SU‐E‐T‐528: Beam Model Interface for Treatment Planning in Proton Therapy Using Macro Monte Carlo

Purpose: A previously developed macro Monte Carlo (MC) method for accurate and efficient dose calculations in proton radiotherapy is interfaced with a beam model in order to allow treatment planning for proton beams. Methods: The beam model interface generates particles above the beam modifiers such as block or range shifter plates for the macro MC algorithm and is based on an already existing beam model for modulated scanning beam lines. Based on the beam data of the commissioned beam model and the patient treatment plan, a sampling procedure is defined in order to provide the particle type, position, direction, energy and weight of the starting particle necessary for the macro MC transport through the beam modifiers and for the dose calculation. The new interface is validated by comparing sampled position and energy distributions of single spots with those from the already existing beam model. Furthermore, dose distributions in a water phantom for single spots of different energies calculated using either the new interface with the macro MC or the pencil beam algorithm available in Eclipse are compared. Results: The sampled distributions for the position within a spot as well as the energy distributions are in good agreement with the corresponding distributions of the already existing beam model. The ranges of the depth dose curves for the calculated dose distributions agree within 1 mm, while the dose differences are generally within 2% except close to the phantom surface where the pencil beam overestimates the macro MC dose by 3%. Conclusion: By interfacing a beam model with the macro MC dose calculation algorithm accurate treatment planning for proton radiation therapy beams is realized. This work was supported by Varian Medical Systems. This work was supported by Varian Medical Systems.