Objectives: The aim of this work was to compare the doses in critical organs, treatment duration, patient comfort and personel workload during total body irradiation carried out alternatively with a Cobalt 60 and with 15 MeV photons at linear accelerator. Patients and methods: Twenty consecutive patients irradiated with a Cobalt unit and twenty irradiated with 15 MeVphotons in a linear accelerator were used for comparison of the dose delivered. Each irradiation was repeated eight times during four consecutive days up to a total dose of 12.6 Gy in the whole body (below lOGy in the lungs). Lateral fields were used in six fractions, and anterior-posterior fields in two fractions. An electron boost to the thorax wall was added. Doses were calculated and measured in-vivo in ten transverse sections. Results: For the patient taken as an example doses in the middle of the lungs were 10.7 Gy for Co-60 and 11.2 Gy for 15MeVphotons without compensators and 9.6 Gy, 9.6 Gy respectively when compensators were applied. Mean doses in the lungs in the group were 9.5 Gy for Co-60 and 9.7 Gy for X 15MeV, respectively. Duration of the treatment was shorter with the use of the 15MeVthan that with Co-60 by about 20%. Repositioning of the patient during two fractions with the use of X 15 MeV could be eliminated and therefore the patient's comfort increased.

Keywords: TBI, Radiotherapy, dosimetry, BMT, dose homogeneity