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

Abstract

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.

Analysis and Adjustment of Positioning Error of PSD System for Mobile SOF-FTIR

“…Fortunately, the position sensitive detector (PSD) provides us with another method of spot location detection. PSD is an analogue optical sensor which consists of a special monolithic PIN photodiode with several electrodes in order to achieve detection in one or two dimensional position detection [8]. The output of the PSD is a function of the center of gravity of the total light quantity distribution on the active area.…”