Rectal thermoluminescent dosimeter measurements using the microselectron high dose rate afterloader in postoperative intravaginal radiation cases

Abstract

Purpose : The purpose of this study is twofold: First, to measure the dose distribution along the anterior and posterior rectal wall, compare them to the prescribed dose and establish the rectal length receiving the maximum dose. Second, to carry out in-phantom dose measurements in order to confirm that the dose planned is in fact the dose delivered. Methods and Materials : The dose distribution along the anterior and posterior rectal wall was measured for a group of 25 Gynecologic cases treated with a vaginal cylinder, using the MicroSelectron High Dose Rate system. The method of measurement employed flexible vinyl rectal probes (1 or 2 cm diameter). Two fine plastic tubes, each containing 15 Thermo Luminescent Dosimeters rods, were attached along the probe on opposite sides to measure the anterior and posterior rectal wall dose distributions. Results : The dose distribution exhibited a sharp peak covering a rectal length from one to two centimeters. The peak doses for the anterior rectal wall ranged from 60% to 110% of prescribed dose. In-phantom measurements used layers of phantom material that contained a special source tube for the Iridium-192 source as well as Thermoluminescent Dosimeter tube(s) positioned at 1 cm distance from the source tube. The afterloader was programmed to deliver 300 cGy at 1 cm along its treatment length. Conclusion : The Thermo Luminescent Dosimeters measurements showed good agreement with the doses expected on the basis of the treatment plan.