PET-CT
imaging with F-18 FDG is comparable to conventional imaging
modalities in detecting primary and metastatic disease, and
it has been used for primary staging of head and neck cancers.
The main advantage of FDG-PET-CT imaging is its ability to
detect primary and metastatic disease by a single study as
compared to a combination of imaging modalities like CT-scan
of head and neck, X-ray of chest, ultrasound of the liver
and radio-nucleotide bone scan.
It is
most useful in detecting recurrent disease in patients who
have been treated. In the post-treatment setting after surgery,
radiotherapy and chemotherapy often results in distortion
of normal anatomy. It is often difficult for conventional
imaging methods to distinguish between post therapy fibrosis
and tumour recurrence. FDG-PET imaging is more accurate in
detecting tumour recurrence with reported sensitivity and
specificity of 88% and 100% vs 25% and 75% for MRI and / or
CT imaging.
An emerging
application of FDG-PET imaging is in the monitoring of treatment
response. Reported sensitivity and specificity of FDG-PET
imaging in detecting residual cancer after therapy was 90%
and 85% respectively. The ability to detect residual cancer
after therapy obviously play an important role in the management
of patients as it helps clinicians to decide whether further
salvage therapy is required.
Another
important application of FDG-PET imaging is in the detection
of an unknown primary in patients presenting with cervical
nodal disease. FDG-PET imaging has made a major impact in
the management of these patients by detecting the site of
primary disease in 10 to 60% of cases even when conventional
imaging and clinical investigations have failed.
FDG-PET
imaging is also useful in detecting recurrent disease in patients
with well differentiated thyroid cancers where the thyroglobulin
level is rising and the Iodine-131 whole body scan is normal.
FDG-PET imaging often detects non-iodine avid lesions and
can lead to changes in management plans.
Dr Gilbert
Keng
Associate Consultant
Department of Nuclear Medicine, SGH
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