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Feasibility of X-Ray Acoustic Computed Tomography as a Tool for Calibration and In Vivo Dosimetry of Radiotherapy Electron and Photon Beams

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S Hickling

S Hickling1*, M Hobson2 , I El Naqa1,2 , (1) McGill University, Montreal, Quebec (2) McGill University Health Centre, Montreal, Quebec

Presentations

MO-A-BRD-7 Monday 7:30AM - 9:30AM Room: Ballroom D

Purpose: This work simulates radiation-induced acoustic waves to assess the feasibility of x-ray acoustic computed tomography (XACT) as a dosimeter. XACT exploits the phenomenon that acoustic waves with amplitude proportional to the dose deposited are induced following a radiation pulse. After detecting these acoustic waves with an ultrasound transducer, an image of the dose distribution can be reconstructed in real-time.

Methods: Monte Carlo was used to simulate the dose distribution for monoenergetic 6 MeV photon and 9 MeV electron beams incident on a water tank. The dose distribution for a prostate patient planned with a photon 4-field box technique was calculated using clinical treatment planning software. All three dose distributions were converted into initial pressure distributions, and transportation of the induced acoustic waves was simulated using an open-source toolkit. Ideal transducers were placed around the circumference of the target to detect the acoustic waves, and a time reversal reconstruction algorithm was used to obtain an XACT image of the dose for each radiation pulse.

Results: For the photon water tank relative dosimetry case, it was found that the normalized acoustic signal amplitude agreed with the normalized dose at depths from 0 cm to 10 cm, with an average percent difference of 0.5%. For the reconstructed in-plane dose distribution of an electron water tank irradiation, all pixels passed a 3%-3 mm 2D gamma test. The reconstructed prostate dose distribution closely resembled the plan, with 89% of pixels passing a 3%-3 mm 2D gamma test. For all situations, the amplitude of the induced acoustic waves ranged from 0.01 Pa to 1 Pa.

Conclusion: Based on the amplitude of the radiation-induced acoustic waves and accuracy of the reconstructed dose distributions, XACT is a feasible technique for dosimetry in both calibration and in vivo environments for photon and electron beams and merits further investigation.

Funding Support, Disclosures, and Conflict of Interest: Funding from NSERC, CIHR and McGill University. SH acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the Natural Sciences and Engineering Research Council (Grant number: 432290)


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