Performance and Clinical Trial in vivo of a Scintillation Dosimeter in Brachytherapy

Abstract

A clinical trial of a new scintillation dosimeter confirms its usefulness for in vivo dosimetry during prostate HDR brachytherapy treatment. The dosimeter consists of a plastic scintillator coupled to an optical fibre with a radio-opaque platinum marker placed at the tip. The combination of tissue equivalence, real time readout and small size makes this dosimeter uniquely suited for in vivo verification of patient treatments. The angular dependence of the dosimeter is important and was determined both theoretically using Monte Carlo simulation and experimentally using a phantom with an HDR ¹⁹²Ir source. We found that the radio-opaque marker did not compromise the angular response of the dosimeter. A realistic test of the effects of the radio-opaque marker for brachytherapy was obtained from simulation and experiment with the source travelling along a line at a fixed distance from the scintillator axis and parallel to it. Fifteen prostate HDR brachytherapy patients were recruited to the clinical trial. The treatment volume and the position of the dosimeter could be accurately determined in the patient frame of reference by viewing the images of gold prostate markers and the platinum marker in the radiograph. For all but one patient the dose received by the urethra was within 1.5 Gy of the dose calculated by the planning system.