Download Digital chest radiography

Title: Digital chest radiography: Collimation and dose reduction
Author: Jeanne Debess, Karen Johnsen and Henrik Thomsen
Overall purpose: Quality improvement of basic radiography focusing on
collimation and dose reduction in digital chest radiography.
First aim was to evaluate the collimation of digital chest radiography and
second aim was to analyze the impact of collimation on dose to thyroid,
breast and stomach.
Methods and Materials
A retrospective study of digital chest radiography was performed to evaluate
the primary x-ray tube collimation of the PA and LAT radiographs. Collimation
data from one hundred eighty-six self-reliant female patients between 15 and
55 years of age were included in the study. In addition the dose area product
(DAP) was recorded from the radiographs. The clinical research was performed
between September and November 2014 where 3rd year radiography students
collected data in four Danish x-ray departments using identical procedures
under guidance of clinical supervisors (Fig 1.) None of the data was personally
identifiable. Optimal collimation, two centimeters on all sides, was determined
by European (1) and regional Danish guidelines. The areal between current
and optimal collimation was calculated.
The experimental research was performed in December 2014 on a Siemens
Axiom Aristos digital radiography system DR using 150 kV, 1,25 -3,3 mAs and
SID of 180 centimeters using an anthropomorphic phantom (Alderson
Radiation Therapy Phantom) and Thermoluminescent dosimeter (TLD). The
TLDs were prepared by and readings conducted at the University College of
Northern Denmark, Department of Radiography, Aalborg Denmark using Rados
RE-2000 and IR-2000 TLD reader with batch homogeneity < 5%. Eight control
dosimeters were used to record the background radiation, which was
subtracted from the measurements.
Absorbed point dose to risk organs right breast, thyroid and stomach were
measured at different collimations with steps of two to four centimeters. For the PA
position two TLD tablets were placed in the right breast: one in a lateral (I),
(Fig. 2) and one in a medial centered position (II). Third TLD was placed in
right thyroid (III) and the fourth in the place of curvature minor of the
stomach (IV), (Fig. 3).
The Alderson phantom was placed PA and x-ray was centered on the middle of
the seventh thoracic spine. The light beam measure was used to ensure the
different collimations (Fig 4). Six exposures were conducted for each
collimation with new TLD for every exposure. The radiographs were evaluated
with respect to DAP, positioning and exposure parameters at the workstation
fig. 6.
For the statistical analyses the SPSS software package was used
(PASW Statistics 22 (version 22.0.0, SPSS Inc., Chicago, IL). Descriptive
statistics included t-test for group differences with respect for different
collimations.
Result
Clinical study
Data from 186 included PA chest radiographs on self-reliant women showed a
mean age of 40 years and mean DAP value of 2,3 (min 1.0 -max 7.3). Only
half of the PA radiographs were correct positioned (Fig. 6).
The retrospective measurements of the original not post processed chest
radiographs showed that 76 % to 90 % had excessive not collimated areas
depending on side. Especially the not collimated area from sinus phrenicocostalis to border was excessive (Fig 7).
Table 1. Radiation dose measured at different collimation
(95%CL)
Body parts
Breast I
Breast II
Radiation absorbed point dose micro Gy: Mean
Correct
collimatio
n
+ 2 cm
collimati
on
+ 5 cm
collimati
on
+ 8 cm
collimati
on
16.6
(14.019.2)
10.8
(8.8-128)
16.0
(12.719.3)
11.3
(10.212.4)
15.5
(14.4-166)
NA
10.5
(9.611.4)
NA
+10.2 cm
collimation
NA
NA
17.8
(16.8Thyroid III 18.8)
11,2
(9.8Stomach IV 12.6)
17.8
(16.818.9)
11.7
(11.112.2)
18.3
(17.519.2)
12.7
(11.813.5)
17.8
(16.818.9)
13.8
(13.014.6)
18.0
(17.3-18-7)
14.0
(13.1-14.9)
Phantom study
Table 1. shows the results from the experimental study as showed a significant
increase of 25% (p<0.01) in point dose to the stomach at 10.2 cm excessive
collimation. No increased dose was found for the other organs, which may
relay of the position of the TLD tablets that already where very close to the
collimation border at correct collimation. We found that DAP values increased
with 54% (p>0.01) from correct to 10.2 cm excessive collimation.
Conclusion:
Quality of basic radiography with respect to collimation and dose reduction in
digital chest radiographs can be improved. From 76 % to 90 % of the
evaluated radiograph had excessive collimation and should be reduced as this
digital chest radiograph is one of the most common examinations with 641,561
examinations performed on Danish departments of medical imaging in 2013
(2). Pervious studies evaluating lumbar spine radiographs found likewise larger
collimation than acceptable (3,4). The radiation dose of 0.1 mSv for the
individual patient is relatively low, but due to the large number of studies, the
collective radiation dose can be significant (5,6). Therefore, a reduction of the
dose for each patient focusing on the ALARA (as low as reasonably achievable)
principle is important (6). It is especially essential to improve the collimation
from sinus phrenicostalis to border as the TLD result showed a significantly
increase in dose of 25 % to the stomach with lack of proper collimation.
Correct positioning and collimation of digital chest radiographs can reduce the
radiation dose significant to the patients and by that improve the quality of
basic radiography.
Litteratur
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radiographic images. Radioprotection 1998;32(1):73.
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"præbillede" og færdigt PACS billede, samt læring og faglig udvikling.
2011;1(1):1-138.
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