(PET) and computed tomography
(CT) fusion imaging is a
rapidly evolving technique that is useful
in the staging of non-small-cell
lung cancer (NSCLC), Hodgkin's disease,
ovarian cancer, gastrointestinal
stromal tumors, gynecologic malignancies,
and breast cancer. In their article,
Rusthoven et al describe the role
of PET-CT in head and neck malignancies
and include a review of all
currently available literature. According
to the authors, PET-CT is useful
for staging head and neck carcinomas
and for target volume delineation during
radiation treatment planning.
PET-CT is quickly becoming the
standard of care for staging malignancies
at certain anatomic sites. A
study by Antoch et al compared
PET-CT with whole-body magnetic
resonance imaging (MRI). The overall
stage was correctly determined in 77%
of patients with PET-CT and in 54%
with MRI. Moreover, compared with
MRI, PET-CT had a direct effect on
disease management in 12 patients.
In a landmark study by Lardinois et
al published in the New England Journal
of Medicine, PET-CT was found
to improve the accuracy of NSCLC
staging over PET and CT alone; the
combined modality provided additional
staging information in 41% of patients.
In head and neck tumors,
PET-CT again appears to be superior
to PET alone, and probably also to
PET and CT when both are assessed
side by side for detection of tumor
invasion and staging accuracy.
Schoder et al found that PET-CT
was more accurate in depicting cancer
than was PET alone, and PET-CT findings
resulted in a change in treatment
in 12 of 68 patients, further establishing
the higher efficacy of PET-CT over
PET alone in recurrent head and neck
cancer. Therefore, PET-CT may become
a "one-stop shop" for oncologic
staging of head and neck cancers.
Advantages of PET-CT
A major advantage of PET-CT over
PET alone is the notable reduction in
scanning time. A PET scan is composed
of an emission scan, depicting
the distribution of fluorine-18 fluorodeoxyglucose
(FDG) in the body, and
a transmission scan that is used for
attenuation correction. For PET, the
transmission scan can take approximately
20 minutes, increasing the total
scanning time to approximately 50
minutes. In PET-CT, the CT data
are used for attenuation correction,
and a whole-body scan can be performed
in under 2 minutes.
An additional advantage of PETCT
is that the intrinsic hardware provides
high-quality images through
coregistration of both image datasets
in a relatively fast acquisition time.
The coregistration of datasets obtained
by different techniques (ie, PET with
CT or MRI) at different time points
may lead to inaccurate anatomic and
physiologic delineation of the tumor
with respect to normal tissues. These
inaccuracies may be caused by anatomic
changes, neck repositioning, or
head and neck swelling.
Feasibility studies have found that
the use of PET-CT for planning threedimensional
(3D) conformal radiation
therapy improves the standardization
of volume delineation compared with
CT alone.[9,10] Rusthoven et al report
that since July 2002, PET-CT fusion
imaging has been an integral
planning component for intensity-modulated
radiation therapy in patients with
head and neck cancer. Changes in the
TNM stage have ranged from 14% to
36% with PET-CT, and treatment volume
and dose have been altered in 14%
and 11% of patients, respectively.
That said, the authors do not define
the appropriate threshold by which
physiologic disease is correlated with
anatomic disease. The resolution for
clinical PET is approximately 5.0 to
7.0 mm, and without pathologic correlation
to help determine the true extent
of gross and microscopic physiologic
disease, the radiation treatment volumes
could be altered drastically. Furthermore,
partial volume and misregistration
effects can extend a portion of the
PET-defined target volume into air
spaces (ie, the larynx or trachea), which
may alter the treatment volume.
Rusthoven et al also note that PETCT
is not as sensitive in diagnosing
tumors < 2 cm in diameter and may
result in false-positive findings in inflammatory
tissue or lesions.
Institutional variability in defining
the threshold of malignant disease
with physiologic imaging can have a
profound effect on the contoured biologic
tumor volume. By raising or
lowering the threshold, the resultant
sensitivity is altered, and the volume
of contoured disease decreases or increases,
respectively. This may ultimately
result in the underdose or
overdose of the actual tumor volume.
Recently, Scarfone et al found
that the threshold of PET images was
adjusted on a case-by-case basis to adequately
visualize FDG-avid lesions
relative to the background, with the
resultant "average" threshold being approximately
50% of maximum image
intensity. They further expressed concern
about the use of PET-CT for radiation
treatment planning by pointing
out that the optimal threshold needed
to standardize the settings has yet to be
determined. For this reason, we have
resisted the urge to modify treatment
planning contours by incorporating
PET-CT in radiation treatment planning
for head and neck cancer at our
institution. Future studies confirming
gross and microscopic pathologic disease
with PET-CT will help define the
appropriate threshold settings to better
delineate target volumes.
In the multidisciplinary management
of patients with cancer, PET-CT is an
exciting and rapidly evolving technique
that is improving our ability to make
better treatment decisions. The use of
PET-CT for staging primary and recurrent
head and neck lesions is "ready for
prime time," but its application in head
and neck cancer treatment planning
should be viewed as investigational until
we can better correlate our imaging
findings with gross and microscopic
pathologic findings and resolve the issues
of variable FDG uptake by the
tumor and nodal metastases as well as
institutional threshold variability.
1. Rusthoven KE, Koshy M, Paulino AC: The
Role of PET-CT fusion in head and neck cancer.
Oncology 19:241-246, 2005.
2. Antoch G, Vogt FM, Freudenberg LS, et
al: Whole-body dual-modality PET/CT and
whole-body MRI for tumor staging in oncology.
JAMA 290:3199-3206, 2003.
3. Lardinois D, Weder W, Hany TF, et al:
Staging of non-small-cell lung cancer with integrated
positron-emission tomography and
computed tomography. N Engl J Med 348:2500-
4. Bar-Shalom R, Yefremov N, Guralnik L,
et al: Clinical performance of PET/CT in evaluation
of cancer: Additional value for diagnostic
imaging and patient management. J Nucl
Med 44:1200-1209, 2003.
5. Schoder H, Yeung HW, Gonen M, et al:
Head and neck cancer: Clinical usefulness and
accuracy of PET/CT image fusion. Radiology
6. Goerres GW, von Schulthess GK, Steinert
HC. Why most PET of lung and head-and-neck
cancer will be PET/CT. J Nucl Med 45(suppl
7. Kim EE, Lee M, Inoue T, et al: Clinical
PET: Principles and Applications, pp 44-51.
London, Springer, 2004.
8. Clarke JC: PET/CT “Cometh the hour,
cometh the machine?” Clin Radiol 59:775-776,
9. Ciernik IF, Dizendorf E, Baumert BG, et
al: Radiation treatment planning with an integrated
positron emission and computed tomography
(PET/CT): A feasibility study. Int J
Radiat Oncol Biol Phys 57:853-863, 2003.
10. Daisne J, DT, Weynant B: Impact of image
coregistration with computed tomography
(CT), magnetic resonance (MR) and positron
emission tomography with fluorodeoxyglucose
(FDG-PET) on delineation of GTV’s in oropharyngeal,
laryngeal and hypopharyngeal tumors.
Int J Radiat Oncol Biol Phys 54:15-16, 2002.
11. Scarfone C, Lavely WC, Cmelak AJ, et
al: Prospective feasibility trial of radiotherapy
target definition for head and neck cancer using
3-dimensional PET and CT imaging. J Nucl
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