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Use of 2D Robotic Scanning to Simulate Proton PBS at FLASH Dose Rates

E Diffenderfer*, M Kim, J Zou, B Teo, S Avery, D Carlson, C Koumenis, J Metz, K Cengel, L Dong, R Wiersma, University of Pennsylvania, Philadelphia, PA


(Monday, 7/13/2020) 3:30 PM - 5:30 PM [Eastern Time (GMT-4)]

Room: Track 3

Purpose: Ultra-high dose rate (FLASH) proton radiation has demonstrated increased normal tissue sparing in small animal pre-clinical experiments when compared to clinically standard proton dose rates. Translation to pencil beam scanning (PBS) in the clinic requires understanding the consequences of spatio-temporal variations on the FLASH effect. To investigate in a small animal pre-clinical setting, we introduce a novel 2D robotic platform to simulate the spatial and temporal aspects of PBS thereby opening up new avenues of FLASH research with the goal of bridging the gap to the clinic.
Methods: We developed a control system for the fixed proton research beam line which allows precise beam intensity and time structure modulation. Beam delivery time structure is recorded using a NaI prompt gamma detector. The proton beam was collimated by a 5x5 mm square collimator. An X-Y translational stage was utilized to move the target in synchrony with the beam intensity modulation and recreate spatio-temporal variations with characteristics similar to PBS.
Results: We have shown that PBS FLASH delivery can be simulated on a fixed proton beam line using beam intensity modulation and a 2D robotic stage for target positioning. System capabilities were demonstrated by delivery of a large uniform proton field with arbitrary shape defined by the summation of individually collimated proton spots. Dose rate of the collimated spots was ~100 Gy/s and above the threshold for FLASH effects.
Conclusion: Irradiation techniques and instrumentation were developed to investigate the spatio-temporal effects of FLASH PBS with a 2D robotic stage scanning system for small animal irradiation, which enables investigation of intensity modulation in the setting of FLASH proton radiation. As spatio-temporal effects may be vital to the successful translation of FLASH radiotherapy to the clinic, future work will include experimental studies using the robotic PBS system to deliver FLASH to mouse models.


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