LAUSR

Motivation/objective Intraoperative Radiation Therapy with low energy X-rays (XIORT) is largely used in oncology (ex: INTRABEAM®, Carl Zeiss), and could benefit from a dose calculation tool. A high level of accuracy is reached with Monte Carlo (MC) simulations, however it is a time-consuming technique and consequently it is not suitable for real-time dose planning of a XIORT treatment. This work presents a dose calculation algorithm based in MC phase-space information to compute dose distributions for the INTRABEAM device within minutes, fully taking into account the different structures of the patient. Materials and methods The Hybrid Monte Carlo (HMC) code takes into account the photoelectric and the Compton effects for X-rays up to 50 keV. The tissue assignation from the CT numbers is done following the method described in [1] for 24 different materials. Savings in computation time are possible by taking some variance reduction techniques to the extreme, such as the use of meta-histories, each one representing the fate of many particles, or dose normalization, which allows statistic noise-free dose distributions with a low number of initial meta-histories. Detailed MC simulations have been generated with penEasy [2] to validate our tool in homogeneous and heterogeneous conditions with the different INTRABEAM applicators. Results Dose distributions computed by the HMC are in good agreement (2%–1 mm) with penEasy detailed simulations in homogeneous and heterogeneous media. Accurate dose distributions were obtained with the HMC in 5 min a single core of a modern PC ([email protected] GHz), compared to 10 days simulation with penEasy. Conclusion The HMC provides accurate dose distributions within minutes. Its high speed allows an on-the-fly dose calculation which includes the realistic effects of the beam in patient voxelized geometries.