Medical Physics Seminar - Liyong Lin PhD

A bundled IBO-IMPT framework provides degenerate solutions to simultaneously optimize contributions from dose, dose rate, and LET. The framework creates both spot maps for proton pencil beam scanning radiotherapy and CAD files to create patient-specific ridge filter assembly. The ridge filter assembly passively modulate energy of a transmission beam to allow conformal dose delivery. The rationale for using IBO-IMPT is that dose, dose rate, and LET are inextricably linked. For example, a higher LET can increase RBE up to 1.3 fold, whereas FLASH dose rates can reduce RBE (for normal tissue) by up to 50%. Thus, dose rate and LET may negate each other’s contribution unless each term is explicitly optimized. In addition, dose thresholds for FLASH were recently reported as 5-10 Gy, and these must be considered as part of the optimization. Biologists and physicians can use the IBO-IMPT output to investigate individual contributions of each term for preclinical studies and human clinical trials. Different optimization and GPU parallelization algorithms will be discussed as computationally efficient means to provide IBO-IMPT solution. A pixelated proton counting detector can be used to validate the IBO-IMPT solutions and ridge filter assembly design. The detector facilitates measurements of dose, instantaneous dose rate, and LET. Measurements can be further cross validated using a multi-layer strip ionization chamber (MLSIC) and Monte Carlo dose calculation. Validation of instant dose, dose rate and LET will be discussed for various solutions of patient-specific ridge filters, range compensators and proton spot maps provided by IBO-IMPT.