Estimation of radiation dose (long version)

unkindnesskindUrban and Civil

Nov 15, 2013 (3 years and 11 months ago)

93 views

Estimation of radiation dose (long version)

Effective dose (E, measured in mSv) in CT of the abdomen and pelvis is influenced by several
factors, some of which are estimated based on available measurements and technical
considerations rather than being act
ually measured. Factors include tube voltage (V), dose (D,
tube current


time product), weighted, effective CT dose index (CTDI
w,eff
,

measured in mGy per
100 mAs per slice) for a given collimation as documented by the CT scanner software, weighting
factor

P
B

for the standardized, 32
-
cm
-
diameter body phantom applied for measurements of
radiation dose, scanner
-
specific correction factor k
CT

, conversion factor f
mean

for body region and
gender (i.e., the abdomen and pelvis in a male or female patient), and s
can length (L, measured
in cm) along the long axis of the patient

s body [
39,40
]. For the four
-
row CT scanner applied
here, V was 120 KVp, CTDI
w,eff,
was 9.0 mGy per 100 mAs per slice at 1 mm collimation, and 7.6
mGy per 100 mAs per slice at 2.5 mm collimation (CT scanner software), P
B

was 0.49 [
39
], k
CT

was 1.0 [
39
], a
nd f
mean

was 0.0072 for male patients and 0.0100 for female patients [
41
]. The
formula [
39,40
],

E = D/100
×
CTDI
w,eff
×
1/P
B
×

k
CT
×
f
mean
×
L,

yielded results as demonstrated in Table A, below. For estimation of radiation dose, it was
assumed that scan length (
L) would be 15 cm for the adrenals, kidneys, and upper ureter in both
male and female patients, 45 cm in male and 40 cm in female patients from the diaphragm to the
symphysis pubis, and 35 cm in male and 30 cm in female patients from the diaphragm to the
d
istal ureter.