The American team evaluated 593 survivors of acute lymphoblastic leukemia (the most common form of childhood cancer) who had been treated with then-standard cranial radiotherapy: In adulthood, approximately one third had significant deficits in fertility. Fertility was measured as conceiving a first pregnancy or fathering a pregnancy, and the results were compared with those for a control group of 409 brothers and sisters of survivors.

"These results are surprising. We didn't expect radiation to the brain at the doses commonly used would cause fertility problems." said Julianne Byrne, Ph.D., lead author of the study. "Since the radiation effects have not been thoroughly evaluated until this point we'll now have to investigate the mechanisms in the brain that control fertility."

Previously, researchers had known that direct radiation could damage ovaries or testes, but they had thought that cranial radiation was probably harmless with respect to reproduction. This epidemiological study, the largest of its kind to be reported, looked at the chance of a successful first pregnancy for female survivors or fathering a first pregnancy for male survivors. The researchers found high-dose cranial radiation treatment at approximately age nine years for males and around puberty for females was a contributing factor to later infertility. All other age ranges of treated patients did not appear to be adversely affected.

"The study doesn't show evidence of a problem if they were treated early in life or later in adolescence." explains Byrne. "There is just this window of vulnerability that seems to have affected these former patients."

To be eligible for the study, the survivors were treated between 1970 and 1987 and were at least 18 years old at time of fertility follow-up.