engleski

The use of glass dosimeter in patient dosimetry

In some materials irradiation induces stable radiation-induced defects, and subsequent illumination of the sample with light stimulates photoluminescence from those defects. The phenomenon of photoluminescence is the excitation, via the absorption of light, of an electron in a crystal defect within the material, resulting in transition of the electron from the defect's ground state to an excited state. Relaxation back to the ground state results in the emission of luminescence (termed “radiophotoluminescence”, RPL), the intensity of which is proportional to the concentration of excited defects (and to the absorbed dose). It was recognized that many synthetic materials show this effect. The one selected as the most economical and practical for large-scale manufacture was a silver-activated phosphate glass which was first proposed as dosimeter for use in accidental dose range in 1953. After many years of investigations, the formulation called FD-7 from 1971 is still a basis for different types of RPL glass dosimeters due to its favourable dosimetry characteristics and stable and reproducible production. Recently, Asahi Techno Glass Corporation, Shizuoka, Japan developed a new system “Small Element System Dose Ace” using very small glass element (FD-7 glass) for various applications: dose verification for radiotherapy and diagnosis, animal irradiation experiments, dose distribution measurements etc. There are basically two types of the small glass element GD-300 series, with (GD-351 and 352M) and without (GD-301 and 302M) energy compensation Sn filters. For patient dosimetry in diagnostic radiology the emphasis is on justification of medical procedures and optimisation of radiological protection. The importance of patient dose measurements is especially pronounced for CT and interventional radiological procedures. Radiation dosimetry in radiotherapy has 2-fold goal: ensuring the quality of treatment as well as the radiation protection of the patients. The development in new techniques in both, diagnostic radiology and radiation therapy increases importance of dosimetry measurements taking into account possible late effect of radiation. RPL small glass elements types containing energy compensation filter are suitable for medium and low energy X-rays as used in diagnostic radiology and types without filter for high energy photon fields in radiation therapy. The special reader, FGD-1000 is the high sensitivity reader with the nitrogen gas laser as a source of ultraviolet light excitation which can perform a continuation pulse oscillation. It is possible to read-out continuously 20 samples. The reader is automatically calibrated using the internal calibration glass. It is possible to measure doses in standard dose range (10 µGy-10 Gy) and high-dose range (1 Gy-500 Gy). In the present work, the results of the RPL glass elements as used in patient dosimetry are reviewed and compared with other dosimetry methods.

Glass dosimeter; RPL; Patient dosimetry

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