Dosimetry of low and medium energy X-rays

Formalisms are evaluated for absorbed dose determination in two photon energy regions of interest in radiotherapy and radiobiology, i.e.: X-rays generated at tube voltages in the range 50-100 kV (low energy X-rays) and in the range 100-300 kV (medium energy X-rays). For low energy X-rays, the quantity to be determined under reference conditions is the photon absorbed dose to water at the surface of a water phantom. This quantity shall be determined from measurement of air kerma free-in-air (in the absence of the phantom) and application of appropriate conversion factors. For medium energy X-rays, the quantity to be determined under reference conditions is the absorbed dose to water at the reference depth (2 cm) in a water phantom. Absorbed dose at other positions in the phantom shall be obtained by performing relative measurements with a field instrument and can be related to the value determined at the reference point. The reference chamber shall be calibrated in air in terms of air kerma at the Primary Standard Dosimetry Laboratory in a beam of X-rays. The quality of the calibration field shall be as close as possible to that of the user's primary beam.

https://doi.org/10.25030/ncs-010

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