Simultaneous Dose and Dose Rate Optimization with Transmission Beams and Bragg Peaks for Proton FLASH Therapy
Y Lin1*, B Lin1,2, S Fu2, M Folkerts3, E Abel3, J Bradley1, H Gao1, (1) Winship Cancer Institute of Emory University, Atlanta, GA, (2) Shandong University, Jinan, Shandong, China, (3) Varian Medical Systems, Palo Alto, CA
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SU-IePD-TRACK 5-1 (Sunday, 7/25/2021) 5:30 PM - 6:00 PM [Eastern Time (GMT-4)]
Purpose: With the radiation at ultra-high dose rates, the FLASH therapy (FLASH-RT) can substantially reduce normal tissue toxicities while maintaining tumor response. By far the only commercially available devices that can deliver ultra-high dose rates required for general-purpose clinical FLASH-RT are isochronous cyclotron based proton systems, for which high-energy transmission beams (TB) are needed to achieve ultra-high dose rates for deep-seated tumor targets. However, planning with TB alone does not fully leverage the degrees of freedom for dose shaping as traditional intensity modulated proton therapy (IMPT) via the Bragg peaks (BP) of multi-energy proton beams at the tumor targets. This work aims to develop a simultaneous dose and dose rate optimization (SDDRO) method with the joint use of TB and BP, namely SDDRO-Joint.
Methods: Different from IMPT that only optimizes the dose distribution, SDDRO enables the dose rate optimization for the purpose of FLASH-RT, in addition to the dose optimization. During SDDRO-Joint, while TB primarily cover the tumor boundary in order to achieve ultra-high dose rate coverage of organs-at-risk (OAR) surrounding tumor targets, BP are placed inside tumor targets to further improve the target dose conformality and sparse the normal-tissue dose, i.e., the FLASH sparing by TB and the dose sparing by BP.
Results: SDDRO-Joint (both TB and BP) was validated in comparison with IMPT-BP (BP only), IMPT-TB (TB only), and SDDRO-TB (TB only). IMPT-BP serves as the gold standard for the dose distribution. SDDRO-TB serves as the gold standard for the dose rate distribution. The results suggest that SDDRO-Joint substantially increased the target dose conformality from SDDRO-TB, while preserving the dose rate coverage. Noticeably SDDRO-Joint had the best conformal index values, e.g., higher than IMPT-BP as well.
Conclusion: A new treatment planning method SDDRO-Joint is developed to simultaneously optimize dose and dose rate distribution for FLASH-RT.
Funding Support, Disclosures, and Conflict of Interest: This research is supported in part by Varian Medical Systems and NIH grant R01CA250921.
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