RECTAL THERMOLUMINESCENT DOSIMETER MEASUREMENTS USING THE MICROSELECTRON HIGH-DOSE-RATE AFTERLOADER IN POSTOPERATIVE INTRAVAGINAL RADIATIONCASES

Purpose: The purpose of this study is twofold: First, to measure the d ose 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 i n 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 R ate system. The method of measurement employed flexible vinyl rectal p robes (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 c overing a rectal length from one to two centimeters. The peak doses fo r the anterior rectal wall ranged from 60% to 110% of prescribed dose. In-phantom measurements used layers of phantom material that containe d a special source tube for the Iridium-192 source as well as Thermolu minescent Dosimeter tube(s) positioned at 1 cm distance from the sourc e tube. The afterloader was programmed to deliver 300 cGy at 1 cm alon g its treatment length. Conclusion: The Thermo Luminescent Dosimeters measurements showed good agreement with the doses expected on the basi s of the treatment plan.