Photon-beam radiotherapy in pregnant patients: can the fetal dose be limited to 10 cGy or less?

PURPOSE: To estimate fetal dose and its components from three-dimensional conformal radiotherapy for several malignancies presented during pregnancy.

MATERIALS AND METHODS: Fetal dose was measured from radiotherapy for Hodgkin's lymphoma and for tumors in the region of nasopharynx, breast and lung. Anthropomorphic phantoms were used to simulate an average pregnant patient at the first, second and third trimesters of gestation. Thermoluminescent dosemeters (TLD) were employed for fetal dose measurements. Phantom exposures were also performed to estimate fetal dose due to head leakage, scatter from collimators and beam modifiers and scatter generated inside the phantom (Din). All treatments were delivered for 6 MV photon beams.

RESULTS: Radiotherapy of Hodgkin's lymphoma resulted in a fetal dose of 5.6-57.9 cGy depending upon the gestational age and the distance between the fetal level and the field edge. The corresponding dose ranges for treatment of nasopharyngeal, breast and lung cancer was 4.0-17.1 cGy, 3.9-24.8 cGy and 5.7-74.3 cGy, respectively. The Din at the first trimester of gestation was always smaller than 10 cGy for all examined malignancies. Pregnancy progression resulted in Din values above or below 10 cGy depending upon the treatment site and gestational age.

CONCLUSION: This study provides data about the fetal exposure and the contribution of Din to the total fetal dose from conformal radiation therapy. The Din knowledge prior to patient's irradiation enables radiation oncologists and medical physicists to decide whether fetal dose may be limited to 10 cGy or less with or without the introduction of special shielding materials.