TH‐C‐204B‐02: Monte Carlo Feasibility Study of a Compact Microbeam Small Animal Irradiator

Purpose : Microbeam radiation therapy (MRT) is a promising but poorly understood experimental treatment modality. As an alternative to synchrotron‐based facilities we propose a compact carbon nanotube‐based MRT device for small animal research. We report on a Monte Carlo‐based feasibility study of the proposed design. Method and Materials : Monte Carlo calculations were performed using EGSnrc‐based codes. The proposed device design includes a carbon nanotube cathode shaped to match the collimator aperture a reflection anode with filter and a microbeam collimator. The collimator is sized to deliver a beam width ranging from 30–200 microns at 15 cm SAD. Design parameters studied with Monte Carlo include electron energy anode angle filtration and collimator design. Results : Increasing the energy from 100 kVp to 150 kVp increased the photon fluence through the collimator by a factor of 1.7. Both energies produced a largely uniform fluence along the microbeam with 5% decreases in intensity near the edges of the long dimension. The isocentric dose rate for 150 kVp was calculated to be 1200 Gy/min/A in the center of a 3 cm diameter target. Expected cathode currents of 1 A project an isocentric dose rate of 80 Gy/sec for a four‐beam system. Scatter contributions resulting from collimator size were found to produce only small (<7%) changes in the dose rate for field widths greater than 50 microns. Dose vs. depth was weakly dependant on filtration material. The peak‐to‐valley ratio outside the beam was less than 0.5% indicating the valley dose between adjacent microbeams will be no more than 1% of the peak dose. Conclusion : Monte Carlo simulations demonstrate that the proposed microbeam device will be capable of delivering a sufficient dose rate and peak‐to‐valley‐ratio to be useful for small‐animal MRT studies. Conflict of interest : The work is supported by NIH grant 1RC2CA148487‐01