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

ByongYong Yi; Sina Mossahebi; Arezoo Modiri; Elizabeth M Nichols; Mariana Guerrero; Narottam Lamichhane; Pranshu Mohindra

doi:10.14338/IJPT-22-00013.1

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

Int J Part Ther. 2022 Jun 28;9(2):31-39. doi: 10.14338/IJPT-22-00013.1. eCollection 2022 Fall.

Authors

ByongYong Yi^{1

2}, Sina Mossahebi^{1

2}, Arezoo Modiri¹, Elizabeth M Nichols^{1

2}, Mariana Guerrero¹, Narottam Lamichhane¹, Pranshu Mohindra^{1

2}

Affiliations

¹ Department of Radiation Oncology, University of Maryland School of Medicine, MD, USA.
² Proton Treatment Center, Baltimore, MD, USA.

Abstract

Purpose: To investigate whether volumetric-modulated proton arc therapy (VPAT) plans generate comparable doses to organs at risk (OARs) compared with interstitial high-dose-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 cm³; 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_2cm³ 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.

Keywords: interstitial brachytherapy; locally advanced gynecologic cancer; proton arc therapy.