OBJECTIVE: Radiotherapy during pregnancy is clinically challenging due to concerns about fetal radiation exposure. Proton therapy (PT) with pencil beam scanning can reduce out-of-field dose compared with photon therapy; however, secondary neutron production requires accurate fetal dosimetry. Approach: This study presents the design, material characterization, and computational modeling of two anatomically realistic pregnant anthropomorphic phantoms, MaTORI10 and MaTORI30, representing 10 and 30 weeks of gestation and developed for fetal dose assessment in PT. Candidate materials for lung, soft tissue, and bone-including commercial phantom materials, QA materials, and novel 3D-printed or castable polymers-were evaluated using MCNP 6.2 Monte Carlo simulations and compared with reference pregnant-tissue compositions. Depth-dose distributions, neutron yields, and out-of-field neutron spectra were analyzed to characterize radiological behavior. Suitable materials were implemented in physical phantoms constructed by integrating 3D-printed components and cast bone into an ATOM® female phantom. Pregnancy geometries from the University of Florida pregnant phantom library were merged with ATOM CT and surface scans to generate anatomically realistic models with detector inserts. Voxelized computational versions were generated from CT and surface scans and implemented in TOPAS 3.8. A virtual PT brain irradiation plan (78-116 MeV, 10 cm range SOBP, 5 cm modulation, 3 cm radius), with and without a range shifter (RS), was used to quantify in-field and fetal doses. Main Results: Material testing showed substantial variability, primarily driven by differences in hydrogen content and density. Both phantoms were successfully constructed and validated by CT imaging. For MaTORI30, modeled fetal dose was on average 29% higher without RS and 21% higher with RS compared to reference materials; for MaTORI10, increases of 10% and 18% were observed. Significance: The MaTORI10 and MaTORI30 phantoms provide the first anatomically detailed, pregnant anthropomorphic phantoms whose tissue-equivalent properties were computationally characterized for fetal dose assessment in PT. These phantoms provide a platform for experimental and Monte Carlo-based assessment of fetal dose, facilitating safer radiotherapy and optimal planning for pregnant patients. .
Saint-Hubert et al. (Wed,) studied this question.