Mobile shielding evaluation on the fetal dose during a breast radiotherapy using Monte Carlo simulation

Area of Science:

• Radiotherapy physics and dosimetry
• Medical physics and radiation protection
• Fetal radiation dose assessment

Background:

• Out-of-field dose evaluation is critical in radiotherapy, especially for pregnant patients due to fetal radiosensitivity.
• Accurate dosimetry is essential to minimize risks to the developing fetus during maternal cancer treatment.

Purpose of the Study:

• To evaluate the effectiveness of different shielding strategies in reducing out-of-field radiation doses to a fetus during radiotherapy.
• To analyze dose reduction using specific shields (M1, M2) on a pregnant anthropomorphic phantom (Maria) with a Varian Clinac 2100c linear accelerator at 6 MV.

Main Methods:

• Simulations using MCNPX code for medial and lateral projections.
• Utilized an anthropomorphic phantom (Maria) representing a pregnant patient.
• Compared open field collimation (10x16cm²) with multileaf collimator (MLC) and analyzed the impact of added shields (M1, M2).

Main Results:

• Shields (M1, M2) effectively reduced doses to the fetus, amniotic sac, and placenta.
• The M2 shield reduced fetal dose by approximately 43% with open field collimation, primarily in lateral projections.
• Multileaf collimator (MLC) significantly lowered doses to the fetus and amniotic sac compared to open fields; minor dose increases observed in maternal organs (eyes, thyroid, brain).

Conclusions:

• The use of protective shields is essential for minimizing radiation dose to the fetus and critical structures during radiotherapy.
• Shielding strategies, including MLC and specific phantom shields, demonstrate significant potential for improving fetal radiation protection in radiotherapy.