Purpose: To investigate feasibility of ionacoustic detection as an in vivo method for measuring proton dose depositions during patient treatments. Ionacoustic detection proposes an efficient and low-cost solution to monitoring range uncertainty in patient plan delivery due to patient setup, imaging, beam delivery, and dose calculations. With pencil beam scanning being the most prevalent method of proton dose delivery now, single pulse acquisition is crucial in implementing this method of detection in the clinic.
Methods: Proton induced acoustic range measurements were performed with a proton synchrocyclotron (Mevion S250i Hyperscan) at energies ranging from 45.5MeV to 227.15MeV. A low-frequency 0.5MHz transducer was placed in a water tank along the beam axis and then connected to a two-stage amplification system placed in a borated-polyethylene shielding box, giving signal a total 100dB amplification. The signal was then connected to a dispatch board and sent outside the treatment room to be viewed on a digital oscilloscope. With the smallest single deposition of charge in patient treatments being 4pC, datasets were gathered with no signal averaging and a charge-per-pulse of 7pC/pulse. Proton induced acoustic dosimetric measurements were performed in the same manner, with charge depositions ranging from 0.25pC to 7pC being delivered at an energy of 201.14MeV.
Results: With spots delivered with 7pC/pulse, variations in range for single pulse signal acquisitions were measured to be within 1mm of the mean for all energies, with a systematic shift of approximately 2mm. The largest standard error was calculated to be 0.7mm. Dosimetric results with a linear trend allow a relative means of assessment for relating the charge deposited in the medium to the deposited dose.
Conclusion: With single pulse acquisitions having sub-millimeter range variations, ionacoustic detection is proven to be viable in vivo method for measuring proton dose depositions with high precision during patient treatments.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Institute of Health (R37CA240806), American Cancer Society (133697-RSG-19-110-01-CCE), and The Oklahoma Center for Advancement of Science and Technology (OCAST HR19-131).
Protons, Treatment Verification, Photoacoustics
TH- External Beam- Particle/high LET therapy: Range verification (in vivo/phantom): photoacoustic/optical