SU-E-T-101: Two-Peak Ratio Method in LiF Thermoluminescent Dosimeters to Determine the LET and the Separate Absorbed Dose Components in a Mixed Radiation Field for Applications in Radiation Therapy

Abstract

Purpose: Sensitivity difference between the two main temperature peaks to LET radiations in LiF TLDs was used to extract information in mixed radiation fields on their LET and their high and low LET absorbed dose components. Method and Materials:LiF TLD 600 and 700 chips were inserted in tissue equivalent phantoms and irradiated with LET radiation from 0.2 to 66 KeV/micron. The ratio of areas under the main peaks at 210 and 280, 0, C was used to investigate their LET dependence and determine the dose in the detectors for different types of radiation. The neutron calibration was obtained with the Am-Be source at Argonne National Laboratory while LET dependence was determined by irradiation in photon, proton, neutron, and carbon therapy beams. By separately determining the area under the two peaks the dose delivered by the LET components in a mixed radiation field was obtained. To determine the secondary dose components for 18 MV photons, the high thermal neutron sensitivity of, 6, Li in TLD 600 provided the thermal neutron dose while TLD 700 provided the fast neutron and photon doses. Results: The two peak ratio varied from 1 to 6.5 over the range of KeV/micron, and a difference in LET was observed for one of the neutron beams. Peak analysis of the neutron irradiated detectors showed agreement within 3 and 15% between the measured and calculated neutron and photon doses, respectively. Measurements of the secondary dose for 18 MV were 20 and 0.1 % of the photon dose for fast and thermal neutron, respectively. Conclusion: Ratio of high to low temperature peak areas was determined as a function of LET for beam qualities used in radiation therapy. Two-peak analysis provided the high and low LET doses in mixed radiation fields such as neutron therapy and secondary radiation from 18 MV photons.