Impact of pulmonary metastases of the R1H-tumour on radiation tolerance ofrat lung

Purpose: The aim was to investigate the influence of pulmonary metastases o f the R1H oil the radiation response Of the lung of the WAG/Rij rat. Material and methods: Three groups of animals were metastases-free animals treated with fractionated irradiation of the lungs; metastases-hearing anim als receiving no irradiation: and metastases-bearing animals treated with f ractionated irradiation initiated 14, 21 or 28 days after induction of pulm onary metastases of the R1H-tumour by i.v. injection of viable tumour cells . metastases were thus treated at various well-defined sizes. Total doses o f 20 60 Gy were applied in fractions of 2 Gy within 11 days. Complication r ate and survival time were used as endpoints. Results: About 2 months after onset of irradiation treatment, animals had t o he sacrificed because of severe respiratory distress either caused by irr adiation-induced lung damage (median 57 days, range 36 77 days), or because of development of lung metastases (65, 20 160 days). A decrease of the ED5 0 (dose required to induce lethal lung damage in 50% of irradiated animals) , was determined for metastases-hearing animals. This effect increased with metastatic volume. Conclusions: The results suggest the presence of tumours in the lung decrea sed the lung tolerance to radiation. This efect call hardly be explained by a reduction in functional lung volume by metastatic volume.