Girls who are exposed to low doses of radiation therapy to the head while being treated for a brain tumor or other form of cancer may experience difficulty in bearing children when they are older, according to a study conducted at the St. Jude Children’s Research Hospital in Memphis, Tennessee.
While physicians were aware prior to the study that higher doses of radiation for such conditions have the potential to destroy brain cells that control the way the ovaries produce eggs, “it was not known that more modest doses can possibly have an effect on fertility,” notes Daniel Green, MD, co-author and an oncologist with St. Jude’s.
To conduct the study, Green and his colleagues sent questionnaires to about 3,600 women who had had cancer as girls, during the period spanning 1970 through 1986. Questionnaires were also sent to about 2,100 of the womens’ sisters, and all subjects were asked about any pregnancies they might have had. Most of the women in the former group, about six out of 10, had been afflicted with leukemia or a brain tumor; others, with cancers of the lymph nodes, bone, or muscles. None of the subjects had been subjected to radiation of their ovaries.
About three of every 10 former cancer patients had been pregnant at least once, compared to about five out of 10 of their sisters, the researchers report in the medical journal Fertility and Sterility. This small difference, they say, could have been due simply to chance. Moreover, while Green and his group did not analyze how many times women tried to become pregnant, the actual pregnancy rate was significantly lower for some of the subjects, not only those who received the highest doses of radiation to the pituitary glands and hypothalamus.
The highest doses involved more than 27 units of radiation, known as grays. But women exposed to at least 22 units of radiation also had significantly lower odds of pregnancy—one-third fewer pregnancies compared to survivors who had never had been treated with radiation. A dose of 22 grays is more than 200,000 times higher than the amount of radiation in an average chest x-ray.