THERMOLUMINESCENCE DOSIMETRY APPLIED TO IN-VIVO DOSE MEASUREMENTS FORTOTAL-BODY IRRADIATION TECHNIQUES

Background and purpose: In total body irradiation (TBI) treatments in vivo dosimetry is recommended because it makes it possible to ensure t he accuracy and quality control of dose delivery. The aim of this work is to set up an in vivo thermoluminescence dosimetry (TLD) system to measure the dose distribution during the TBI technique used prior to b one marrow transplant. Some technical problems due to the presence of lung shielding blocks are discussed. Materials and methods: Irradiatio ns were performed in the Hospital de la Santa Creu i Sant Pau by means of a Varian Clinac-1800 linear accelerator with 18 MV X-ray beams. Di fferent TLD calibration experiments were set up to optimize in vivo do se assessment and to analyze the influence on dose measurement of shie lding blocks. An algorithm to estimate midplane doses from entrance an d exit doses is proposed and the estimated dose in critical organs is compared to internal dose measurements performed in an Alderson anthro pomorphic phantom. Results: The predictions of the dose algorithm, eve n in heterogeneous zones of the body such as the lungs, are in good ag reement with the experimental results obtained with and without. shiel ding blocks. The differences between measured and predicted values are in all cases lower than 2% Conclusions: The TLD system described in t his work has been proven to be appropriate for in vivo dosimetry in TB I irradiations. The described calibration experiments point out the di fficulty of calibrating an in vivo dosimetry system when lung shieldin g blocks are used. (C) 1998 Elsevier Science Ireland Ltd. All rights r eserved.