Does Accelerated Partial Breast Irradiation Decrease Scattered Fetal Dose in Pregnant Women As Compared to External Beam Radiation?

This is a prospective clinical study to compare the scattered fetal dose during Accelerated Partial Breast Irradiation (APBI) versus External Beam Radiation Therapy (EBRT). The scattered dose to the lower anterior abdominal wall of 14 consecutive patients treated with Accelerated Partial Breast Brachytherapy (APBI) were recorded using film badges. The film badges were placed on the anterior abdominal wall midway between the umbilicus and symphysis pubis. This is comparative to a 16 week pregnancy. None of the treated women were pregnant. APBI used SAVI devices of different sizes. The dose per treatment was 340 cGy prescribed to one cm around the lumpectomy cavity. One cm bolus was added on top of the film badges. No shielding was attempted for the first 4 cases. For the following 10 cases a lead apron was applied on top of the abdomen and pelvis. The scattered dose was also measured using the same way for another 10 patients treated with external beam radiation using 3D/IMRT to the whole breast. The dose prescribed was 180 cGy per fraction. No abdominal shielding was attempted. The doses were recorded for only five treatments and multiplied by 5 to account for a total dose of 45 Gy. The measured doses for 14 patients treated with APBI (4 without shielding and 10 with lead apron) were analyzed and compared to the doses collected for 10 patients treated with EBRT). Our data showed that APBI patients received much lower doses as compared to patients treated with EBRT. Adding a lead apron had decreased the exposure dose by more than 50% (p = 0.01). The average dose for APBI patients was 9.2 cGy (without shielding) and 4.4 cGy (with shielding) as compared to 15.5 cGy for patients treated with EBRT. The recorded doses were closely related to the distance between the SAVI device and the film badges, (p = 0.05). Also, there was close correlation between the patient weight and the recorded doses (p = 0.05) with heavier patients having lower doses. APBI contributes less scattered dose to the fetus as compared to whole breast radiation. The scattered dose is much easier to block due to the lower energy used. The longer the distance between the SAVI and the pelvis, and the heavier the weight of the patient, the less the dose recorded.