Investigation of Optimal Physical Parameters for Precise Proton Irradiation of Orthotopic Tumors in Small Animals.

Abstract

PURPOSE: The lack of evidence of biomarkers identifying patients who would&#xa0;benefit from proton therapy has driven the emergence of preclinical proton irradiation platforms using advanced small-animal models to mimic clinical therapeutic conditions. This study aimed to determine the optimal physical parameters of the proton beam with a high radiation targeting accuracy, considering small-animal tumors can reach millimetric dimensions at a maximum depth of about 2&#xa0;cm. METHODS AND MATERIALS: Several treatment plans, simulated using Geant4, were generated with different proton beam features to assess the optimal physical parameters for small-volume irradiations. The quality of each treatment plan was estimated by dose-volume histograms and gamma index maps. RESULTS: Because of its low-energy straggling, low-energy proton (<50&#xa0;MeV) single-field irradiation can generate homogeneous spread-out Bragg peaks to deliver a uniform dose in millimeter-sized tumors, while sparing healthy tissues located within or near the target volume. However, multifield irradiation can limit the dose delivered in critical structures surrounding the target for attenuated high-energy beams (E&#xa0;>&#xa0;160&#xa0;MeV). CONCLUSION: Low-energy proton beam platforms are suitable for precision irradiation for translational radiobiology studies.