Pregnancy outcomes in childhood cancer survivors according to uterine radiation dose and other factors.

Objectives: This study aimed to describe pregnancy and maternal outcomes according to radiation doses received to the uterus during photon beam therapy in the French Childhood Cancer Survivor Study (FCCSS) cohort.

Methods: Of the 7670 5-years survivors, 1159 women treated by radiotherapy and with no hysterectomy, followed between 2006-2018 were included. Uterus dose were reconstructed within phantoms modelling patient's anatomy in treatment position. A statistical analysis was performed including demographic information, treatment variables and co-factors.

Results: Among 1,159 women, 297(25.6%) had at least one pregnancy, of whom 105/297(35.3%) had a uterine dose of Dmedian>1Gy. The proportion of ectopic pregnancy, spontaneous and medical abortions was 20.3%(101/498) and increased to 39% if Dmedian_uterus>20Gy, versus 12% reported in the French's general population. When medical pregnancy terminations were excluded significant associations with an increase in risks were found for women who were older than 40 at the time of pregnancy and Dmedian_uterus>20Gy. Two women whose entire uterus received over 40 Gy had one pregnancy, resulting in a live birth. One woman passed away due to haemorrhage during delivery, treated at age 16 with D80%uterus=35Gy. No other delivery-related deaths were reported.

Conclusion: Assessing the dose to the uterus for pelvic irradiation treatments is necessary and volume receiving 20 Gy should be minimised. Even if pregnancy is feasible after really high dose received on the uterus (Dmean>40Gy), a close obstetrical monitoring is recommended and home delivery should be contraindicated due to the risk of vital hemorrhage.