Author: Hao Gao, Wangyao Li, Yuting Lin, Chao Wang, Wei Wu ðĻâðŽ
Affiliation: Institute of Modern Physics, Chinese Academy of Sciences, Department of Radiation Oncology, University of Kansas Medical Center ð
Purpose: Proton minibeam radiation therapy (pMBRT) delivers a unique peak-and-valley dose pattern using collimators with narrow slits, offering improved normal tissue sparing compared to conventional proton therapy (CONV). However, the dose matrix calculations for pMBRT, due to its submillimeter beam size and complex scattering dynamics, poses a barrier to clinical implementation. This study aims to develop a fast, semi-analytic algorithm for efficient and accurate dose calculations in pMBRT, enabling its seamless integration into treatment planning workflows.
Methods: According to Fermi-Eyes theory, the initial conditions are required to solve the distribution equation of the phase function of protons. Protons were classified into two categories based on interactions with collimator: (1) pristine protons, which pass through the collimator unaltered. Its corresponding initial condition is a truncated two-dimensional Gaussian function shaped by collimator geometry. (2) slit-scattered protons, which undergo energy loss and trajectory changes due to collisions with the collimator. Its corresponding initial condition is characterized using Monte Carlo (MC) simulations and approximated by Gaussian and Lorentzian functions. Then the dose distributions in tissues were calculated by solving the proton transport equation. The depth dose profile was computed as a weighted sum of integral depth doses (IDDs) from individual monoenergetic components of the beam spectrum.
Results: The semi-analytic algorithm demonstrated excellent agreement with MC simulations for a collimator design featuring a ctc distance of 2.8 mm and slit width of 400 Ξm. The method accurately reproduced the peak-and-valley dose structure and allowed rapid calculations, highlighting its capability to handle various collimator configurations efficiently.
Conclusion: This study introduces a fast and robust semi-analytic algorithm for dose calculation in pMBRT, addressing key challenges related to lateral scattering and energy spectrum variability. The algorithm provides a practical and precise solution for treatment planning, supporting the clinical translation of pMBRT and enhancing its potential in proton radiotherapy.