Beam filter and compensators during total body irradiation on Cobalt-60

Abstract

Total body irradiation performed with a combination of lateral and anterior – posterior fields was used prior to bone marrow transplantation. Dose discrepancies in a body during lateral fields were caused by different distances from the source to the particular body parts, different thickneses of body sections in ten reference levels and differences in interior tissues density. To improve dose homogeneity a radiation filter and individual compensators were used in the beam.

Dose deviations at the points representing patient's side and midline were counted and measured in a water tank and then for a patient taken as an example. Deviations were measured for the open field, filtered field and for the field with the filter and compensators.

For a patient taken as an example standard dose deviations for all ten sections were 17.0% in midline and 7.1% in side for an open beam and 9.8%, 4.8% respectively for the beam with the filter and compensators. Mean percent deviations from the dose in the central axis were −3.1% (midline) and −2.5% (side) for open, and −0.1% and 0.9% for the filtered and compensated beams, respectively.