Is Electron Beam Intraoperative Radiotherapy (ELIOT) Safe in Pregnant Women with Early Breast Cancer? In Vivo Dosimetry to Assess Fetal Dose

Electron beam intraoperative radiotherapy (ELIOT) is a new technique permitting breast radiotherapy to be completed in a single session. Since ELIOT is associated with much reduced irradiation to nontarget tissues, we carried out a study on nonpregnant breast cancer patients to estimate doses to the uterus during ELIOT to better evaluate the possible use of ELIOT in pregnant breast cancer patients. We performed in vivo dosimetry with thermoluminescence radiation detectors (TLDs) in 15 premenopausal patients receiving ELIOT to the breast (prescribed dose 21 Gy) using two mobile linear accelerators. The TLDs were positioned subdiaphragmatically on the irradiated side, at the medial pubic position, and within the uterus. A shielding apron (2 mm lead equivalent) was placed over the viscera from the subcostal to the subpubic region. TLDs showed mean doses of 3.7 mGy (range 1-8.5 mGy) at subdiaphragm, 0.9 mGy (range 0.3-2 mGy) pubic, and 1.7 mGy (range 0.6-3.2 mGy) in utero, for beam energies in the range 5-9 MeV. These findings indicate that ELIOT with a mobile linear accelerator and shielding apron would be safe for the fetus, as doses of a few mGy are not associated with measurable increased risk of fetal damage, and the threshold dose for deterministic effects is estimated at 100-200 mGy. We conclude that studies on the use of ELIOT in pregnant women treated with conservative breast surgery are justified.