Usefulness of direct‐conversion flat‐panel detector system as a quality assurance tool for high‐dose‐rate 192Ir source

摘要

The routine quality assurance (QA) procedure for a high-dose-rate (HDR) 192 Ir radioactive source is an important task to provide appropriate brachytherapy. Traditionally, it has been difficult to obtain good quality images using the 192 Ir source due to irradiation from the high-energy gamma rays. However, a direct-conversion flat-panel detector (d-FPD) has made it possible to confirm the localization and configuration of the 192 Ir source. The purpose of the present study was to evaluate positional and temporal accuracy of the 192 Ir source using a d-FPD system, and the usefulness of d-FPD as a QA tool. As a weekly verification of source positional accuracy test, we obtained 192 Ir core imaging by single-shot radiography for three different positions (1300/1400/1500 mm) of a check ruler. To acquire images for measurement of the 192 Ir source movement distance with varying interval steps (2.5/5.0/10.0 mm) and temporal accuracy, we used the high-speed image acquisition technique and digital subtraction. For accuracy of the 192 Ir source dwell time, sequential images were obtained using various dwell times ranging from 0.5 to 30.0 sec, and the acquired number of image frames was assessed. Analysis of the data was performed using the measurement analysis function of the d-FPD system. Although there were slight weekly variations in source positional accuracy, the measured positional errors were less than 1.0 mm. For source temporal accuracy, the temporal errors were less than 1.0%, and the correlation between acquired frames and programmed time showed excellent linearity ( R 2 = 1 ). All 192 Ir core images were acquired clearly without image halation, and the data were obtained quantitatively. All data were successfully stored in the picture archiving and communication system (PACS) for time-series analysis. The d-FPD is considered useful as the QA tool for the 192 Ir source.PACS number: 87.56.Fc