The thresholds for permanent sterility in women for prepubeal exposure and premenopausal exposure conditions are

In women, radiation is highly effective at inducing permanent ovarian failure, but there is a marked age dependence insensitivity. The dose required to induce permanent sterility varies from 12 Gy (1,200 rad) prepubeal to 2 Gy (200 rad) premenopausal. Pronounced hormonal changes, comparable to those associated with the natural menopause, accompany radiation-induced sterilization in females.Reference: Eric J Hall Textbook of Radiobiology for Radiologist; 5th edition