SUMMARY

The dosimetric properties of several new forms of spatially fractionated radiation therapy, commonly referred to as SFRT or GRID; small beam electron GRID, radioisotope-based photon minibeam GRID, and megavoltage photon minibeam GRID were studied. For each methodology, a combination of Monte Carlo simulation (using the Monte Carlo code MCNP6) and physical measurements (using EBT3 radiochromic film) was used to characterize the dose rate and peak to valley dose ratio of each of the proposed methods. The calculated and/or measured dose distributions from each of these new modalities is shown. Beam definition similar to or exceeding that of clinically used GRID therapy techniques, as defined by the peak-to-valley-ratio was achieved for all cases. In addition, for the photon-based minibeam modalities beams below 5 mm in diameter were effectively produced, which could improve healthy tissue recovery. The limitations of each of these techniques are also discussed, namely the reduced dose rate that corresponds to the small beam size. However, each method has some conditions under which it can effectively be used, and with further development in specified areas, aspects of this work could be applied clinically.