Brain radiotherapy during pregnancy: an analysis of conceptus dose using anthropomorphic phantoms

The aims of this study were: (a) to determine conceptus dose resulting from brain radiotherapy, (b) to investigate the necessity of using shielding de vices over patient's abdomen during treatment; and (c) to estimate the comp onents of conceptus dose. Radiation doses received by conceptus were measur ed using anthropomorphic phantoms simulating pregnancy at 4, 12 and 24 week s gestation and thermoluminescent dosemeters. All irradiations were perform ed with two lateral and opposed fields approximating the minimum, medium an d maximum held size used during treatment of brain malignancies. For a trea tment course delivering 65 Gy to tumour without using shielding equipment, conceptus dose never exceeded 100 mGy. Appropriate positioning of 5.1 cm of lead over the phantom's abdomen provided reduction of conceptus dose from 26% to 71%, depending upon gestational age, field size and distance from th e field isocentre. The contribution of scatter arising from within the phan tom to the conceptus dose was small compared with that from head leakage an d collimator scatter. Our dosimetric results indicate that the construction of special shielding equipment is not a prerequisite for treating brain ma lignancies during pregnancy. However, based on the concept that exposures i n women of childbearing age should be kept as low as reasonably achievable, we suggest that shielding devices should be used whenever possible.