Dosimeter tissue equivalent

Although the limitations of the method and sophisticated equipment required are likely to restrict the use of the e aq dosimeter to places equipped for pulse radiolysis, the system has some advantage in that its low atomic number makes the dosimeter tissue equivalent. LiF, however, is not exactly tissue equivalent for x-rays of energy below about 100 Kev. its response becomes 20 to 30% too high below 50 Kev. (3). 

Armstrong WA, Facey RA, Grant DW, Flumphreys WG (1963) A tissue-equivalent chemical dosimeter sensitive to 1 rad. Can J Chem 41 1575-1577... 

An important parameter, CT dose index (CTDI, defined as the cumulative dose along the patient s axis for a single tomographic image), should be evaluated at least semiannually at different values of kVp and mA. It is measured by using an ionization chamber or a thermoluminescent dosimeters placed in a tissue-equivalent acrylic phantom simulating head or body. ACR (2007) recommends maximum doses CTDI) of 6 rad (60 mGy) for brain, 3.5 rad (35 mGy) for adult abdomen and 2.5 rad (25 mGy) for pediatric (5-year-old) abdomen. The details of these measurements are available in standard CT physics books. 

If the dosimeter is to be applied in medicine one has further to consider that the material has similar atomic composition as tissue or be tissue-equivalent . 

L-a-alanine, H2NCH(CH3)COOH, is the most commonly used material for ESR dosimetry. Alanine has excellent characteristics for dosimetric purposes in several respects [4] (1) high free radical yield (G-value), (2) short relaxation times so that high microwave power can be applied, (3) linear ESR response with radiation dose up to 5-10" Gy, (4) high stability of the radiation induced free radicals so that the dosimeter can be kept as a document of the radiation dose, (5) tissue equivalence for medical and biological applications, (6) non-destructive read-out of dosimeter so that the dose accumulation at repeated exposures can be monitored. 

The dose equivalents in Faulkner and Harrison (1988) and Faulkner and Marshall (1993) were absorbed dose in tissue using a dosimeter placed at or near the surface of the body (NRPB, 1980). This dose quantity can be converted to deep dose equivalent [i.e., //p(lO)] by multiplying by a factor of 1.07 (NRPB, 1990). The original dose equivalents have been modified by this factor and converted to i7p(10) in this Report. 

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