# Dosimetric Feasibility of Dose-Painting Radiation Therapy for Targeting Hypoxia in Prostate Cancer on a Novel Ring Gantry Radiation Therapy System

## TL;DR

This study shows that a new radiation therapy system can safely increase doses to hypoxic areas in prostate cancer tumors.

## Contribution

The novel ring gantry system enables dose-painting to hypoxic regions in prostate cancer while protecting surrounding organs.

## Key findings

- Prescribed doses were successfully delivered to both tumor and hypoxic regions in all seven patients.
- Dose escalation was achieved without exceeding organ-at-risk dose limits.
- Three different fractionation schemes were tested and found to be dosimetrically feasible.

## Abstract

Hypoxia is a well-known major factor contributing to the radioresistance of prostate cancer, which could be counteracted by increasing the dose. This study aimed to demonstrate the dosimetric feasibility of a dose-painting radiation therapy plan for prostate cancer, using a novel ring gantry system, based on the localization of tumoral and hypoxic areas.

Seven patients from the Programme d’Action Intégré de Recherche-prostate study, who underwent external-beam radiation therapy for intermediate-risk prostate cancer and exhibited pretherapeutic fluromisonodazole positron emission tomography (PET) uptake in the tumor, were selected. The gross tumor volume (GTV) was delineated on the magnetic resonance imaging, and the hypoxic region within the planning target volume was delineated based on fluromisonodazole PET uptake. Intensity modulated radiation therapy planning was performed based on 3 different prescriptions: standard fractionation (77 Gy in 35 fractions to the planning target volume), with an integrated boost of 95 Gy and 118 Gy in 35 fractions to the GTV and the hypoxic region, moderate hypofractionation (60 Gy in 20 fractions) with a boost of 67 Gy and 91 Gy to the GTV and the hypoxic region, and high hypofractionation (40 Gy in 5 fractions) with a boost of 50 Gy to the GTV and as high as possible to the hypoxic region. Planning was performed on the research version of the RefleXion treatment planning system.

We achieved the prescribed dose in all 7 patients while respecting the usual dose limits for organs at risk.

This study demonstrated the dosimetric feasibility of dose escalation in both the tumor and hypoxic regions in patients with prostate cancer using the RefleXion treatment planning system, without compromising the dose limits for organs at risks.