Dose Does Not Equal Dose

Energy dose: The irradiation of a lifeless object is adequately described by the energy dose. This represents the radiation energy (J; joules) that is absorbed per unit mass (kg) and is measured in units of grays (1 Gy = 1 J/ kg). Any impact the radiation may have on an organism is completely ignored by this descriptor.

Equivalence dose: The effect of x-rays on living organisms is described by the equivalence dose. To calculate it, the energy dose is multiplied by a correction factor that represents the biological effect of radiation. It is measured in units of sieverts (Sv). For the usual x-rays this correction factor fortunately equals 1, which is why 1 Sv = 1 Gy = 1 J/ kg. The energy and equivalence dose are of course difficult to measure in any living organism let alone a human being. The patient would have to swallow dosimeters, which would have to be read out after the intestinal passage— a little impractical, to say the least.

Personal dose: To quantitate the effect of radiation on an individual, the personal dose was introduced—also measured in sieverts (Sv). It represents the equivalence dose at specific representative locations on the body surface where you can wear a dosimeter. Now dose becomes a parameter you can work with. Dose limits have been

I Nonstochastic Effect

Medical Ray Doses

Fig. 5.2 These historical photographs show the development of radiation injury to the hand of Max Levy-Dom, who acquired it over the duration of several years as chief of one of the first radiology departments in the world. Before starting an examination he used to test the function of the "Roentgen" tube—unfortunately using his own hand as a test object.

Fig. 5.2 These historical photographs show the development of radiation injury to the hand of Max Levy-Dom, who acquired it over the duration of several years as chief of one of the first radiology departments in the world. Before starting an examination he used to test the function of the "Roentgen" tube—unfortunately using his own hand as a test object.

agreed upon (Table 5.2). To put these into a proper perspective, here is a comparison: The natural radiation exposure of the gonads is about 1.1 mSv/year, while radiation exposure to this area due to human activities (from medical exposures, fallout from atomic bombs, etc.) equals approximately 0.6 mSv/year.

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Responses

  • Antti
    How useful is dose equivalence in radiology?
    5 years ago

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