A novel inverse algorithm to solve IPO-IMPT of proton FLASH therapy with sparse filters
Nathan Harrison, Minglei Kang, Ruirui Liu, Serdar Charyyev, Niklas Wahl, Wei Liu, Jun Zhou, Kristin A. Higgins, Charles Simone, Jeffrey Bradley, William S. Dynan, Liyong Lin
Purpose:The recently proposed IPO-IMPT framework allows simultaneous optimization of dose, dose rate, and LET for FLASH treatment planning. Finding solutions to IPO-IMPT is difficult due to computational intensiveness. Nevertheless, an inverse solution that simultaneously specifies the geometry of a sparse filter and weights of a proton intensity map is desirable for both clinical and preclinical applications. Such solutions can reduce effective biological dose to organs at risk in cancer patients as well as reduce the number of animal irradiations needed to derive extra biological dose models in preclinical studies.
Methods:Unlike our initial forward heuristic, this inverse IPO-IMPT solution includes simultaneous optimization of sparse range compensation, sparse range modulation, and spot intensity. The daunting computational tasks vital to this endeavor were resolved iteratively with a distributed computing framework to enable Simultaneous Intensity and Energy Modulation and Compensation (SIEMAC). SIEMAC was demonstrated on a human lung cancer patient and a minipig.
Results:SIEMAC improves maps of spot intensities and patient-field-specific sparse range compensators and range modulators. For the lung cancer patient, at our max nozzle current of 300 nA, dose rate coverage above 100 Gy/s increased from 57% to 96% in the lung and from 93% to 100% in the heart, and LET coverage above 4 keV/um dropped from 68% to 9% in the lung and from 26% to <1% in the heart. For a simple minipig plan, the FWHM of the dose, dose rate, and LET distributions decreased by 30%, 1.6%, and 57%, respectively, again with similar target dose coverage, thus reducing uncertainty in these quantities for preclinical studies.
Conclusion:The inverse solution to IPO-IMPT demonstrated the capability to simultaneously modulate sub-spot proton energy and intensity distributions for clinical and preclinical studies.
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Department of Radiation and Cellular Oncology University of Chicago（辐射与细胞肿瘤学系，芝加哥大学）；Division of Environmental and Occupational Health Sciences University of Illinois at Chicago（环境与职业卫生科学系，伊利诺伊大学芝加哥分校）；Department of Radiation Oncology and Winship Cancer Institute Emory University（放射肿瘤学系和Winship癌症研究所，埃默里大学）
