FIGURE 2
(mGycm)
Mean DLP data for bone SPECT/CT lumbar spine examinations in the
four dose modes on
the T16
scanner 15
Quote
here SPECT/CT
kpkp
pk pkpk pk ppkp
Thick black markers pk
indicate
the mean
pkpk
pkpk pk Boxes indicate the fi rst and third quartiles
Thin lines inside the boxes indicate the median
Whiskers indicate the smallest and largest values
kpkp
pk pkpk
Dashed line indicates
the proposed
NDRL for pk
localisation (moderate dose mode)
ppkp pk pkpk
1800
pkpk pk kpkp pk
pkpk pk ppkp
1600
pk pkpk pkpk pk
1400
kpkp pk pkpk pk
ppkp pk pkpk
1200
pkpk pk kpkp
1000
800
600
400
200
0
Low
(5)
Moderate
(24)
Standard
(33)
Metal
(12)
Dose Mode (Number of Patients
have identifi ed scanners with subtly different
imaging protocols and tube-current modulation
not being switched on! When there can easily be
dozens or more protocols set up on CT scanners,
it is usually impractical to check each one
line-by-line and compare across every scanner,
but simple setup errors will go on to infl uence
doses for many patients. Using patient dosimetry
audit to identify such issues and harmonise
protocols and practices helps identify and avoid
the situation of patients receiving signifi cantly
different radiation doses depending on which
scanner they happen to fi nd themselves on. In
some cases, it might be justifi ed for a particular
scanner to have different protocols, and therefore
give different doses to others, perhaps because it
is used for different clinical conditions (for
example, trauma scans). But where there is no
such reason, harmonisation of protocols is a
simple means of dose optimisation.
CT is also used as standard outside of
diagnostic radiology such as in nuclear medicine
TABLE 1
CT dose modes developed for nuclear medicine in
order of increasing dose
Dose mode
Low
Moderate
Standard
Metal
CT purpose
Attenuation correction
Localisation
Diagnostic CT
Patients with orthopaedic implants
4
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(with SPECT/CT and PET/CT being routine) and
radiotherapy (for treatment planning scans and
on-board imaging for verifying patient positioning
prior to treatment). Only in the past few years has
there been progress in establishing patient
dosimetry audit in these areas. 8–12 In encouraging
recent progress, the Institute of Physics and
Engineering in Medicine (IPEM) has established
working parties that undertook national audit
and published data for nuclear medicine CT 13 and
radiotherapy planning CT, 14 the results of which
were subsequently adopted as UK NDRLs. 5 This
gives very useful data for local results to be
compared against. The rest of this discussion will
be on the efforts based at RRPPS to establish local
systems for patient dosimetry audit in these
areas, including some of the challenges we
encountered and the solutions developed. In the
future, it is hoped similar work will be carried out
for radiotherapy on-board imaging as well.
Nuclear medicine CT
The full results of the initial patient dose audit
were published in the British Journal of Radiology 15
based on the proposed NDRLs which were
available at the time. 16 Data were collected for
adult patients on two SPECT/CT Scanners
(Siemens Symbia T & T16) over November
2014–July 2016 and for a PET/CT scanner (Siemens
Biograph mCT Flow) over April–August 2016.
Initially, we based the audit on the nuclear
medicine examination type (bone scan,
parathyroid, etc) as this matches how the NDRLs
were set out. However, it soon became apparent
that nuclear medicine CT has some complications