The influence of lung and bone dosimetry on the choice of radiation energy for total body irradiation.

Abstract

The radiation absorbed dose to lung and bone is of importance for total body irradiation performed prior to bone marrow transplantation for hematologic malignancies. The measurement and calculation of radiation absorbed dose to low density materials such as lung has been discussed in several publications and most total body irradiation procedures account for the increased radiation dose to the lung. However, radiation absorbed dose to bone and soft tissues within bone is not calculated and is assumed to be the same as the dose to soft tissues. Because the bone is different in both density and atomic number from soft tissues, radiation dose calculations are more complex for bone than for lung. As the energy of the radiation beam changes, the dose to heterogeneous tissue varies. This variation of the radiation dose is investigated for radiation beams ranging in energy from 60Cobalt to x-ray beams produced at 18 MV. The radiation absorbed dose to soft tissues within bone is found to increase relative to the dose to soft tissue for higher megavoltage radiations, while at the same time there is a decrease in lung dose. Therefore, since for total body irradiation procedures the target tissues are the soft tissues within bone, a higher dose to those tissues would be an advantage.