Evaluation of Fetal Dose in Breast Radiotherapy With Shielding and Wedges

The fetus may be seriously affected by the peripheral dose when a pregnant woman undergoes breast radiotherapy. To quantify this dose, a humanoid phantom was irradiated at the left breast, simulating breast radiotherapy. The phantom, consisting of an adapted manikin (with internal and external materials having densities close to that of water), was irradiated in a 6-MeV X-ray linear accelerator (Clinac 600CD). A shield of blocks and lead slabs was placed around the abdominal region of the phantom. Two types of wedges were used to modulate the beam: a physical wedge and the enhanced dynamic wedge (EDW), both with 30^° angulation. Using a cylindrical ionization chamber of 0.6 cm ³ positioned in the phantom´s fetal region, at the end of breast treatment, the peripheral doses were 3.90-48.67 cGy with the physical wedge and 1.75-13.78 cGy with the EDW. The doses were 3.5 times greater when the physical wedge was used due to scattering by its attenuator material and the increase in the leakage radiation intensity. The use of a shield around the abdominal region of the phantom and the use of the EDW during simulation of the treatment reduced the peripheral doses to tolerable limits from ICRP and AAPM.