SU‐E‐T‐127: Dosimetric Evaluation Microbeam Treatment Method Using Monoenergetic Photon Î1/4‐Beams

Purpose: One of the external radiotherapy techniques with potential to greatly enhance the therapeutic ratio is Microbeam Radiotherapy (MRT). A recent approach to MRT delivers discrete finely spaced μ‐beams. The technique is based on two principles: a] there is almost no dose between the dose peaks of two neighboring μ‐beams and b] it is not needed for the whole target to be irradiated to achieve tumor control. Preliminary results have shown the ability to increase tumor control without increasing normal tissue complication probability with this technique. The purpose of this study was to dosimetrically evaluate the clinical feasibility of the above concept, taking into consideration factors as beam energy, size, and separation, and tumor depth. Methods: A Monte Carlo (MC) model was used to simulate different configurations of μ‐beams. A total of 420 different μ‐beams were evaluated for beam sizes, energies, depths and distances between the beams. The different MC beam penetration results were compared vs. simulations, which were conducted at the existing Small animal irradiator (SARRP) facility at our department. Results: Separation between the peak doses of the μ‐beams was well maintained in all simulations. This shows that the scatter can be ignored even for cases where the distance from the center of the μ‐beams was set to 200 μm (E = 100 keV) and for depths as great as 5 cm. Monoenergetic 100 keV μ‐beam energies were ∼25% more penetrative than a 220 kVp SARRP beam at the depth of 8 cm. The effect is more profound as the energy increases. Conclusion: Dosimetric evaluation of this MRT method showed it could feasibly be used to treat tumors at clinically relevant depths. MC results showed that the scatter between the beams remains minimal even for depths of 5 cm and separation of the beams of 200 μm.