Approximately 4000 women per year in the United States require radiotherapy during pregnancy. This report presents data and techniques that allow the medical physicist to estimate the radiation dose the fetus will receive and to reduce this dose with appropriate shielding. Out‐of‐beam data are presented for a variety of photon beams, including cobalt‐60 gamma rays and x rays from 4 to 18 MV. Designs for simple and inexpensive to more complex and expensive types of shielding equipment are described. Clinical examples show that proper shielding can reduce the radiation dose to the fetus by 50%. In addition, a review of the biological aspects of irradiation enables estimates of the risks of lethality, growth retardation, mental retardation, malformation, sterility, cancer induction, and genetic defects to the fetus.

The sperm production of 25 patients with Hodgkin's disease treated with mechlorethamine, vincristine, procarbazine, and prednisone (MOPP) chemotherapy was studied retrospectively. All but two patients also received radiotherapy treatment to pelvic and/or non-pelvic fields. Sperm counts were obtained from patients treated either with three or fewer (MOPP-2 group) or with five or more (MOPP-6 group) chemotherapy cycles. Recovery of spermatogenesis following treatment-induced azoospermia was significantly higher among the MOPP-2 patients (Mann-Whitney rank sum test, p = 0.001). Patients in this group who did not receive pelvic irradiation appeared to have greater recovery rates (p = 0.06). The results suggest that three cycles of MOPP chemotherapy represent a maximum exposure compatible with the recovery of spermatogenesis.

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On radiobiological grounds, a therapeutic advantage should result when total body irradiation (TBI) in preparation for bone-marrow engraftment is given as a fractionated course, rather than as a single exposure at logistically reasonable dose rates. This is because cells of hemopoietic origin in general show less capacity for repair of sublethal radiation injury than do cells of other organs. Dose-limiting lung tolerance, in the context of fractionated TBI, is estimated to be at least 12 Gy (without correction) in increments of 2 Gy regardless of dose rate. A practical method for delivering TBI using a high-energy linear accelerator is described.

Irradiation of a tissue-metal interface with 13 MeV to 20 MeV electrons results in an increased dose to the tissue on the entrance side of the metal. Ionization measurements were made with a thin-window parallel-plate chamber to determine the magnitude of the dose enhancement as a function of incident electron energy, thickness and atomic number of metals introduced into the electron beam. The presence of a metal resulted in a dose ranging from 6% to approximately 50% greater than that measured with no metal in the beam. Most of this increase in dose may be eliminated by the addition of 1-2 g/cm2 of low Z material between tissue and metal.