Aim To assess the robustness of the dose delivered to the clinical target volume (CTV) using planning target volume (PTV) based and robust optimization planning approaches in localized prostate cancer radiotherapy. Methods Retrospective data of twenty prostate cancer patients, including radiotherapy and real-time prostate position, were analyzed. Two sets of volumetric modulated arc therapy plans were generated per patient: PTV-based and robust optimization. PTV-based planning used 7mm CTV-PTV margin, while robust planning considered same-magnitude position deviations. Differences in CTV D99, PTV D95, bladder and rectum V40, and V60 values were evaluated. The target position, determined by in-house position monitoring system, was incorporated for dose assessment with and without position deviation correction. Results In the robust optimization approach, compared to PTV-based planning, the mean (SD) V40 and V60 values of the bladder were reduced by 5.2% (4.1%) and 5.1% (1.9%), respectively. Similarly, for the rectum, the reductions were 0.8% (0.5%) and 0.6% (0.6%). In corrected treatment scenarios, both planning approaches resulted in a mean (SD) CTV D99 difference of 0.1 Gy (0.1 Gy). In the not corrected scenario, PTV-based planning reduced CTV D99 by 0.1 Gy (0.5 Gy), while robust planning reduced it by 0.2 Gy (0.6 Gy). There was no statistically significant difference observed in the planned and delivered rectum and bladder dose for both corrected and not corrected scenarios. Conclusion Robust optimization resulted in lower V40 and V60 values for the bladder compared to PTV-based planning. However, no difference in CTV dose accuracy was found between the two approaches.