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SU‐FF‐T‐315: Determination of the Energy Correction Factor for TLD‐100 in Electron Beams Relative to 60Co
Author(s) -
Junell S,
Kunugi K,
DeWerd L
Publication year - 2009
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1118/1.3181795
Subject(s) - thermoluminescent dosimeter , dosimeter , linear particle accelerator , irradiation , materials science , dosimetry , absorbed dose , dose profile , thermoluminescence , nuclear medicine , physics , optics , nuclear physics , beam (structure) , medicine
Purpose: Thermoluminescent dosimeters (TLDs) are used to measure absorbed dose to water by calibrating them to a known dose from60 Co , a NIST traceable standard. Energy correction factors were measured that enables the conversion of TLD measured absorbed dose from60 Co to absorbed dose from 6, 9, 12, 15, and 18 MeV electron beams. Method and Materials: Energy correction factors for LiF TLD‐100 (LiF:Mg, Ti) have been determined experimentally as the ratio of thermoluminescent response in electron beams from a linac over the response from60 Co . Annealed TLD‐100 chips (3 mm × 3 mm × 1mm) were irradiated using60 Co and 6, 9, 12, 15, and 18 MeV electron beams from a linac. TLD irradiations were carried out in liquid water with water tight Virtual Water™ TLD holders. Using Ion chamber measurements following the AAPM's TG‐51 protocol, doses delivered to the TLDs for both60 Co and linac irradiations were verified. Results: The experiments showed a average energy correction factor of 0.95 for TLD‐100 chips for 6, 9, 12, 15, and 18 MeV electron beams relative to60 Co . TLD's measured the energy correction factors for electron beams with good precision in a single experiment, with the standard deviation of the mean for the energy correction factors found in each experiment ranging from 0.3% to 0.5%. However, the TLDs were found to be less precise across multiple experiments. The standard deviation of the energy correction factor from experiment to experiment ranged from 2% to 5%. Conclusions: The ability to verify and maintain strict quality control is a fundamental necessity in a radiation treatment facility. External secondary audits are an essential part of a quality assurance program. Energy correction factors allow for TLD's to provide an inexpensive and convenient method to perform external secondary audits of high energy electron beam absorbed dose calibrations.