Abstract Basic dosimetry as well as patient dosimetry are considered. The following items concerning the basic beam dosimetry are discussed: dosimetry calibration, phantom material, beam quality and depth dose measurements in TBI conditions. Dose to the patient should be specified to the midplane of the abdomen but dose to the lung should be estimated for each patient. In vivo, dosimetry is strongly recommended for determination of dose homogeneity, as well as to check patient position, reproducibility of treatment and instabilities in dose rate during TBI. Many physical problems are associated with in vivo dosimetry. All influences on the detector response have to be considered and the detectors must be calibrated for TBI conditions.