The radiation damage sustained by the ovaries seems to be strictly dose-dependent; there is no threshold dose. Even a radiation dose of only 2 Gray is reported to destroy 50% of the oocytes. A dose of 10 Gray is highly likely to result in amenorrhea.
The uterus and the endometrium are much less radiosensitive than the germ cells. Although radiation of the pelvis reduces the uterine volume and the thickness of the endometrium, the consequences for a subsequent  pregnancy are limited.
A radiation dose of below 10 Gy did not produce a miscarriage in 5 patients after chemotherapy and whole body irradiation (Sanders et al., Blood, 1996, 87:3045-52). Irradiation with 10-14 Gy led to an abortion in 6 out of 16 pregnancies (38%), while 20-35 Gy applied to treat a Wilms’ tumor resulted in an abortion in 9 out of 40 pregnancies (22%) (Hawkins et al., Int J Cancer, 1989, 43:399-402). The risk of premature birth is also increased after radiotherapy. 5 out of 8 pregancies were ended prematurely after chemotherapy and whole body irradiation (Sandes et al.). After radiotherapy for Wilms’ tumor, the weight of the babies was 300 g lower on average than that of non-irradiated controls (Hawkins et al.). The cause of these miscarriages and premature births are presumed to be reduced uterine elasticity due to irradiation-induced fibrosis and damage to the uterine vessels.

The germ cells of the testicles are more radiation-sensitive than those of the ovaries. A radiation dose as low as 0.2-1.2 Gray will result in oligospermia after 9-18 months (Rowley et al., Radiat Res, 1974, 59: 665-78). A dose of 10 Gy causes so much damage that spermatogenesis is only partially restored after 10 years. Whole body irradiation to prepare for a bone marrow transplant leads to permanent testicular dysfunction in most patients, although the remaining sperm production should often be sufficient to produce a pregnancy with the help of artificial insemination (Rovó et al. ;Blood, 2006, 108: 1100-1105).

However, the testosterone-producing Leydig cells are relatively resistant to radiation. Only a dose upwards of 20-30 Gy will lead to such a permanent drop in testosterone levels that the patient may require testosterone substitution.