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  5. A Novel Source Tracking Method for Accurate and Comprehensive HDR Brachytherapy Quality Assurance Using Radiochromic Film Dosimetry

A Novel Source Tracking Method for Accurate and Comprehensive HDR Brachytherapy Quality Assurance Using Radiochromic Film Dosimetry

S Aldelaijan1,2,3,4*, P Papaconstadopoulos2,3 , H Bekerat3 , J Schneider2,3 , J Seuntjens2,5 , I Buzurovic6 , S Devic2,3 , (1) Department of Biomedical Engineering, Montreal Neurological Institute, Montreal, Canada, (2) Medical Physics Unit, McGill University, Montreal, Canada, (3) Department of Radiation Oncology, Jewish General Hospital, Montreal, Canada, (4) Biomedical Physics Department, King Faisal Specialist Hospital & Research Centre, Riyadh, Saudi Arabia, (5) Department of Oncology, McGill University, Montreal, Canada (6) Department of Radiation Oncology, Dana-Farber/Brigham & Women's Cancer Center, Harvard Medical School, Boston, USA

Presentations

(Wednesday, 8/1/2018) 7:30 AM - 9:30 AM

Room: Davidson Ballroom A

Purpose: To introduce a novel method for accurate and comprehensive quality assurance (QA) of high-dose-rate (HDR) brachytherapy based on radiochromic film dosimetry.

Methods: In order to reduce the positional uncertainty in the distance between a microSelectron V2 ¹�²Ir source and the measurement plane, a tracking method was developed based on the full-width at half-maximum (FWHM) of a dose profile along the source axis. Relative AAPM TG43 dose profiles at different depths (5 mm to 45 mm) were modeled and fitted. To verify the fit model, a single dwell position was delivered at the center of a 30 × 50 × 30 cm³ Solid Water™ phantom to a film at a nominal depth of 11 mm (five repeats). To verify the tracking method, eight films were irradiated simultaneously at different depths. For multiple positions, five dwell positions separated by 20 mm at variable times (60, 50, 40, 30 and 20 sec) were delivered to a film at 11 mm depth.

Results: It was shown that TG43 relative dose profiles could be modeled accurately using Pearson VII fits. A simple linear model [distance (mm) = 0.524 × FWHM (mm) - 0.322] can be used to predict the distance between the source and the measurement plane. Pearson VII peak decomposition analysis of the multi-position dose profile was shown to be effective to predict dwell positions (peak positions, within 0.5 mm) and times (peak amplitudes, within 0.5 sec).

Conclusion: A practical source tracking technique based on measurement of dose distribution FWHM was introduced. Dwell positions and times could be accurately deduced from a profile measurement using a peak decomposition analysis. We believe that these techniques have the potential to integrate afterloader QA, source QA, and first dwell position QA for a single channel (1D) or multiple channels (2D) HDR QA in a single measurement.

Funding Support, Disclosures, and Conflict of Interest: Supported in part by NSERC contract No. 386009. S.A. acknowledges scholarship support from King Faisal Specialist Hospital & Research Center (KFSH&RC). S.A. acknowledges partial support by the CREATE Medical Physics Research Training Network grant of the NSERC grant No. 432290. S.D. is a research scientist supported by FRSQ.

Keywords

HDR, Quality Assurance, Radiochromic Film

Taxonomy

TH- Brachytherapy: Calibration & Quality Assurance

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