Development of a computational pregnant female phantom and calculation of fetal dose during a photon breast radiotherapy

Abstract

Background The incidence of carcinoma during pregnancy is reported to be 1:1000–1:1500 pregnancies with the breast carcinoma being the most commonly diagnosed. Since the fetus is most sensitive to ionizing radiation during the first two trimesters, there are mixed clinical opinions and no uniform guidelines on the use of radiotherapy during pregnancy. Within this study the pregnant female phantom in the second trimester, that can be used for radiotherapy treatment planning (as DICOM data), Monte Carlo simulations (as voxelized geometry) and experimental dosimetry utilizing 3D printing of the molds (as .STL files), was developed. Materials and methods The developed phantom is based on MRI images of a female patient in her 18th week of pregnancy and CT images after childbirth. Phantom was developed in such a manner that a pregnant female was scanned “in vivo” using MRI during pregnancy and CT after childbirth. For the treatment of left breast carcinoma, 3D conformal radiotherapy was used. The voxelized geometry of the phantom was used for Monte Carlo (MC) simulations using Monte Carlo N-Particle transport codeTM 6.2 (MCNP). Conclusions The modeled photon breast radiotherapy plan, applied to the phantom, indicated that the fetus dose is 59 mGy for 50 Gy prescribed to the breast. The results clearly indicate that only 9.5% of the fetal dose is caused by photons that are generated in the accelerator head through scattering and leakage, but the dominant component is scattered radiation from the patient’s body.

Development and validation of the low‐cost pregnant female physical phantom for fetal dosimetry in MV photon radiotherapy

“…38 The model of the accelerator, as well as the voxelized Tena phantom setup, are described in previous publications. 25,28,[39][40][41] The phantom materials used in MC simulations were as described in the previous section. Exact elements and weight fractions are given in Supplemental Table 2.…”

“…For the model verification, 3D conformational radiotherapy (RT) treatment plan was used as described previously 25 . Virtual Tena phantom was used as the calculation dataset.…”

“…MC simulations of the radiotherapy plan were performed using Monte Carlo N‐Particle transport code version 6.2 38 . The model of the accelerator, as well as the voxelized Tena phantom setup, are described in previous publications 25,28,39–41 . The phantom materials used in MC simulations were as described in the previous section.…”

“…This study demonstrated the development of a low‐cost, physical pregnant female phantom using commercially available materials. This phantom is based on the previously published computational phantom, developed by our group 25 . Though MC simulations are valuable research methods, their setup and computational time can take a significant amount of time 26,27 .…”

“…For those reasons, we decided to make the physical representation of the Tena phantom since we already have prepared both voxelized forms and .STL (eng. “Standard Tessellation Language”, stereolithography) files suitable for 3D printing of the phantom, in the previously published study 25 . As proof of principle, we performed experimental validation of the physical phantom comparing experimentally determined fetal doses, using radio photoluminescence (RPL) dosimeters, with simulations during a breast radiotherapy treatment of 50 Gy.…”