Room: Karl Dean Ballroom A1
Purpose: To optimize the design of a multi-slit collimator (MSC) that will enable microbeam therapy (MRT) on the small animal radiation research platform (SARRP). The effects of various MSC and beam parameters on key performance metrics are used to inform the design of a divergent MSC prototype.
Methods: A validated Monte Carlo (MC) model of the SARRP was adopted for use in simulating an MRT delivery scheme with the 1x1 cmÂ² nozzle. MC data were used to optimize a subset of MSC and beam parameters in an effort to maximize the peak-to-valley dose ratio (PVDR) and minimize the full-width at half-maximum (FWHM) of the fractionated dose distributions. The effect of the MSC on entrance dose rate relative to the 1x1cmÂ² treatment field was also considered for the small focal spot. Preliminary experimental work was completed using a parallel-slit steel collimator with the 220kV treatment beam. EBT3 film dose measurements were acquired for depths between 0 and 2.1cm in solid water, at two collimator-to-surface distances (CSD), and compared with the results of our MC simulations.
Results: MRT dose distributions were compared for various choices of slit width, collimator thickness, focal spot (FS) size and construction material across three candidate beam energies (220, 80 and 40kVp). Use of the 220kVp beam and small FS maximized the PVDR and decreased its sensitivity to modest changes in CSD, but resulted in lower dose rates and increased the sensitivity to slit size. Early experimental work has reaffirmed the challenges of producing a regular array of microbeams and underscores the need for a more precise, divergent collimator.
Conclusion: Monte Carlo simulations have enabled us to optimize, within physically reasonable constraints, the relevant design parameters of a theoretical MSC. Construction of a prototype MSC has benefitted from the evaluation of the simulated results and preliminary parallel-slit experiments.