radiotherapy/chemotherapy treatment. CT used in isolation cannot always
distinguish tumour progression from radiotherapy damage/necrosis, even up to
Radiographers
several months after the patient has received treatment
14
.
have adopted
Various empirical studies and critical reviews have demonstrated the additional
value of SPECT-CT over stand alone SPECT systems, particularly in cases such as
the roles
lymphoma
21,22
, infection and bone disease
17
. However, there appears to be a
debate relating to the appropriate use of low dose CT for attenuation correction
of referrer,
and/or basic localisation purposes (which were the parameters of a low
performance x-ray scanning device) and higher quality CT data for improved
practitioner
anatomical image quality. Roach et al’s study in 2006
23
was conducted using
a multislice SPECT-CT unit which permitted greater spatial resolution for the
and operator
anatomical data. Although the overall final diagnosis and reporter confidence was
improved using a multislice SPECT-CT unit, the increase over first generation low-
performance SPECT-CT units was minimal.
Diagnosis using diagnostic quality CT
SPECT-CT has a role in diagnosis, particularly when ‘targeted’ SPECT imaging reveals
lesions with no surrounding discernable anatomical landmarks (for localisation)
and also when the internal structure of the SPECT lesion needs additional
radiological (high resolution CT) scrutiny to determine its nature. An example could
Figure 3. Radiation dose from CT
be differentiated thyroid cancer, using whole body imaging with iodine 123 or morphological appearance of the metastases can be clearly located on the
131. Here, the precise localisation of lesions is often not possible because of the diagnostic quality CT image series, giving heightened confidence for areas of
absence of anatomical landmarks in nuclear medicine data. Co-registered SPECT-CT radiopharmaceutical uptake.
allows for differentiation between artefactual and normal uptake, and pathological
uptake. One of the biggest considerations of using low resolution or high dose CT scans
in addition to SPECT is the additional radiation dose to the patient and whether or
Research conducted by Roach et al highlighted the value of SPECT-CT in terms not the extra dose from using high-resolution CT is justified, bearing in mind the
of diagnostic accuracy and reporter confidence within clinical practice
23
. This extra clinical information that may be obtained. Table 1 illustrates radiation doses
evaluation of the impact of SPECT/CT on common areas of clinical practice, such that a patient will typically receive from SPECT, low-resolution and high-resolution
as bone scintigraphy, infection imaging (Gallium-67), Indium-111 octreotide scans, CT, and plain radiography for reference. As can be seen, the CT component adds
I-123/1-131 MIBG scans/treatment monitoring, and Tc-99m Sestamibi parathyroid a significant amount to the total dose the patient receives; this is particularly true
scans, reflected a typical nuclear medicine department workload. Overall, the for high resolution CT. It is interesting to compare plain film and high resolution CT
utilisation of SPECT-CT added extra confidence to the final diagnosis, and reporter and the dose differential. This brings into sharp focus the need to consider carefully
confidence was also increased in particular cases where anatomical landmarking whether CT or plain film imaging would give the same radiological information
would have been an issue without the CT data. The following case study and, if so, whether the lower dose alternative (plain film) would be better justified.
demonstrates the clinical value of diagnostic accuracy using SPECT-CT.
Professional responsibilities and legislative
Case Study
considerations
A 78 year old female had known multiple liver metastases from a carcinoid Depending upon local circumstances in clinical imaging departments, radiographers
tumour and Yttrium-90 therapy was being considered. An In-111 octreotide SPECT- can be referrers, practitioners and operators within the context of the Ionising Radiation
CT scan was conducted (see figure 3). As can be seen, the images demonstrate (Medical Exposure) Regulations
2
(IR(ME)R). Within nuclear medicine and with regard
liver metastases, incidental adrenal gland findings and hydronephrosis. The to radiopharmaceuticals, this is not the case. Radiopharmaceuticals are regulated
46
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IMAGING & ONCOLOGY
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2009
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