Optimization of a Pelletron Accelerator for Radiobiologic Experiments Using Proton FLASH Radiation
Z Kaffey1*, S Rooks2, M Mccurdy3, J Eley4, (1) ,Vanderbilt University, Nashville, TN, (2) ,Philadelphia, PA, (3) Vanderbilt, ,,(4) Vanderbilt University School of Medicine, Nashville, TN
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PO-GePV-T-161 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: To establish an experimental platform for radiobiologic experiments using 4 MeV protons at variable dose rates.
Methods: We optimized a beam control and dosimetry system for an electrostatic Pelletron accelerator to enable radiobiologic experiments. We added a mechanical 1-mm-thick aluminum shutter into a new cross section of the beam line. With the shutter, the beam exposure time is remotely controlled with a precision of +/- 1 ms. A dedicated 0.030 mm thick aluminum exit window was also added to minimize beam energy loss and mitigate potential radiation degradation of polymer exit windows. We used a surface barrier detector (SBD) to measure fluence and the energy spectrum of the protons in vacuum and air. A Rutherford backscatter detector (RBD) was used as a primary beam monitor, providing minimal perturbation of the primary beam. This system relies on a gold foil with thickness of 120 nm and second SBD, off axis. To calculate dose and dose rate a Python-based tool was developed, using measured fluence values, shutter exposure times, and stopping power values from the National Institute of Standards and Technology. Radiochromic films were used to measure spatial distribution of the beam.
Results: For our sample exposure location, 5 cm from the exit window, the peak proton energy was 2.8 MeV, corresponding to a projected range in water of 133 microns. We established a control dose rate of 0.22 +/- 0.05 Gy/s, and by increasing the ion source hydrogen gas flow we established a FLASH dose rate of 124 +/- 21 Gy/s. Film measurements revealed a useable beam size of approximately 30 mm in diameter.
Conclusion: We developed a platform for radiobiologic experiments capable of proton FLASH exposures, suitable for cell culture monolayers or thin biologic samples.
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