Absorbed dose to water standards established by water calorimetry at the LNE-LNHB for medium energy X-ray

Nowadays, the absorbed dose to water for kilo-voltage X-ray beams is determined from standards in terms of air-kerma by application of international dosimetry protocols. New standards in terms of absorbed dose to water have just been established for these beams at the LNE-LNHB. A specific calorimeter was developed to do measurements at low depth in water, in order to fulfill the reference conditions required by the international dosimetry protocols for medium-energy X-ray. This new calorimeter was used to measure the absorbed dose rate in water at a depth of 2 cm for six medium-energy X-ray reference beams with a tube potential from 80 kV to 300 kV. The relative standard uncertainty obtained on the absorbed dose rate by water calorimetry is lower than 0.8%, whereas the one given by application of protocols based on air kerma is around 2.5%. (authors)