arXiv subjects

Nathan Harrison

Publications and source records attributed to Nathan Harrison.

2 recordsLinked to original sources

arXiv2023

A novel inverse algorithm to solve IPO-IMPT of proton FLASH therapy with sparse filters

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.

physics.med-ph↗

arXiv2022

Validation of the Quantum Physics Processes Underlying the Integrated Optimization of Proton FLASH Radiotherapy

FLASH is a new treatment modality that requires optimization of dose, dose rate, and LET. Here we validate these three quantities under FLASH conditions, which includes the quantum uncertainty in the time-dependent instantaneous dose rate (IDR) curves and LET spectra that underlie the newly proposed integrated optimization framework. Measurements of dose, IDR, and LET were performed at the Emory Proton Therapy Center using a FLASH proton beam with a nominal energy of 250 MeV and a 3D printed ridge filter. Because 3D printing resin is made from a proprietary chemical formula, we developed a method for realistically characterizing and modeling the material in simulations. Absolute dose in 3D space was measured using a 2D MatriXX PT detector as well as by a novel 4D multi-layer strip ionization chamber (MLSIC), which also simultaneously measures IDR. Further timing data was measured in the secondary beam by detecting prompt gammas using a Minipix Timepix3; a second detector, Advapix Timepix3, was used to measure LET. To account for the quantum mechanical nature of particle transport, we developed a technique for detecting individual protons within a high flux primary beam, which was necessary for properly measuring LET spectra. TOPAS simulations agreed with measurement, with absolute dose typically having a gamma passing rate of at least 95% (3 mm/3% criteria). Likewise, IDR and LET showed good agreement, with averaged IDR values agreeing within 0.3% with fluctuations on the order of 10%, and LET distributions overlapping by at least 85% and showing an increase in high LET components (greater than 4 keV/um) with increasing depth. As LET and FLASH optimization continues to grow in popularity, measuring IDR, LET, and dose will become even more important, and we expect that the methods described here will prove to be useful tools in radiotherapy treatment planning and QA.

physics.med-ph↗