An ultra-high dose rate Bragg peak tracking technique provides more affordable proton radiotherapy for cancer patients: From principle to experimental validation.

Abstract

Purpose: This work aims to experimentally validate a novel cost-effective solution for achieving both conventional dose-rate and ultra-high dose rate (UHDR) deliveries in pencil beam scanning proton therapy.

Methods: A proton therapy delivery solution was previously developed by our group using only a single pristine Bragg peak of the highest energy proton beams from a cyclotron. This approach streamlines upstream beam modifiers, including energy degrader, selection and focusing systems, while utilizing of universal range shifters (URS) and range compensators (RCs) to preserve high beam transmission efficiency for UHDR beam delivery. It achieves the Bragg peak tracking and target dose conformity, making it potentially suitable for FLASH radiation therapy. In the current study, we highlighted the realization of the solution by using URS and customized beam-specific RCs via simulation in an in-house treatment planning software (TPS) which is then fabricated by a 3D printer, facilitating precise beam shaping and Bragg peak tracking. Experimental validation of this method was conducted using a clinical proton system to showcase a practical solution that can be translated into realistic operation. Both dose and dose rate were measured and compared to treatment planning results.

Results: The proton convolution superposition (PCS) dose calculation was benchmarked by the Monte Carlo calculation. Matrixx PT measured the delivered dose in the uniform and head-neck (HN) phantom, and the gamma passing rates were > 99 % in the water phantom. The gamma rate was > 98 % for the HN phantom for this distal tracking method. The measured dose difference between the TPS and HN phantom was < 2 %. The implementation of a high temporal resolution strip ion chamber detector array enabled accurate measurement of the spot time structure, facilitating 3D dose rate reconstruction across various beam currents.

Conclusion: The experimental validation successfully demonstrated the dosimetric accuracy and robustness of this proposed delivery method. The employment of the Bragg peak tracking method holds great promise for reducing treatment delivery costs for future UHDR and conventional dose rate proton radiation therapy, ultimately benefiting a larger population of patients.