Calibration of clinical dosimeters and their proper use

Accuracy of absorbed dose estimate in radiotherapy is dependent on the accuracy of the clinical dosimeter, which depends on accuracy in calibration and proper use of the dosimeter. In addition, if the treatment results are to be comparable among institutions, there must be uniformity in clinical dosimetry. The Radiological Standards Laboratory of the Bhabha Atomic Research Centre, Bombay, is designated as a collaborating centre by the WHO and IAEA for Secondary Standard Radiation Dosimetry (SSDL) for India and neighbouring countries. The SSDL Centre accepts clinical dosimeters of reference class for calibration against the national standard. The various characteristics for which dosimeters are tested, the calibration procedure, and care and maintenance of dosimeters are described. The validity of calibration factors under field conditions and calibration of field instruments against local standard are discussed. The SSDL Centre also has a programme of intercomparison of absorbed dose on teletherapy units in the country to ensure uniformity in absorbed dose. (M.G.B.)