Proton Minibeam Radiation Therapy and Arc Therapy: Proof of Concept of a Winning Alliance

Abstract

(1) Background: Proton Arc Therapy and Proton Minibeam Radiation Therapy are two novel therapeutic approaches with the potential to lower the normal tissue complication probability, widening the therapeutic window for radioresistant tumors. While the benefits of both modalities have been individually evaluated, their combination and its potential advantages are being assessed in this proof-of-concept study for the first time. (2) Methods: Monte Carlo simulations were employed to evaluate the dose and LET distributions in brain tumor irradiations. (3) Results: a net reduction in the dose to normal tissues (up to 90%), and the preservation of the spatial fractionation of the dose were achieved for all configurations evaluated. Additionally, Proton Minibeam Arc Therapy (pMBAT) reduces the volumes exposed to high-dose and high-LET values at expense of increased low-dose and intermediate-LET values. (4) Conclusions: pMBAT enhances the individual benefits of proton minibeams while keeping those of conventional proton arc therapy. These results might facilitate the path towards patients’ treatments since lower peak doses in normal tissues would be needed than in the case of a single array of proton minibeams.

Proton minibeam radiation therapy for treating metastases: A treatment plan study

“…Our pMBRT simulations had been previously calibrated and benchmarked against experimental data in water phantoms 43,44,46 . The global uncertainty, defined as the average statistical uncertainty of voxels with a dose higher than 90% of the maximum dose, was below 3%, as considered in similar works on pMBRT 33,35 …”

“…The pencil beam scanning (PBS) spot configuration of PT and pMBRT plans was created by the ECLIPSE treatment planning system (Varian Medical Systems, Palo Alto, CA, USA) using the Nonlinear Universal Proton Optimized algorithm (NUPO) (v.15.6.05) with PBS algorithm and delivery. The optimization was performed considering seamless irradiations as in other recent studies 33,35 …”

“…43,44,46 The global uncertainty, defined as the average statistical uncertainty of voxels with a dose higher than 90% of the maximum dose, was below 3%, as considered in similar works on pMBRT. 33,35…”

“…TOPAS simulations were performed using a physic list built with the Geant4_Modular option and modules recommended for proton therapy ("g4em-standard_opt3" "g4h-phy_QGSP_BIC" "g4decay" "g4ion-binarycascade" "g4h-elastic_HP" "g4stopping" "g4radioactivedecay"), 45 as in other pMBRT studies. 33,35 The production threshold for secondary particles, that is, the range cut for all particles, was set at 0.01 mm, and the dose-scoring grid resolution was 0.5 × 0.5 × 0.5 mm 3 . All other parameters used default options.…”