Localization of high dose rate 192Ir source during brachytherapy treatment using silicon detectors

Abstract

A system for in vivo tracking of 192Ir source during high dose rate (HDR) brachytherapy treatments has been built using silicon pad detectors as image sensors and knifeedge lead pinholes as collimators. HDR brachytherapy utilizes moving a small (2-4 mm long) radioactive (usually 192Ir) source within body cavity or tumor to deliver fractionated therapy dose to designated volume. The source is pulled and pushed within catheters (needles or applicators) which are operatively inserted into the target volume before the treatment. Positions and dwell times of the source in catheters are calculated by treatment planning programs. Various kind of errors and inaccuracies, such as displacements of catheters between treatment steps, can and do occur and often remain undetected since procedure only rely on a computer controlled mechanical delivery system (afterloader). An independent system for verifying of HDR treatment would therefore be desirable. With self-images obtained from a dual-pinhole system the source location can be reconstructed in three dimensions. Due to high speed of silicon detector readout system the source position can be determined in real time allowing on-line detection of deviations from planned treatment. The performance of the system was tested with 1 Ci 192Ir clinical source in air and plexi-glass phantom. The movements of the source could be tracked in a field of view of approximately 20 × 20 × 20 cm3 with absolute precision of about 10 millimeters and relative position of around 1.5 millimeter.