| Abstrakt: |
When making in vivomeasurements, particularly of doses to patients undergoing total body irradiation, considerable differences are often found between the results obtained using semiconductors and thermoluminescent dosemeters (TLD) (Naudy, 1981; Aukett, 1985; Welsh & Stedeford, 1986, personal communication).The variation in sensitivity of lithium fluoride with dose and with photon energy was established when the use of the material was first suggested (Cameron et al, 1961) and is now well known (Fowler & Attix, 1966; McKinlay, 1981).Variations with dose-rate have been observed for semiconductor detectors (Lavin, 1968; Grüssel & Rikner, 1984). The response of semiconductor detectors also varies with photon energy (Wright & Gager, 1977; Dixon & Ekstrand, 1982; Johansson, 1982; Rikner, 1985). Corresponding variations in sensitivity with depth might be observed for both thermoluminescent and semiconductor dosemeters. Such effects have already been observed for different types of semiconductor detectors (Gager et al, 1977; Rikner & Grüssel, 1983).In order to investigate this possibility the two types of detector were compared with an ionization chamber at a series of depths including both build-up and build-down regions. Measurements of the variation in sensitivity with dose and dose-rate were also made so that these could be eliminated from the results. The 6 MV linear accelerator used at this centre for total body irradiation was used throughout.The semiconductors used were Therados type EDP 10 used in conjunction with a DPD 5 dose monitor. |
