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Feasibility of Combining Transmission Beams and Spread-Out Single-Energy Bragg Peaks for Proton FLASH Radiotherapy

C Ma, X Yang, R Liu, L Lin, D Bohannon, T Liu, J Bradley, J Zhou*, Department of Radiation Oncology and Winship Cancer Institute, Emory University, Atlanta, GA 30322

Presentations

TU-F115-IePD-F5-3 (Tuesday, 7/12/2022) 1:15 PM - 1:45 PM [Eastern Time (GMT-4)]

Exhibit Hall | Forum 5

Purpose: FLASH proton therapy using transmission beams (TBs) has limitations in OAR sparing. We investigated the feasibility of combining TBs and spread-out Bragg peaks (SOBPs) of single-energy proton beams (SESOBPs) using general pre-designed ridge filters (RFs) for FLASH treatment.

Methods: An in-house inverse planning tool was developed to optimize beam intensities with a combination of TBs and SESOBPs for FLASH planning. The SESOBPs were generated by shifting the BPs to the distal edge of the target using range shifters and then spreading out the BPs using general pre-designed bar RFs to obtain a uniform dose in the largest box within the target. The remaining target was treated with the TBs. To achieve FLASH dose rate for beam delivery, an iterative spot weighting optimization was conducted in the optimization process to push up the minimum MU/spot. A spherical target of 4.4 cm diameter in a water phantom was planned using the proposed method. 3D dose and dose rate distributions were evaluated.

Results: The minimum MU corresponding to a minimum delivered protons of 5×10^8 at a beam current of 165nA was achieved for a minimum spot delivery time of 0.5 ms. Having 95% of the target covered by the prescription dose, high homogeneity (D5%/D95%=1.07) and conformity (CI=1.10) were obtained. As expected, the SESOBP dose component was more weighted inside the target and the TB dose component was more weighted at the target boundary for dose compensation. The FLASH effect (>40Gy/s) was achieved in the whole target volume and the Body where received >10% of the prescription dose.

Conclusion: The preliminary results demonstrated that the combination of TBs and SESOBPs has the potential for FLASH RT with better sparing of the OARs. Further investigation will be needed before it is applied to clinical cases.

Keywords

Protons, Treatment Techniques, Radiation Therapy

Taxonomy

Not Applicable / None Entered.

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