| TLDs (ThermoLuminescent Dosimeters) are small pieces of crystalline material used in radiation therapy to verify the radiation dose cancer patients receive. University of Virginia Radiation Oncology clinic TLD results must be fully trustworthy so physicians can confidently monitor and determine a patient's treatment. A systematic investigation of major factors affecting TLD response and accuracy was carried out. The factors investigated were dose response, energy response, and fading response for two types of TLDs.; The supralinear dose response of LiF:Mg,Ti and slightly sublinear dose response of LiF:Mg,Cu,P is documented. In energy response, LiF:Mg,Ti over-responds 46% at 33 keV while LiF:Mg,Cu,P under-responds by 10–20% in the kilovoltage region. Fading of LiF:Mg,Ti was measured at 9% in 63 days while the output of LiF:Mg,Cu,P enhanced by 8% 23 days after irradiation. Overall accuracy at the 95% CL is 2.18% for LiF:Mg,Ti and 4.09% for LiF:Mg,Cu,P. Confidence in UVa Radiation Oncology TLD measurements was enhanced with the use of improved procedures.; The improvements include reading LiF:Mg,Cu,P with a neutral density filter in the TLD reader, labeling of TLDs with identifying numbers, and use of a circular annealing tray for cooling. LiF:Mg,Cu,P releases about thirty-four times more light than LiF:Mg,Ti, and a neutral density filter prevents saturation of the TLD reader. Labeled TLDs are easier to work with, resolve mix-ups, and increase accuracy by allowing TLDs to be read always in the same orientation (although labeling slightly reduces the light output). TLDs all cool at the same rate on the circular tray, which maintains consistent TLD sensitivity between TLDs and multiple uses. The improved University of Virginia TLD procedure is documented. |
