Evaluation of the Clinical Use of TLD

RUDBNThermoluminescent dosemeters (TLD) are nowadays widely used in radiation therapy to measure the radiation dose (RUDBN 1971, SUNTHARALINGAM & MANS-FIELD 1971, RUDBN & NILSSON 1973, LINDSKOUG 1974).Information on the absorbed dose delivered is both a control of the therapy unit and a check that the right parameters are being used for adequate treatment of patients.At Radiumhemmet, SIEVERT (1932) began to use routinely for patient dose measurements small ionization chambers (condensed chambers usually referred to as Bg-chambers), which were entirely separated from the reading instrument.High quality Bg-chambers are not commercially available and it is difficult to maintain and increase their number.Therefore, thermoluminescent dosemeters were introduced for the determination of absorbed doses in routine therapy in 1968.During 1970 the number of clinical measurements amounted to 17 OOO of which two thirds were made with TLD and during 1974 the number was 30 OOO of which 98 per cent were made with TLD.The purpose of this report is to describe the routine use of TLD for a wide range of dosimetry applications in radiation therapy, the handling of the dosemeters to obtain high accuracy and the usefulness of making patient dose measurements. Energy dependence of LiF dosemetersAt Radiumhemmet the following facilities are available for treatment: conventional roentgen radiation units (20-200 kV), 6oCo units, accelerators for 6 MV and 42 MV roentgen radiation and 5-39 MeV electrons.It is therefore essential to know the response of the different kinds of LiF dosemeters at the various energies used in order to confirm the absorbed doses given to the patients.The primary calibration of the dosemeters was carried out in a 6oCo gamma ray beam.The ratio Aco=Tco/ DHzO, co of the thermoluminescent signal Tco and the absorbed dose in water D,,,.was also used as the primary sensitivity factor for the other radiation qualities, in the