Previous reports of histological investigation of radiation-induced heart injury in human are limited. It is important to identify radiation-induced heart injury and must be differentiated from other heart disease. Histological attempt was made to clarify heart injury following irradiation in this paper. The interval between irradiation and the time of demonstrable histological changes was investigated.
The study material is consist of eighty-three autopsies. Major primary neoplasms were breast cancer, lung cancer and mediastinal tumor. In 43 out 83 autopsies, the heart was irradiated and in others, the heart was not irradiated.
Also sixty-eight dd-strain mice were used for microautoradiographic study. The results were as follows :
1) Histological changes of the heart was obserbed in 27 of 43 cases received irradiation.
2) The limit of tolerance dose of the heart indicating histological changes was 1220 ret in human.
3) The latent period without histological changes was 2.7 months after onset of radiation therapy.
4) Judging from the uptake of3H-TdR cardiac proliferative cells in mice, the latent period was shorter than one investigated microscopically.
5) Heart injury following re-irradiation for the recurrence, or following combination therapy of radiation and chemotherapy, especially MMC, was observed more intensively.
6) In 5 of 15 cases which were treated with MMC alone, the histological findings were similar to the radiation-induced heart injury, since MMC is radiomimetic substance.
7) Although some investigators believed that radiation injury to the heart muscle is direct, in our study it seems that damage is secondary to radiation-induced changes of the vasculoconnective tissue.
8) In our study, only one who received four courses of radiation therapy died of radiation-induced heart injury. Even in this case, the tumor was not present in the heart or any other place at autopsy. But this might not occur if radiation therapy is planed well initially.