A high spatial and temporal resolutions quality assurance tool for checking the accuracy of HDR source dwell positions and times

Abstract

In High Dose Rate (HDR) brachytherapy, treatment dose to patients is highly dependent on the accuracy of positioning and duration of the source. Source misplacement or wrong duration of treatment could potentially result in adverse clinical side effects to patients. In order to maintain successful treatment for patients, an independent Quality Assurance (QA) verification is crucial to measure the High Dose Rate (HDR) source positioning and dwell time periodically to ensure the prescribed dose is correct and safe for brachytherapy treatment.

The current QA practice used to validate the accuracy of dwell time of the source is by using a stopwatch and measure the dwell position on the source position check ruler. Nevertheless, reaction time of human poses a major concern regarding the accuracy in these manual operating procedures.

In this thesis, a new QA tool is proposed to acquire accurate information about time structure and source positioning in HDR brachytherapy. The tool consists of a consumer-grade webcam, a source position check ruler, a laptop computer and a custom-made combined camera-ruler mounting tool. The camera is used to capture the motion of the moving source in real time. Each frame contains positional and temporal information that are important to determine the difference between the measured and the actual HDR source position and time structure. Finally, a Graphical User Interface (GUI) application program is developed to receive the input from the camera for image processing. The measured results (time structure and positional information) are displayed on the computer screen as the output of the designed application.

The tool was found to be able to reduce the time required significantly for the QA and minimize the impact of human errors. At the time of writing, the sensitivity of the system to luminous changes in the environment warrants further efforts to render the tool even more useful.

Based on the experimental results, the accuracy of dwell time measured by the proposed system was ± 40 ms. The minimum detectable dwell time of the proposed system was 200 ms. The range of effective dwell position that could be measured by the system ranged from 1300 mm to 1500 mm (excluding 1300 mm and 1500 mm). The accuracy of dwell position measured by the proposed system was ± 1mm.