Development of normal tissue damage in the rat subsequent to thoracic irradiation and prior treatment with cancer chemotherapeutic agents.

The effect of combined modalities (radiotherapy-chemotherapy) on the development of long-term normal tissue damage was investigated in rats. Animals received single I.P. injections of Hank's balanced saline solution, adriamycin (ADR, 1.0 mg/kg), bleomycin (BLM, 10 units/kg), or dihydroxyanthraquinone (DHAQ, 3.0 mg/kg); and/or irradiation of the chest with 25 MV x-rays (12 Gy) at 0, 43, 93, or 199 days after drug treatment. Only animals treated with DHAQ displayed appreciable toxicity, with more animals dying at less than 200 days when radiation was added at 0 or 43 days. Although animals treated with BLM or radiation exhibited evidence of lung damage (histologically by 199 days and radiographically by 300 days), their survival was not compromised. The simultaneous administration of x-ray and BLM produced enhanced effects as compared to either agent alone. These results demonstrate an enhancement of normal tissue damage by combined treatment with radiation and chemotherapeutic agents, not only for acute toxicity but also for long-term effects. This damage was ultimately expressed as alteration of lung structure (histologically and radiographically) in the case of BLM, and as animal lethality in the case of DHAQ. In addition, there was a reduction in the degree of enhancement observed as a function of the separation in time between treatment with chemotherapeutic agents and subsequent irradiation. These factors should be considered when combined modality therapy is used for treatment of cancer in the thoracic region.