Posted on 31 August 2015
Cancer treatment center Institut de Cancérologie de l’Ouest – René Gauducheau in Nantes turned to France’s national metrology lab for ionizing radiation, LNHB (Laboratoire national Henri-Becquerel), to calibrate for the first time an ionization chamber directly in absorbed dose to water in medium-energy X-ray beams used in radiotherapy.
It is the first time LNHB has transferred its new absorbed-dose-to-water dosimetric reference established using water calorimetry. LNHB designed and built a water calorimeter that can take measurements at a depth of 2 cm, as required by the IAEA TRS-398 protocol. Standard uncertainty on absorbed dose rate to water is less than 0.8%.
Calibrating the ionization chamber directly in absorbed dose to water reduced the uncertainty by a factor of three as compared to the traditional method, which entails calculating the absorbed dose to water calibration coefficient from an air kerma calibration and the use of dosimetry protocols.