Compact Radiation Detector for Wireless Thermoacoustic Range Verification Detects Pulse-To-Pulse Variations During Conventional Proton Therapy
S Patch1*, Y Hao2, T Zhao2, S Pauly3, (1) Acoustic Range Estimates, Chicago, IL, (2) Washington University School of Medicine, St. Louis, MO, (3) Rapiscan | AS-E, Oak Ridge, TN
Presentations
PO-GePV-T-147 (Sunday, 7/10/2022) [Eastern Time (GMT-4)]
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Purpose: Theoretical analysis of thermoacoustic signals requires knowing the time at which protons hit the target. However, synchrocyclotrons deliver O(1 pC) over several microseconds during conventional proton therapy. Resulting thermoacoustic emissions are weak and bandlimited by the beam current, I(t). A clinical thermoacoustic device should include a compact radiation detector that can measure I(t). We compared a compact radiation detector to a PMT assembly with a fast plastic scintillator with O(10 ns) decay time.
Methods: A large (0.5 m long) PMT assembly with plastic scintillator requiring -2 kV power supply used for early prototype measurements was compared to a compact (3x3x2 cm3), battery powered radiation detector with “glass” scintillator. Current from the scintillator was converted to a voltage by a 50 Ohm resistor (V=IR), then inverted and de-amplified by a factor of 5. Signals from both detectors were sampled at 500 MSPS.
Results: Both detectors are susceptible to saturation. Preferred positioning of the compact detector, mounted onboard a thermoacoustic device resulted in severe saturation (Fig. 1). The PMT assembly has a faster response time than the compact detector, but signal is noisier from the PMT assembly. Pulse-to-pulse variations are obscured by noise in the PMT assembly signals but are obvious to the naked eye in compact detector signals.
Conclusion: The compact detector has rapid rise time and can already serve as a trigger for thermoacoustic signal acquisition. Tuning is required to avoid saturation and minimize decay time to accurately reflect beam current, I(t), during conventional delivery. More work is required to monitor beam current during ultra-high dose rate FLASH therapy. The compact detector reveals pulse-to-pulse variability. Thermoacoustic signals are often averaged to reduce noise, but care should be taken to weight pulses appropriately.
Funding Support, Disclosures, and Conflict of Interest: Dr. Patch was funded in part by NIH SBIR award #R43CA243764. Drs. Zhao and Hao funded by Washington University department of Radiation Oncology, which also provided beam time.
Keywords
Protons, Quality Assurance, Radiation Detectors
Taxonomy
TH- External Beam- Particle/high LET therapy: Proton therapy – quality assurance
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