Value of C-11 Methionine Whole Body PET Imaging in the Diagnosis of Skeletal Metastases

Introduction: There is an increasing
clinical interest in imaging tumors’
protein metabolism through PET
studies using radiolabeled amino acids,
and one of the most commonly used
tracer in this regard is C-11 methionine.
The latter was recently employed
successfully for diagnosis and
assessment of treatment response in
some tumors. The aim of the current
study is to assess the value of 11
C-Methionine (MET) in the diagnosis
of skeletal metastases. Patients and
methods: Over approximately 12 years
in our institute (1994-2006), 8041
patients performed static MET PET
scans for local assessment of tumor
response to carbon ion radiotherapy
(CIRT) in addition to whole body (WB)
images without attenuation correction.
Out of these patients, 254 cancer
patients had reported areas of abnormal
skeletal MET uptake on WB images.
Sixty studies were only included
because of available follow up with
conventional imaging modalities
(CIM), as the reference standard, for
final diagnosis of the bony lesions
whether metastatic or not. All suspected
skeletal areas were counted and
differentiated, according to the degree
of uptake whether low, moderate or
intense and reported as having low,
equivocal or high metastatic possibility
respectively. Results: 77 bony areas of
abnormal MET accumulation were
reported, out of them 14 were
diagnosed to be metastatic in nature
(18.2%), while the remaining 63
(81.8%) diagnosed as benign osseous
lesions. Low, equivocal or high
metastatic possibilities were
encountered in 58, 7 and 12 osseous
sites respectively. Diagnosis of
metastases was confirmed in 1 out of 58
(1.7%), 2 out of 7 (28.6%) and 11 out of
12 (91.7%) sites with low, equivocal
and intense tracer uptake respectively.
The sensitivity, specificity, positive
predictive value (PPV), negative
predictive value (NPV) and accuracy of
MET- PET- WB study in diagnosis ofosseous deposits were 78.6%, 98.4%,
91.7%, 95.4 % and 94.8% respectively
when equivocal lesions are included in
the low possibility category. These
figures were 68.4%, 98.3%, 92.9%,
90.5% and 90.9% respectively if
equivocal lesions were included in the
high possibility category of being
metastatic.
Conclusion: MET PET WB imaging is
an accurate tool in the diagnosis of
skeletal metastatic lesions in various
malignancies. Higher diagnostic
accuracy is found when only lesions
with high degree of tracer uptake are
considered metastatic.