TLD as a tool for remote verification of output for radiotherapy beams : 25 years of experience

The University of Texas M.D. Anderson Cancer Center (UTMDACC) has extensive experience with thermoluminescent dosimetry (TLD) as a quality assurance tool for output and energy monitoring of radiation therapy beams. Over the past 25 years the TLD results of the monitored institutions, commissioning data for TLD readers, the characterization data of lithium fluoride TLD-100 powder and the records of a quality assurance program of the system have accumulated. Nearly 1600 TLD sessions over the past 7 years on a cobalt unit reveal an accuracy in dose determination of 0.9% (one standard deviation). This represents a measure of the best achievable accuracy for TLD measured therapy doses. Based on this experience the windows of acceptability may be tightened from 5% in dose to 3% and 5 mm in electron depth to 3 mm.