Investigation of optimal physical parameters for precise proton irradiation of orthotopic tumors in small animals.

PURPOSE: The lack of evidence of biomarkers identifying patients that would 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 aims to determine the optimal physical parameters of the proton beam with a high radiation targeting accuracy, since small-animal tumors can reach millimetric dimensions at a maximum depth of about 2 cm.

MATERIAL AND METHODS: 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: Due to low energy straggling, low energy proton (<50 MeV) single-field irradiation can generate homogeneous SOBP to deliver a uniform dose in millimeter-sized tumors, while sparing healthy tissues located within or near the target volume. However, multi-field irradiation can limit the dose delivered in critical structures surrounding the target for attenuated high energy beams (E>160 MeV).

CONCLUSION: Low energy proton beam platforms are suitable for precision irradiation for translational radiobiology studies.