Program Information
Experimental Sensitivity Analysis of X-Ray Acoustic Computed Tomography for Radiotherapy Dosimetry Applications
S Hickling1*, M Hobson2 , I El Naqa3 , (1) McGill University, Montreal, QC, (2) McGill University Health Center, Montreal, QC, (3) University of Michigan, Ann Arbor, MI
Presentations
WE-RAM1-GePD-TT-2 (Wednesday, August 2, 2017) 9:30 AM - 10:00 AM Room: Therapy ePoster Theater
Purpose: X-ray acoustic computed tomography (XACT) is an emerging dosimetry technique that detects radiation-induced acoustic waves to form images of the dose deposited in an irradiated medium. This work explores the ability of XACT to detect changes in field size, field location, and source to surface distance (SSD).
Methods: An immersion ultrasound transducer was placed inside a water tank to detect the acoustic waves induced following irradiation by a 10 MV flattening filter free beam. By rotating the collimator, transducer signals were obtained every 6° around the field. A filtered back projection algorithm was used to reconstruct an image of the relative dose distribution. Nominally, the water tank was placed at an SSD of 90 cm and the field size was set to 4 cm x 4 cm at the detector depth of 10 cm. XACT images were acquired and analyzed for incremental changes in field size, field location, and SSD.
Results: Profiles extracted from XACT images were sensitive to collimator field size changes of 2 mm, with XACT and film measured field sizes agreeing within experimental uncertainty. When the field center was shifted 2 mm, the center of the field as determined from the XACT image was found to shift by 1.9 ± 0.2 mm. An XACT image acquired at an SSD of 92 cm had a decrease in relative image intensity of 10 ± 5% compared to an XACT image at an SSD of 90 cm. This is close to the expected change in intensity of 4%, as determined by the inverse square law.
Conclusion: XACT is sensitive to field size changes and field shifts of 2 mm, and relative dose changes on the order of 4%. This makes XACT a promising dosimetry technique for a variety of applications, including relative water tank and in vivo dosimetry.
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 award. This work is partly supported by the Canadian Institutes of Health Research (CIHR) grants MOP-114910 and MOP- 136774
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