Infertility Risk After 3.7 GBq of Radioactive I-131 Treatment
The risk of infertility following a 3.7 GBq dose of radioactive I-131 is relatively low, with most patients maintaining fertility, though there may be a temporary decline in fertility markers that typically recover over time.
Effects of I-131 on Reproductive Function
Male Fertility
- Spermatogonia are highly sensitive to radiation, with doses as low as 0.1 Gy leading to short-term cessation of spermatogenesis 1
- Doses of 2-3 Gy affect spermatogonial stem cells and cause long-term azoospermia 1
- Doses of 6 Gy can deplete the spermatogonial stem cell pool and cause long-term or permanent infertility 1
- Leydig cell insufficiency and testosterone deficiency have been described with much higher radiation doses of 20-24 Gy 1
Female Fertility
- Radioactive iodine (I-131) is classified as having "intermediate risk" for female fertility, with studies showing a decline in anti-Müllerian hormone (AMH) levels after treatment 1
- RT-related ovarian follicle loss already occurs at doses of <2 Gy 1
- The effective sterilizing dose decreases with increasing age, ranging from 16 Gy at 20 years to 14 Gy at 30 years 1
Clinical Context of 3.7 GBq I-131 Treatment
- A dose of 3.7 GBq (100 mCi) of I-131 is commonly used for thyroid cancer treatment following thyroidectomy 2
- This dose is considered standard for patients with distant metastases from differentiated thyroid cancer, though doses may range from 3.7-7.4 GBq (100-200 mCi) 1
- For neuroendocrine tumors, I-131-mIBG activities typically range between 7.4 and 11.2 GBq administered at 3-6 month intervals 1
Infertility Risk Assessment
- The 3.7 GBq dose of I-131 delivers radiation primarily to the thyroid tissue and tissues that concentrate iodine 3
- While I-131 is classified as having "intermediate risk" for fertility effects, the percentage of patients becoming permanently infertile at this dose is not precisely quantified in the available guidelines 1
- Based on radiation dose-response relationships, a single 3.7 GBq dose would be expected to cause temporary effects on fertility in some patients, but permanent infertility would be uncommon 1
- The radiation from I-131 can affect DNA in proliferating cells, which may include germ cells, but the effect is dose-dependent 4
Risk Mitigation Strategies
- All cancer patients of reproductive age should receive complete oncofertility counseling as early as possible in the treatment planning process 1
- Sperm cryopreservation before initiation of I-131 treatment is standard of care and should be discussed with male cancer patients 1
- For female patients, options may include oocyte or embryo cryopreservation, ovarian tissue cryopreservation, or ovarian transposition depending on individual circumstances 1
- Gonadal shielding during treatment may help reduce radiation exposure to reproductive organs 1
Conclusion
While specific percentages are not clearly defined in the guidelines, the available evidence suggests that most patients receiving a single 3.7 GBq dose of I-131 will maintain their fertility, though temporary effects may occur. The risk increases with higher cumulative doses, older age (particularly in women), and pre-existing fertility issues. Fertility preservation options should be discussed with all patients of reproductive age before I-131 treatment.