Proton Arc Therapy vs Interstitial HDR Brachytherapy in Gynecologic Cancer with Parametrial/pelvic Side Wall Extension

Purpose: To investigate whether volumetric-modulated proton arc therapy (VPAT) plans generate comparable doses to organs at risk (OARs) compared with interstitial highdose-rate (iHDR) brachytherapy for patients with gynecologic cancer with disease extension to parametrial/pelvic side wall, who are not eligible for the aggressive procedure. Materials and Methods: VPAT delivers proton arc beams by modulated energies at the beam nozzle while maintaining the same incident energy to the gantry during the arc rotation. Plans of 10 patients previously treated with iHDR brachytherapy for high-risk clinical treatment volumes (HRCTV; 31.8-110.6 cm(3); lateral dimensions, 4.2-5.6 cm) were selected and compared with VPAT plans. VPAT plans for each patient were designed using a 152- to 245-MeV range of energy-modulated proton beams. Results: HRCTV coverage of the VPAT plans was comparable to that of the iHDR plans, with V150% showing no statistical differences. On average, the V100% and V90% of VPAT plans were higher than those of the iHDR plans, 95.0% vs 91.9% (P =.02) and 98.6% vs 97.5% (P =.02), respectively. D100 was also 17% higher for the VPAT plans (P =.03). On average, the D-2cm(3) of bladder, rectum, and small bowels in the VPAT plans were considerably lower than those in iHDR plans (by 17.4%, 35.2%, and 65.6%, respectively; P,.05 for all OARs). Conclusion: VPAT-generated plans were dosimetrically superior to those with HDR brachytherapy with interstitial needles for locally advanced gynecologic cancer with parametrial/pelvic side wall disease extension. Dosimetrically, VPAT provides a noninvasive alternative to iHDR brachytherapy with a superior dosimetric profile.

Automated summary

This study compared the dosimetric results of volumetric-modulated proton arc therapy (VPAT) with interstitial high-dose-rate (iHDR) brachytherapy for gynecologic cancer patients. The results showed that the HRCTV coverage of VPAT plans was comparable to iHDR plans, but VPAT plans had higher V100% and V90% and D100 values. Additionally, VPAT plans showed advantages in reducing doses to the bladder, rectum, and small bowels.