Fertility impairment is one the most significant adverse effects in patients treated with radiation to the head and neck area, pelvic region and spine. Radiotherapy of head and neck may damage the central nervous system, leading to deficiency of gonadotropins, possibly hyperprolactinemia (high levels of prolactin, inhibiting the secretion of sex hormones) and disruption of gonadal function. Radiotherapy in the pelvic area directly damages the gonads and impairs their function. Gonads and germ cells are among the most radiosensitive tissues and even low doses of radiation may lead to their dysfunction and cell death.
Oocytes (egg cells) are extremely radiosensitive. Therefore, radiation easily damages the DNA of oocytes leading to their atrophy (cell death) and diminished ovarian reserve. There are several factors affecting ovarian fertility impairment: radiation dose, age at time of the exposure and size of the irradiated area. Moreover, women treated with radiation to the pelvic region or abdomen are in a greater risk of adverse pregnancy outcomes and complications, such as placental disorders, spontaneous abortions, low birth weight and difficulty with conceiving, due to radiation-induced damage to the uterus.
The testicle is one of the most radiosensitive tissues, and even the lowest doses of radiation may lead to its temporary dysfunction and oligospermia (reduced sperm count). Also, the dividing cells in the testes, the spermatogonia, are very radiosensitive. Therefore, even a dose below 1 Gy (Gray) may lead to a significant reduction in the number of spermatogonia and daughter cells. Due to the lifespan of developing sperm cells, during the first 50-60 days the sperm count is reduced to 50% (at a 1.5–2 Gy dose), and may later drop even further, eventually leading even to azoospermia (no sperm cells present in the semen). Higher radiation doses may lead to permanent or long-term azoospermia and infertility. Potential restoration of fertility requires some of the dividing cells to survive, and the time required before the sperm count is restored heavily depends on both the single dose and the total dose of radiation.