Abstract
Decision for radiotherapy during the first trimester of pregnancy may occur, as patients may not realize their pregnancy at the very early stage. Since radiation dose can affect fetal development, the aim of this study was to evaluate fetal dose and associated deterministic effects and risks to the fetus from breast cancer radiotherapy of an 8-week pregnant patient. PHITS (Particle and Heavy Ion Transport code System) Monte Carlo simulation and the J-45 computational pregnancy phantom were used to simulate breast cancer radiotherapy from a 6 MV TrueBeam linear accelerator using the three dimensional-conformal radiotherapy (3D-CRT) technique with a prescribed dose to the planning target volume (PTV) of 50 Gy. Once the fetal dose was evaluated, the occurrence of the deterministic effects and risks for developing stochastic effects in the fetus were assessed using the recommendations of NCRP Report No. 174, AAPM Report No. 50, and ICRP Publication 84. The fetal dose was evaluated to be 3.37 ± 2.66 mGy, suggesting that the fetus was expected to have no additional deterministic effects, while the risks for developing cancer and malfunctions were similar to that expected from exposure to background radiation. The comparison with the other studies showed that accurate consideration of fetal position and size was important for dose determination in the fetus, especially at the early pregnancy stage when the fetus is very small.
Highlights
The differences of doses in the organs at risk obtained by the Monte Carlo simulation and the treatment planning system were in the range of 6.38–92.31% for the left lung, total lung, esophagus, heart, right lung, and spinal cord, respectively (Table 2)
The larger dose differences were observed for the organs at further distances from the field edge. Such dose differences between Monte Carlo simulations and treatment planning systems have been reported in the literature in relatively good agreement with this work, e.g., the dose differences in the organs at risk have been reported to range from 10–70% for the heart, right lung, esophagus, and left lung, respectively, for a breast cancer treatment plan [12]
The absorbed dose in the fetus from breast cancer 3D-CRT of an 8-week pregnant patient was calculated for a 6 MV TrueBeam linear accelerator
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Radiotherapy treatment planning for cancer patients considers the in-field radiation dose, including a high dose to the treatment volume for high tumor control and a low dose to normal tissues for reducing tissue complications in order to achieve a high therapeutic ratio. Sometimes pregnant patients may receive radiotherapy, causing additional concern for out-of-field radiation dose outside the treatment volume, because this radiation dose will affect the fetus. The treatment plan must consider both the in-field radiation dose for the patient and the out-of-field radiation dose in order to avoid deterministic effects and minimize the risk of developing stochastic effects in the fetus
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