Comparison of heavy particle with X-irradiation on the hamster lung.

Important new modalities for cancer therapy are being developed, and one of the most promising is heavy charged particle irradiation. We are currently assessing the effects of 375-MeV/nucleon neon irradiation in the plateau region of ionization compared to 230KVp X-rays on the whole thorax of hamsters. Single dose levels for neon irradiation ranged from 150-1000 rad. Dose levels for X-irradiation ranged from 225-1500 rad. The animals were followed for 1 year after irradiation, and the most useful results emerged, using morphometric methods. One year after irradiation, pulmonary parenchyma and nonparenchyma appear morphometrically unchanged. However, the volume density of pulmonary septums, septal cells, all tissue, connective tissue, and alveolar Type II cells was increased while the volume densities of alveoli, empty alveolar space, and capillary lumens were diminished. Most of these changes were dose dependent not clearly demonstrable until a year after irradiation. The relative biologic effect of neon compared to X-irradiation using this techniques is 1.6-1.8.