SU‐FF‐T‐315: Determination of the Energy Correction Factor for TLD‐100 in Electron Beams Relative to 60Co

Purpose: Thermoluminescent dosimeters (TLDs) are used to measure absorbed dose to water by calibrating them to a known dose from [formula omitted], a NIST traceable standard. Energy correction factors were measured that enables the conversion of TLD measured absorbed dose from [formula omitted] 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 from [formula omitted]. Annealed TLD‐100 chips (3 mm × 3 mm × 1mm) were irradiated using [formula omitted] 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 both [formula omitted] 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 to [formula omitted]. 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.