Program Information
In Vivo Detection of Radiation-Induced Acoustic Waves for Treatment Delivery Verification: A Simulation Study
S Hickling1*, M Hobson2 , M Renaud3 , I El Naqa4 , (1) McGill University, Montreal, QC, (2) McGill University Health Center, Montreal, QC, (3) McGill University, Montreal, QC, (4) University of Michigan, Ann Arbor, MI
Presentations
SU-F-708-1 (Sunday, July 30, 2017) 2:05 PM - 3:00 PM Room: 708
Purpose: Acoustic waves with properties related to deposited radiation dose are induced in patients via the photoacoustic effect following a pulse of linac irradiation. Through simulations, this work investigates how using a single ultrasound transducer to detect these induced acoustic waves can yield useful information to verify accurate treatment delivery.
Methods: The CT scan and dose plan for a prostate patient treated with volumetric modulated arc therapy were obtained, and the dose distribution following a single pulse of irradiation at a given control point was calculated using Monte Carlo simulations. The dose distribution was empirically converted into an induced pressure distribution, and the propagation of acoustic waves was modelled to obtain the time-varying pressure signal at a simulated transducer location. The transducer was positioned at the perineum, since this setup has been shown to be an effective location for intrafraction motion monitoring. The signal was filtered to account for bandwidth limitations of a realistic transducer.
Results: By mapping the simulated time-varying transducer signal into distance using a constant speed of sound and propagating it along the detection line, it was observed that peaks in the acoustic signal coincide with gradients in the dose distribution. A 3 mm set up error was introduced, which resulted in a detectable 2.1 μs transducer signal shift. Since this technique measures the acoustic waves induced following a single pulse of irradiation, the transducer signal at different control points varied widely as the dose deposited by a given pulse changed.
Conclusion: This work demonstrates that detecting radiation induced acoustic waves at a clinically feasible transducer location during radiotherapy provides information regarding the real-time properties of the dose distribution. Combining this technique with intrafraction ultrasound imaging would be useful to overlay the inferred information about the dose distribution from the acoustic signal onto an anatomical ultrasound image.
Funding Support, Disclosures, and Conflict of Interest: S. H. acknowledges support by the NSERC CREATE Medical Physics Research Training Network grant 432290 and an NSERC PGSD3 scholarship. This work is partly supported by the Canadian Institutes of Health Research (CIHR) grants MOP-114910 and MOP- 136774.
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