ABSTRACT
The accuracy needed in dosimetry should be considered in view of the requirement for dose delivered to the target volume, for which, in general, the required relative standard uncertainty levels between 3% and 5% have been quoted in International Atomic Energy Agency (IAEA) Technical Report Series No. 398 (TRS-398). The quantity of interest in radiotherapy is absorbed dose to water. Relevant quantities such as biological response and isoeffective dose are also defined with reference to absorbed dose to water. Absorbed dose to water at a reference point in a field that contains a representative set of beam-shaping elements is then a relevant quantity for beam monitor calibration, and dose calculations can be based on relative beam models and output factors. Calorimeters provide the most direct method to measure the quantity of interest in reference dosimetry for radiotherapy, absorbed dose to water.
