Optimization of a dosimetric procedure in total body irradiation

The experimental dosimetry of 2 radiotherapy beams produced by a 60Co Picker unit and by a Siemens 4 MV unit, respectively, was analyzed to verify the use of tissue air ratio (TAR) and tissue maximum ratio (TMR) in the computerized planning of total body irradiation (TBI). The use of a small ionization chamber PRO5P Capintec in anthropometric phantoms allowed us to test a computed calculation procedure adopted to reduce both experimental uncertainties and time consumption. The experimental test on the computed procedure was also useful to identify the equivalent fields the patient's body had to be divided into for dosimetric planning. Such dosimetric specifications as average dose to the patient and degree of dose inhomogeneity are calculated when the thickness of compensator filters in perspex is optimized. Following the guidelines reported in ICRU 29, a dosimetric record is presented. In page 1 the target volume is described, in page 2 the provisional treatment planning, and in page 3 the actual treatment planning, checked with in vivo TLD measurements, and the dose specifications for TBI.