Fetal dose estimates for electron-beam treatment to the chest wall of a pregnant patient.

The purpose of this report is to discuss dosimetry and shielding for electron-beam radiotherapy of pregnant patients. Specifically, we have determined fetal dose for a pregnant patient considering electron radiotherapy for a chest wall recurrence of breast cancer. The treatment was simulated using an anthropomorphic phantom, and the measured dose to the unshielded fetus for this plan was 5.3 cGy, a level at which risk to the fetus is uncertain. Therefore abdominal shielding, consisting of 6.6 cm of lead, was used to reduce the dose to the fetus to less than 1.5 cGy, a level considered to be of little risk. We further found that using the lower (instead of upper) variable trimmer bars to define the field edge closest to the fetus resulted in approximately 30% lower dose to the fetus. These results show that it is possible to reduce fetal dose to acceptable limits in electron-beam radiotherapy of the chest wall using the general principles recommended for photon-beam radiotherapy.