Use of a 4 MV linear accelerator for whole body irradiation

The use of a 4 MV linear accelerator for whole body irradiation is described in this study. The room size limits the focus to skin distance to 279 cm. At this distance a maximum field length of 162 cm is achieved by: (a) using the diagonal of the beam by rotating the collimator 450; (b) adding a special flattening filter which increases the useful field length. The horizontal beam is directed either laterally (patient supine) or anteroposteriorly (patient on side). The dose heterogeneity for both these geometries was measured in a phantom** loaded with Li2B4O7 thermoluminescent dosimeters (TLD) and film. The lateral treatment geometry causes significantly larger dose heterogeneity than the anteroposterior treatment. Because of the increased dose to the lungs in either one of these treatment geometries, the use of compensators in this region is suggested