Robust Optimization for Prostate Radiation Therapy: Assessment of Delivered Dose by Incorporating Intrafraction Prostate Position Deviations

Abstract

Purpose: To assess the robustness of the dose delivered to the clinical target volume (CTV) between planning target volume (PTV)-based and robust optimization planning approaches in localized prostate cancer radiation therapy.

Methods and materials: Retrospective data of 20 patients with prostate cancer, including radiation therapy 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 a 7-mm CTV-PTV margin, whereas robust planning considered same-magnitude position deviations. Differences in CTV dose delivered to 99% volume (D99), PTV dose delivered to 95% volume (D95), and bladder and rectum V40 (volume receiving 40 Gy) and V60 (volume receiving 60 Gy) 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 with PTV-based planning, the mean (standard deviation) 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 (standard deviation) 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), whereas 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.

Conclusions: Robust optimization resulted in lower V40 and V60 values for the bladder compared with PTV-based planning. However, no difference in CTV dose accuracy was found between the 2 approaches.

Figure 1

The prostate position during treatment delivery in (a) left–right and posterior–anterior and (b) superior–inferior and posterior–anterior directions with (green data points) and without (red data points) position correction applied. (A color version of this figure is available at 10.1016/j.adro.2024.101455.)

Figure 2

The difference in CTV, PTV, rectum and bladder DVH metrics between PTV-based and robust planning methods. Abbreviations: CTV = clinical target volume; DVH = dose-volume histogram; PTV = planning target volume. (A color version of this figure is available at 10.1016/j.adro.2024.101455.)

Figure 3

Dose distribution in (a) axial and (b) sagittal planes of the PTV-based plan for a representative case. Corresponding dose distribution in (c) axial and (d) sagittal planes of the robust optimization plan generated for the same representative case. Abbreviations: PTV = planning target volume. (A color version of this figure is available at 10.1016/j.adro.2024.101455.)

Figure 4

The difference between planned and delivered target volumes DVH metrics of plans generated using PTV-based and robust planning methods, with and without position corrections applied. The letters ‘C’ and ‘NC’ represent corrected and not corrected scenarios for position deviations, respectively. Abbreviations: DVH = dose-volume histogram; PTV = planning target volume. (A color version of this figure is available at 10.1016/j.adro.2024.101455.)

Figure 5

The difference between planned and delivered (a) rectum and (b) bladder DVH metrics of plans generated using PTV-based and robust planning methods, with and without position corrections applied. The letters ‘C’ and ‘NC’ represent corrected and not corrected scenarios for position deviations, respectively. Abbreviations: DVH = dose-volume histogram; PTV = planning target volume. (A color version of this figure is available at 10.1016/j.adro.2024.101455.)