Answer to Question #830 Submitted to "Ask the Experts"

Q

What precautions would you take when irradiating a pregnant breast-cancer patient?

A

There are any number of considerations here and we will try to deal with each of them briefly. The first consideration is whether or not the treatment can be postponed until the fetus is at a later gestational age. This discussion needs to take place between the patient, her physician, and the radiation oncologist. These considerations involve the patient and her entire family and need to take into account the state of the patient's disease and the risks involved. We will assume that these discussions have taken place and it has been decided by the patient and her physicians that treatment is necessary. There are fundamentally two ways in which radiation can reach the fetus, leakage radiation from the head of the machine and internal scatter from the patient's own organs. Consultation should be sought with the certified radiation oncology physicist who will advise on the feasibility of constructing blocks, essentially body shields, above the abdomen during the time of treatment. The leakage radiation from the treatment machine is limited by the National Council on Radiation Protection and Measurement's recommendation to 0.1% or 1/1,000 of the dose rate in the primary beam at 1 meter from the target in the head of the machine. With no additional shielding, if a patient received a total dose of 5,000 rad or 50 Gy, the remainder of the patient's body would receive a total of 5 rad or 5 cGy from the leakage radiation. It may be possible to reduce this number further with the use of supplemental shielding as designed by the radiation oncology physicist. The second source of dose is internal scatter from organs within the patient's body. It is usually not possible to reduce this dose significantly. However, the radiation oncology physicist can calculate the dose which would be received by the fetus from the treatment and, in consultation with the radiation oncologist, suggest any modifications of the treatment fields which would lower the total dose to the fetus. Other types of treatment which may be employed, such as chemotherapy, may also result in potential deleterious effects and it is essential that the patient thoroughly discuss all options with her physician and ask for genetic counseling if she is considering becoming pregnant after treatments are finished. Jean St. Germain, CHP