Thermoacoustic range verification during pencil beam delivery of a clinical plan to an abdominal imaging phantom.
(2021) Radiotherapy & Oncology — Vol. 159, p. 224-230 (2021)
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- PURPOSE: The purpose of this phantom study is to demonstrate that thermoacoustic range verification could be performed clinically. Thermoacoustic emissions generated in an anatomical multimodality imaging phantom during delivery of a clinical plan are compared to simulated emissions to estimate range shifts compared to the treatment plan. METHODS: A single-field 12-layerproton pencil beam scanning (PBS)treatment plancreated in Pinnacle prescribing6 Gy/fractionwas delivered by a superconducting synchrocyclotron to a triple modality (CT, MRI, and US) abdominal imaging phantom.Data was acquired by four acoustic receivers rigidly affixed to a linear ultrasound array. Receivers 1-2 were located distal to the treatment volume, whereas 3-4 were lateral. Receivers' room coordinates were computed relative to the ultrasound image plane after co-registration to the planning CT volume. For each prescribed beamlet, a set of thermoacoustic emissions corresponding to varied beam energies were computed. Simulated emissions were compared to measured emissions to estimate shifts of the Bragg peak. RESULTS: Shifts were small for high-dose beamlets that stopped in soft tissue. Signals acquired by channels 1-2 yielded shifts of -0.2±0.7mm relative to Monte Carlo simulations for high dose spots (~40 cGy) in the second layer. Additionally, for beam energy ≥125 MeV, thermoacoustic emissions qualitatively tracked lateral motion of pristine beams in a layered gelatin phantom, and time shifts induced by changing phantom layers were self-consistent within nanoseconds. CONCLUSIONS: Acoustic receivers tuned to spectra of thermoacoustic emissions may enable range verification during proton therapy.
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Patch, S. K., Nguyen, C., Dominguez-Ramirez, D., Labarbe, R., Janssens, G., Cammarano, D., Lister, J., Finch, C., Lambert, J., Pandey, J., Bennett, C., Porteous, E., Chirvase, C., Cohilis, M., Souris, K., Ono, S., & Lynch, T. (2021). Thermoacoustic range verification during pencil beam delivery of a clinical plan to an abdominal imaging phantom. Radiotherapy & Oncology, 159, 224-230. https://doi.org/10.1016/j.radonc.2021.03.027 (Original work published 2021)