SRS Multiple Brain Metastasis in Palliative Patients as Potential Indication Site for Multi-Energy Conformal FLASH Using a Proton Linac
A Kolano1,2, W Kozlowska1*, T Gray3, C Liu3, P Xia3, J Farr1,2, (1) Applications Of Detectors And Accelerators To Medicine (ADAM) SA, Meyrin, Switzerland,(2) Advanced Oncotherapy plc, London, UK (3) The Cleveland Clinic Foundation, Cleveland, OH
Presentations
SU-H400-IePD-F4-4 (Sunday, 7/10/2022) 4:00 PM - 4:30 PM [Eastern Time (GMT-4)]
Exhibit Hall | Forum 4
Purpose: To investigate proton linac use for delivering Stereotactic Radiosurgery (SRS) conformal FLASH to patients with multiple brain metastasis, as an alternative to photon treatments.
Methods: Current systems can deliver ultra-high dose rates (UHDRs) only at the highest energy, where single energy layer Bragg peaks lie outside of the patient. Proton linacs, however, have intensity invariant on energy which, combined with a fast spot and energy switching time of 5 ms, allows for multi-energy FLASH irradiation of targets within 0.5 s. Brain metastasis treatment plans were created using a commercial treatment planning system, with beam parameters of a commercial proton linac. The FLASH-optimized plans were compared to Volumetric-modulated Arc Therapy (VMAT) SRS plans in terms of the target coverage, dose to Organs at Risk (OARs), and Dose-Rate average (DRₐᵥ). Robustness of 2 mm isotropic position-, and 2% density-uncertainty was used to plan all FLASH cases. Each target was treated with a dedicated single field.
Results: Evaluated FLASH dose rates up to 100 Gy/s were achieved, with a trade-off between conformity and low dose in normal tissue. FLASH-plan spot count was minimized to achieve UHDRs. Flash-plan quality is comparable to nominal photon plans, with lower OARs dose. Proton-FLASH conformal planning reduced average brain dose by over 1 Gy; and to 0 for other OARs. Local increase in brain dose at D1/2 level was observed with UHDRs, though benefits from effective dose reduction due to FLASH Effect (FE) are expected.
Conclusion: It is possible to plan clinically relevant conformal FLASH plans for SRS brain metastasis using a proton linac. In studied cases, the UHDR averaged over all brain targets was 58 Gy/s. Target conformity is comparable to photon plans, with lower OARs dose, indicating that brain metastasis are potential candidates for FLASH therapy using a linac, with additional benefit of the FE.
Funding Support, Disclosures, and Conflict of Interest: Jonathan Farr holds a senior management position at ADAM SA, Meyrin, Switzerland and is a shareholder in Advanced Oncotherapy (AVO), plc, London, UK. Anna-Maria Kolano is an employee of ADAM SA and participates in the employee share option program of AVO. Ping Xia receives research funding support from AVO.
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