Dosimetry
From an evaluation of the dosimetry calculations (Table 4;
Figs. 2e5) it is evident that the PA projection results in a significantly
reduced effective dose for all tube potentials studied. Themean ED reduction was 19.8% (range, 17.9e22.8%). As expected a
trend was noted where kVp increases the ED for both orientations
was seen to progressively decrease.
Individual organ/tissue doses were compared by kVp and between
the AP and PA projections. Itwas evident (Fig. 3A) that the PA
projection reduced the absorbed dose to the stomach by a
maximum 74.0% at 75 kVp and a minimum of 66.9% at 110 kVp. It
was also clear that the PA projection reduced the absorbed dose to
the colon (Fig. 3B). The maximum dose reduction (68.3%) was seen
at 70 kVp with a minimum dose reduction of 56.6% seen at 110 kVp.
The PA projection also reduced the absorbed dose to the remainder
tissues (Fig. 3C). The maximum reduction in absorbed dose was
again experienced at 75 kVp (36.0%) with a minimum reduction of
29.3% at 110 kVp.
With respect to gonadal dose, the PA projection also reduced the
absorbed dose to the testes by a maximum of 24.7% at 70 kVp a
minimum of 8.7% at 80 kVp. The absorbed dose to the testes appears
to increase with an increase in tube potential (Fig. 4A). The PA
projection resulted in a reduction in the absorbed dose to the
ovaries of 22.8% at 70 kVp (maximum) and 3.7% at 110 kVp (minimum)
(Fig. 4B).
Fig. 5 demonstrates the relative (percentage) absorbed dose
reduction to the stomach, colon, remainder tissues, ovaries and
testes across each kVp. Fig. 5 clearly indicates that the most significant dose reduction is to the stomach, followed by the colon
and remainder tissues.