WE-DE-201-07: Measurement of Real-Time Dose for Tandem and Ovoid Brachytherapy Procedures Using a High Precision Optical Fiber Radiation Detector

• Published in: Medical physics (Lancaster) Vol. 43; no. 6; pp. 3809 - 3810
• Main Authors: Belley, MD, Faught, A, Moore, B, Subashi, E, Langloss, B, Therien, MJ, Yoshizumi, TT, Chino, JP, Craciunescu, O
• Format: Journal Article
• Language: English
• Published: United States American Association of Physicists in Medicine 01-06-2016
• Subjects: 60 APPLIED LIFE SCIENCES; BRACHYTHERAPY; Computed tomography; COMPUTERIZED TOMOGRAPHY; DOSE RATES; Dosimetry; Image sensors; IRIDIUM 192; Optical fiber testing; OPTICAL FIBERS; Optical sensors; QUALITY ASSURANCE; QUALITY MANAGEMENT; RADIATION DETECTORS; RADIATION PROTECTION AND DOSIMETRY; Real time information delivery; Scintillation detectors; TIME DEPENDENCE
• ISSN: 0094-2405; 2473-4209
• DOI: 10.1118/1.4957812

Purpose:
Development of a novel on-line dosimetry tool is needed to move toward patient-specific quality assurance measurements for Ir-192 HDR brachytherapy to verify accurate dose delivery to the intended location. This work describes the development and use of a nano-crystalline yttrium oxide inorganic scintillator based optical-fiber detector capable of acquiring real-time high-precision dose measurements during tandem and ovoid (T&O) gynecological (GYN) applicator Ir-192 HDR brachytherapy procedures.
Methods:
An optical-fiber detector was calibrated by acquiring light output measurements in liquid water at 3, 5, 7, and 9cm radial source-detector-distances from an Ir-192 HDR source. A regression model was fit to the data to describe the relative light output per unit dose (TG-43 derived) as a function of source-detector-distance. Next, the optical-fiber detector was attached to a vaginal balloon fixed to a Varian Fletcher-Suit-Delclos-style applicator (to mimic clinical setup), and localized by acquiring high-resolution computed tomography (CT) images. To compare the physical point dose to the TPS calculated values (TG-43 and Acuros-BV), a phantom measurement was performed, by submerging the T&O applicator in a liquid water bath and delivering a treatment template representative of a clinical T&O procedure. The fiber detector collected scintillation signal as a function of time, and the calibration data was applied to calculate both real-time dose rate, and cumulative dose.
Results:
Fiber cumulative dose values were 100.0cGy, 94.3cGy, and 348.9cGy from the tandem, left ovoid, and right ovoid dwells, respectively (total of 443.2cGy). A plot of real time dose rate during the treatment was also acquired. The TPS values at the fiber location were 458.4cGy using TG-43, and 437.6cGy using Acuros-BV calculated as Dm,m (per TG-186).
Conclusion:
The fiber measured dose value agreement was 3% vs TG-43 and −1% vs Acuros-BV. This fiber detector opens up new possibilities for performing patient-specific quality assurance for Ir-192 HDR GYN procedures.
Funding from Coulter Foundation, Duke Bio-medical Engineering. Company is being created around the detector technology. Duke holds patents on the technology.