Reirradiation tolerance of the rat heart

Abstract

Purpose : To investigate the influence of reirradiation on the tolerance of the heart after a previous irradiation treatment. Methods adn Materials : Female Wistar rats were locally irradiated to the thorax. Development of caridac function loss was studied with the ex vivo working rat heart preparation (20). To compare the retreatment experiments, initial, and reirradiation doses were expressed as the percentage of the extrapolated tolerance dose (ETD) (1). Results : Local heart irradiation with a single dose led to a dose-dependent and progressive decrease in cardiac function. The progressive nature of irradiation-induced heart disease is shown to affect the outcome of the retreatment, depending on both the time interval between subsequent doses and the size of the initial dose. The present data demonstrate that hearts are capable of repairing a large part of the initial dose of 10 Gy within the first 24 h. However, once biological damage as a result of the first treatment is fixed, the heart does not show any long-term recovery. At intervals up to 6 months between an initial treatment with 10 Gy and subseqeunt reirradiation, the reirradiation tolerance dose slightly decreased from 74% of the ETD ref (at 24-h interval) to 68% 43% of the ETD ref. Treatment of the heart with an initial of 17.5 Gy, instead of 10 Gy, 6 months prior to reirradiation, also led to a further decrease of the reirradiation tolerance dose (< 38 vs. 68% of the ETD ref). Conclusions : The outcome of the present study shows a decreased tolerance of the heart to reirradiation at long time intervals (interval > 6 months). This has clinical implications for the estimation of reirradiation tolerance in patients whose mediastinum has to be reirradiated a long time after irradiation course.