Experimental technique
For each projection (AP/PA) the kVp increment was varied by
5 kVp from 75 to 110 kVp. In order to ensure continuity and
minimise error the same imaging plate was used throughout the
study. Image acquisition was repeated three times for each kVp
increment and at each orientation (AP/PA).
Dosimetry
Entrance surface dose (ESD) was measured using a Mult-OMeter
407L (Unfors Instruments, Billdal, Sweden) positioned on
the phantom at the centre of the collimated field. In order to increase
the accuracy of dose measurement the ESD was measured
three times and an average value was calculated. ESD measurements
were converted to effective dose (ED) estimations using the
Monte Carlo dosimetry simulation software PCXMC 2.0 (STUK,
Helsinki, Finland). PCXMC is a computer program for calculating
patients' organ doses and effective doses in medical X-ray examinations
(radiography and fluoroscopy) using Monte Carlo modelling.
13 The doses are calculated in 29 organs and tissues and the
program calculates the effective dose with tissue weighting factors
from the ICRP 103 publication.14
The mean effective (ICRP 103, 2007) and absorbed doses to the
stomach, colon and remainder tissues were recorded, as these are
classified as the three most sensitive tissues irradiated during an AP
lumbar spine radiography.6 Absorbed doses to the ovaries and
testes were also recorded in order to compare findings between the
two projections.