Patient-Specific Computational Model and Dosimetry Calculations for PET/CT of a Patient Pregnant with Twins

Abstract

The radiation dose delivered to pregnant patients during radiologic imaging procedures raises health concerns because the developing embryo and fetus are considered to be highly radiosensitive. To appropriately weigh the diagnostic benefits against the radiation risks, the radiologist needs reasonably accurate and detailed estimates of the fetal dose. Expanding our previously developed series of computational phantoms for pregnant women, we here describe a personalized model for twin pregnancy, based on an actual clinical scan. The model is based on a standardized hybrid pregnant female and fetus phantom and on a clinical case of a patient who underwent anF-FDG PET/CT scan while expecting twins at 25 weeks' gestation. This model enabled us to produce a realistic physical representation of the pregnant patient and to estimate the maternal and fetal organ doses from the F-FDG and CT components. The Monte Carlo N-Particle Extended general-purpose code was used for radiation transport simulation. The F-FDG doses for the 2 fetuses were 3.78 and 3.99 mGy, and the CT doses were 0.76 and 0.70 mGy, respectively. Therefore, the relative contribution ofF-FDG and CT to the total dose to the fetuses was about 84% and 16%, respectively. Meanwhile, for F-FDG, the calculated personalized absorbed dose was about 40%-50% higher than the doses reported by other dosimetry computer software tools. Our approach to constructing personalized computational models allows estimation of a patient-specific radiation dose, even in cases with unusual anatomic features such as a twin pregnancy. Our results also show that, even in twins, the fetal organ doses from both F-FDG and CT present a certain variability linked to the anatomic characteristics. The CT fetal dose is smaller than theF-FDG PET dose.

Construction of patient‐specific computational models for organ dose estimation in radiological imaging

“…Other limitations of this work include the few organs considered and the use of only one CT scanner model. The construction of patient‐specific models for accurate dosimetry calculations remains a challenging issue requiring further research and development efforts . Deep learning approaches have brought revolutionary advances in the field of medical image analysis that could be useful for constructing patient‐specific models through automatic segmentation of medical images (body contours and internal organs).…”

Construction of a digital fetus library for radiation dosimetry

“…According to the National Council on Radiation Protection and Measurements Report no 184, 9 in addition to background radiation, the major source of ionizing radiation exposure of the American public is related to the medical exposure. Pregnant females might be exposed to different sources of ionizing radiation, including diagnostic radiology, 1,10–12 radiation therapy, 13,14 and nuclear medicine 3,15–17 procedures. The health effects of ionizing radiation on the embryo/fetus depend on their gestational age: (i) The stage of 3–4 weeks of pregnancy is supposed to be the most likely period to suffer embryo death; (ii) whereas the pregnancy at 8–15 weeks is considered to be the most sensitive for radiation risks of growth retardation, microcephaly, and severe mental disability 18–20 ; (iii) finally, at 16–40‐week gestation, fetal radiation exposure higher than 1.5 Gy can result in both growth and mental retardation 19,20 .…”

Hybrid computational pregnant female phantom construction for radiation dosimetry applications

“…The models were used for radiation dose assessment of fetuses and pregnant patients using positron-emitting radiotracers [23]. In addition, a patient-specific computational phantom was developed for dosimetry calculations using a PET/CT scan of a patient pregnant with twins [24]. Another study by Xie et al [25] demonstrated that patient-specific computational models can be created using an automated deep learning-based segmentation algorithm for retrospective radiation dose evaluation during high-dose procedures in a clinical setting and in research studies involving retrospective data analysis.…”

“…The average pregnant computational phantom [15][16][17][18][19][20][21][22][23][24][25][26] was adopted and recommended by the ICRP as a standard pregnant patient. To date, only a limited number of realistic fetal phantoms have been created for each pregnancy stage to demonstrate the stages of fetal development and intrauterine positioning.…”