Collimator design for experimental minibeam radiation therapy

Purpose: To design and optimize a minibeam collimator for minibeam radiation therapy studies using a 250 kVp x‐ray machine as a simulated synchrotron source. Methods: A Philips RT250 orthovoltage x‐ray machine was modeled using the EGSnrc/BEAMnrc Monte Carlo software. The resulting machine model was coupled to a model of a minibeam collimator with a beam aperture of 1 mm. Interaperture spacing and collimator thickness were varied to produce a minibeam with the desired peak‐to‐valley ratio. Results: Proper design of a minibeam collimator with Monte Carlo methods requires detailed knowledge of the x‐ray source setup. For a cathode‐ray tube source, the beam spot size, target angle, and source shielding all determine the final valley‐to‐peak dose ratio. Conclusions: A minibeam collimator setup was created, which can deliver a 30 Gy peak dose minibeam radiation therapy treatment at depths less than 1 cm with a valley‐to‐peak dose ratio on the order of 23%.