SUMMARY

Minibeam therapy is a current hot topic in radiation therapy with protons. This study proposes a more economical alternative to proton minibeam therapy by using conventional linear accelerator (LINAC)-based megavoltage photon beams. A previous author [Cranmer-Sargison 2015] developed a planar-type (1-D) minibeam collimator for LINACs. A 2-dimensional hexagonal (honeycomb) mesh of minibeams is believed to provide a higher therapeutic advantage. The honeycomb grid pattern has been physically achieved on a conventional linear accelerator for conventional GRID therapy (≥ 1cm holes), but not for minibeams with hole diameter of 3mm or less. This proposal is to optimize the multiple variables which affect the quality of low-MV energy photon minibeam dose distributions on linear accelerators. Variables that affect the quality of the minibeam pattern include the choice of reasonable low-MV beam energies from 2.5 MV-FFF, 3.5 MV-FFF, 4MV and 6 MV-FFF, the diameter and center-to-center spacing of the hexagonal grid, the field size, the collimator hole shape (governed by the manufacturing process), the collimator material and collimator thickness. We hypothesize that "independent" photon sources collimated using an SRS cone will produce a higher GRID quality compared to a conventional broad-beam GRID collimator. A comparison of conventional GRID collimators against minibeam-GRID using the SRS cone method is presented along with a computer program which applies "black-box" optimization to Monte Carlo dose calculations in TOPAS.