In vivo Measurement of Bladder and Rectum Doses of High-Dose-Rate Brachytherapy in Gynaecologic Tumors and Their Comparison with the Computer Calculations

Abstract

Objective: To compare bladder and rectum doses of computer calculations and in vivo dosimetry with thermoluminescent dosimetry (TLD) in patients treated with high dose rate brachytherapy for gnaecological malignancies, and to verfy the correctness of computer calculations. Material and Methods: In this study, bladder and rectum doses are calculated and compared with two dosimetry systems in 24 pateients who were treated with high dose rate brachytherapy with Gammamed 12i (with irridium micro source) unit for gynaecological malignancies in Istanbul University Oncology Institute between October 2006 and May 2007. First, anteroposterior and lateral orthogonal films are obtained and are used for calculations of bladder and rectum points with Abacus Treatment Planning System (TPS); secondly measurements are taken at same points with in vivo TLD dosimetry by using TLD chips (Fimel-LTM dosimetry system with rood LiF (GR 200 A)) previosly calibrated with Cobalt 60. Results: The differences between the measured and calculated doses for bladder and rectum were %0.71-%18.58 (mean: %7.06) and %1.28-%12.59 (mean: %6.16), respectively. Conclusion: The comparison of calculated doses from orthogonal films and in-vivo readings using TLD were compatible with the literature. As a result, the planning computer can be accurately used for the calculations of both treatment and reference point doses.