QUALITY CONTROL OF BREAST IRRADIATION WITH THERMOLUMINESCENT DOSIMETER

Abstract

Objective : Radiation therapy is the one modality of treatment in breast cancer. The important process in radiotherapy is patient positioning that should remain the same for a course of treatment in 25 fractions. The aim of this work is to measure the patient dose during external beam irradiation with the thermoluminescent dosimetry (TLD) to observe the dose delivered to assure the reproducible of patient positioning throughout the course of radiation treatment. Materials and Methods : The TLD-100 chips (LiF, 3.2 3.2 0.89 mm3) were calibrated at 100 cGy with 6 MV photon beam of Varian Clinac 21EX. The TLD chips were loaded into the plastic tube with 3 chips per tube. Ten patients in breast cancer irradiated with 3 dimensional conformal tangential fi eld techniques were studied. Five TLD tubes were attached on the skin surface of patient along the cross line in the center of the radiation fi eld and three tubes were placed on the contra-lateral breast; medial, middle and lateral border. The gentian violet was marked at the patient skin to align the TLD tube, the TLD tubes must be placed at the same position in the next measurement. The frequency of one patient position verifi cation with TLD measurement is 10 times for 25 fractions of a treatment course. Results and Discussion : The uncertainty of TLD dose measurement was 3.78% with 95% confi dence level. The maximum variation of TLD dose measurement in each point on the patient surface for 10 times irradiation was 3.8% for irradiated breast, which was comparable to the uncertainty of TLD. So the result illustrated more reproducible of the patient positioning acquired from less variation of dose obtained. The points that showed high dose difference in irradiated breast and contra-lateral breast illustrated the misalignment of TLD due to the patient’s anatomy. The less dose difference occurred in the fi xed position of TLD. Conclusion : The TLD dose measurement can be used to investigate the reproducibility of patient positioning in breast cancer.