Speaker
Description
Background and Aims
Carcinoma during pregnancy presents a complex clinical challenge, requiring a balance between optimal maternal treatment and fetal safety. Radiotherapy is generally avoided during early pregnancy because of potential developmental risks; however, technological advances have improved treatment precision and reduced unintended radiation exposure.
This study evaluates fetal exposure to out-of-field radiation doses by comparing photon and proton radiotherapy. It also proposes the development of a fast-case catalogue based on Monte Carlo simulations using the International Commission on Radiological Protection (ICRP) pregnant female computational phantoms.
Methods
Mesh-type Computational Phantom Models for Pregnant Women (PfMRCPs), based on ICRP Publications 145 and 156, were used for dosimetric assessment. These anatomically realistic phantoms are designed for radiological protection and dose evaluation studies.
Secondary fetal doses were calculated using PHITS and MCNP Monte Carlo codes across multiple clinical scenarios, considering tumor location, gestational stage, and treatment modality.
Results
In photon radiotherapy, most fetal dose originates from internal scattered radiation within the mother, while approximately 10% results from leakage radiation from the accelerator head. External abdominal shielding may help reduce leakage-related exposure.
In proton therapy, secondary neutrons are the dominant contributor to fetal dose, with evaporation neutrons accounting for approximately 90% of the neutron component. Secondary photons contribute roughly 20% of the total fetal dose.
Fetal dose depends on tumor location, distance between the fetus and the treatment field (with no direct beam exposure), stage of pregnancy, and type of proton therapy facility (which may cause dose variations of up to 10%).
Conclusions
The ICRP Pregnant Mesh-type Computational Phantoms provide a valuable tool for rapid preliminary fetal dose assessment without additional radiation exposure. Given limited clinical data and the absence of standardized proton therapy protocols in many countries, developing a Monte Carlo–based fast-case catalogue could support informed clinical decision-making in pregnant oncology patients.