Dosimetry of CBCT: methods, doses and clinical consequences

The use of Cone beam CT (CBCT) systems for Image Guided Radiotherapy is rapidly expanding in the developed world. With its use comes concern for the increased risks of additional radiation exposure. Quantification of the imaging dose is necessary in order to report, optimise and justify CBCT exposures. This article reviews the current methods of dose measurement and calculation including dose measurements in cylindrical phantoms, use of point dosimeters in anthropomorphic phantoms, calculation of dose using mathematical phantoms and calculation of individualised patient dose using Monte Carlo and model based techniques. Typical doses from commercial systems are reported and the clinical consequences, both risks and benefits, of using CBCT based IGRT reviewed briefly.