Gonadal shields, appropriate collimation of the x-ray beams, and limited
and prudent application of repeat procedures definitely lead to a consider-
able reduction in GSD from medical procedures.
Genetic effects of radiation can be greatly reduced if a time interval is
allowed between radiation exposure and conception. This is the conse-
quence of some repair process after irradiation. It is, therefore, recom-
mended for both men and women that conception should be deferred for
about 6 months after a significant radiation exposure such as a radiation
accident or radiation therapy involving high gonadal exposure. Such delay
in conception is not needed for diagnostic procedures.
Risk Versus Benefit in Diagnostic Radiology and
Nuclear Medicine
Millions of x-ray, dental x-ray, computed tomography (CT), and nuclear
medicine procedures are performed in the United States for the diagnosis
of diseases, and the number is increasing steadily over the years. However,
with the remarkable improvement in the evolving techniques and equip-
ment, the effective dose to the individual and to the population as a whole
is steadily decreasing.
Of all diagnostic radiological procedures, CT scans and fluoroscopic pro-
cedures give the highest effective doses, whereas dental and chest x-rays
contribute only minimal effective doses. Gonadal doses are higher with flu-
oroscopic procedures than with head CT, chest x-ray, and dental procedures.
This is primarily due to the fact that the gonads are out of the field of the
latter procedures. It should be noted that the mammographic procedure
contributes only a little to the total body dose compared to the breast. For
obvious reasons, the highest gonadal dose comes from the procedures
involving hips and pelvis. The GSD is about 9.8 mrad (98mGy) for males
compared to 20.9 mrad (209mGy) for females (NCRP 100, 1989).
The doses to different organs from different nuclear medicine procedures
are listed in Table 14.4 and the effective doses in Table 14.5 in Chapter 14.
Radiation dose is always higher with long-lived and b-emitting radionu-
clides. The GSD values for females (1.9 mrad or 19mGy) is almost twice
those of males (1.1 mrad or 10.9mGy) (NCRP 100, 1989).
Risks from diagnostic procedures include both somatic and genetic
effects. Normally, these effects are minimal from diagnostic procedures for
humans because doses from these procedures are considered low. Doses
from nuclear medicine procedures are even lower than those from diag-
nostic x-ray procedures. However, based on the LNT model, there is no
reason to believe that there is no risk from diagnostic exposures, no matter
how small the doses are. There may not be acute effects, but long-term
effects such as carcinogenesis, teratogenic effects from fetal exposure, and
genetic effects in the future offspring can occur. The probabilities of fatal
258 15. Radiation Biology