Background : Estimation of the radiation dose to the fetus is essential for the assessment of radiation risks and benefits to pregnant patients undergoing radiological examinations. During the past decade, the global twinning rate has soared resulting from embryo assistance and increased delivery age. However, to the best of our knowledge, radiation dosimetry in multiple pregnancies from radiological imaging has never been reported before.

Purpose : The purpose of this study is to develop personalized computational models for twin fetuses based on clinical CT images of real pregnant patients and to estimate personalized radiation doses for twin fetuses from abdominal/pelvic CT examinations.

Methods : Personalized computational phantoms representing pregnant females with twins at the second and third trimesters were constructed based on CT images of two pregnant patients. Monte Carlo calculations were performed using the MCNP transport code and three validated CT scanners to estimate the radiation dose of twin fetuses during abdominal and pelvic CT examinations.

Results : The absorbed fetal organ dose was calculated and compared between twins. For the same patient, the absolute difference in fetal organ dose between twins varies between 0.63% and 39.64% with an average value of 12.85%. The estimated total‐body dose differences for twin fetuses were 11.55% and 7.51%, respectively, for pregnant patients at 22 and 30 weeks gestational age.

Conclusion : The variations of body weight and organ mass affect the absorbed dose of twin fetuses. Personalized computational models provide more accurate fetal radiation dosimetry estimates for pregnant patients with twins. This work also contributes to a better understanding of model‐induced uncertainties in external radiation dosimetry for the developing fetus.