The value of radiation pathology in understanding the radiation effects in normal tissues and tumors is stressed in developing curative radiotherapy. A theory of cell radiosensitivity is presented based on cellular proliferation, differentiation and life span. From this base, concepts of tissue and organ radiosensitivity are developed utilizing the knowledge of tissue organization, cell kinetics and microcirculation. Through a series of paradigmatic charts and drawings an attempt is made to explain different clinical manifestations of radiation reactions on the basis of similar histopathologic changes. Possible future directions for radiation research to explore are outlined.

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Recent improvements in radiation therapy of some malignancies in lower abdominal sites are leading to a prolongation of life in persons of child-bearing age. These successes require an evaluation of the possible undersirable consequences of the unavoidable gonadal irradiation that occurs in these cases. A review of radiobiological data from experimental animal studies and retrospective clinical studies suggests that in most instances human gonadal exposures in both sexes are insufficient to cause permanent sterility, because the exposures are fractionated and the total gonadal dose is much less than 600 rads. As a consequence, return of fertility must be anticipated, and the worrison questions of radiation-induced genetic damage in subsequent pregnancies must be addressed. This review did not substantiate this fear, because no case reports could be found of malformed infants among the progeny of previously irradiated parents. Some experimental studies suggest that radiation-damaged spermatogonia are self-destructive, but any evidence for this phenomenon in the ovary is nonexistent. We suggest that the difference between fact and theory here may be the mathematical result of the interplay of low probability for occurrences and the few patients who until now have survived long enough for study.

Very little is known concerning the radiation affects on the spermatogenic epithelium of the human. This was studied by serial semen analysis in male patients with Hodgkin's disease. Dosimetry in vivo indicated that with an average daily dose of 12.0 rads, the testes receive a total dose of 140 to 300 rads during the inverted Y‐inguinal field treatment. Of 10 consecutive patients entered into the study, all were documented as being aspermic in the immediate post‐irradiation period. Comparison is made with those cases of accidental single dose irradiation of the testes reported in the literature. The fractionated irradiation caused aspermia for longer periods and more consistently than similar or larger single doses. This is new human evidence which supports the observation in animals that a particular mode of fractionated irradiation may be both more effective and efficient than single dose irradiation in producing the above specified endpoints.