WE‐A‐108‐01: BEST IN PHYSICS (THERAPY) — A Real‐Time Applicator Position Monitoring System (RAPS) for Intracavitary High‐Dose‐Rate Brachytherapy

Abstract

Purpose: To develop a real‐time applicator position monitoring system (RAPS) for intracavitary brachytherapy using an infrared camera and reflective markers. Methods: 3D imaging‐guided brachytherapy requires high accuracy of applicator localization; however, applicator displacement can happen during patient transfer for imaging and treatment delivery. No continuous applicator position monitoring system is currently available. The RAPS system was developed for continuous applicator position monitoring without additional radiation dose to patients. The RAPS system includes an infrared camera, reflective markers, an infrared illuminator, and image processing software. After reflective markers are firmly attached to the applicator and patient body, applicator displacement are measured by computing the relative change in distance between the markers. The reflective markers are magnetic resonance imaging (MRI) compatible, suitable for MRI‐guided conformal HDR brachytherapy paradigm. In our prototype, a Microsoft Kinect sensor with a resolution of 640 by 480 was used as an infrared camera. A phantom study was carried out to compare RAPS' measurements with known displacements ranging from −15 mm to +15mm. A reproducibility test was also conducted. Results: The RAPS can achieve 4 frames per second using a laptop with Intel Core 2 dual CPU. When the pixel size was 0.95 mm, the difference between RAPS' measurements and known shifts ranged from 0 to 0.8 mm, with the mean value of 0.1 mm and a standard deviation of 0.44 mm. The system reproducibility was within 0.6 mm after 10 reposition trials. At SAD of 60 cm, 7 cm camera position uncertainty in vertical direction introduced 1.0 mm measurement uncertainty. Conclusion: This work demonstrates the feasibility of a real‐time infrared camera based brachytherapy applicator monitoring system. Less than 1mm accuracy was achieved when using an off‐the‐shelf low resolution infrared camera.