Background: In most cancer cases, the treatment
choice for a pregnant patient is radiotherapy. In these
patients, the abdomen is usually not exposed;
therefore fetus exposure is due to peripheral dose
(PD). The purpose of this study was to estimate the
fetal dose (the maximum PD in each pregnancy
stage) for modalities available and to fabricate and
evaluate a generally applicable fetal shield. Materials
and Methods: PD values were measured for brain,
breast and mediastinum irradiation in a whole body
anthropomorphic phantom using a NE 2571
ionization chamber. An external shield was then
designed to reduce the fetal dose to the standard
dose limit, 5 mSv. Results: The range of PD values as
a function of distance from the field’s edge were as
follows 1) 9.4-259 cGy for Mantel field; 2) 6.5-95 cGy
for chest wall irradiation with 10 MeV electrons, 3)
8.5- 52.5 cGy for tangential field with Co-60 and 4)
4.8-7.8 cGy for brain radiotherapy with 9 MV photon.
PD values for the same setups using the fetal shield
were as follows: 1) 1.4-22 cGy, 2) 0.5-4 cGy, 3) 1.5-5
cGy and 4) under 1 cGy. Conclusions: The measured
PD data sets can be used to estimate fetal dose for
specific treatment setups and pregnancy stages. The
use of external shield designed in this research
reduced the fetal dose effectively to under the threshold
(a 70-90% reduction), except for the final stages
of pregnancy in Hodgkin’s patients
