This document discusses head and neck PET/CT scans. It provides information on: - The types of cancers that PET/CT scans are used for in the head and neck region. - The superiority of PET/CT over CT and MRI for detecting lymph node involvement, distant metastases, and unknown primary cancers. - The key applications of PET/CT including pretreatment staging, radiotherapy planning, monitoring treatment response, follow-up care, and detecting unknown primary cancers.

1. The principles of head and neck
PET/CT scan
Tehran University of Medical Sciences
Shariati Hospital
Nuclear Medicine Department
Dr. Mustafa Al-Thabhawee

2. The term head and neck cancer (HNC) generally encompasses malignant neoplasms of soft
tissue origin of the oral cavity, lips, nasal cavity, paranasal sinuses, pharynx, larynx and
salivary glands, as well as sarcomas arising in this region.
The skin is sometimes included as well. About 95% are squamous cell carcinomas (or
variants) arising from the mucosa or adenocarcinomas from the associated secretory
glands. Infection by the human papillomavirus is recognized as an important predisposing
condition for the development of squamous cell carcinomas of the head and neck.
Positron emission tomography (PET) imaging with the radiolabelled glucose analogue 2-
deoxy-2-[18F]fluoro-d-glucose ([18F]FDG) plays an increasingly important role in the
pretreatment staging, radiotherapy planning, treatment response assessment and post-
therapy follow-up in various HNSCCs. [18F]FDG PET/CT is superior to contrast-enhanced
computed tomography (CT) and magnetic resonance imaging (MRI) in the detection of
carcinomas of unknown primary (CUP), of cervical lymph node involvement and in the
identification of distant metastases.

3. Q. What are the factors that determine the initial treatment?
The factors that determine the initial treatment are those:
1. Related to tumor characteristics (size, location, histology and nodal and metastatic
involvement).
2. The patient (age and general condition) and the factors depending on availability.
Most patients present with complicated locally advanced disease requiring multidisciplinary
treatment plans based on variable combinations of surgery, radiation therapy and
chemotherapy.

4. Q. What are the indications to perform PET/CT in head and neck
tumors?
1. Pretreatment Staging
Numerous of reports on initial staging indicate that the sensitivity of PET/CT is equivalent to or
superior to that of MRI and CT. In comparison to morphological imaging methods (CT or MRI),
PET/CT is particularly advantageous in allowing:
 assessment of neck lymph nodes.
 potential distant metastases.
 synchronous second primaries in a single examination (see Figs. 19.1 and 19.2). The
sensitivity and specificity of [18F]FDG PET/CT in staging nodal disease of about 79–85% and
84–86%, respectively, whereas sensitivity and specificity of conventional diagnostic tests
(MRI, CT and ultrasounds) were 75% and 79%, respectively

5. Approximately 4–15.4% of patients with HNSCC have distant metastases at initial presentation.
The most common sites of metastasis include the lung, bone and abdomen.
Whole-body [18F]FDG PET/CT is more accurate than conventional imaging for detection of
metastatic foci.
In addition, [18F]FDG PET/CT detects distant metastases or a second primary tumor in up to 15%
patients with squamous cell carcinoma, which can significantly alter treatment plans.
In 2017, the National Comprehensive Center Network updated the clinical practice guidelines
for PET/CT imaging of head and neck cancer and suggested the use of PET/CT for initial staging
of oral cavity, oropharyngeal, hypopharyngeal, glottic and supraglottic cancers for stage III–IV
disease, as well as mucosal melanoma and nasopharyngeal Carcinoma.

8. Q. What is the Synchronous Lesions?
The most common areas for second primary tumors are the lung and aero digestive tract .The overall incidence of
coincidental secondary primary tumors is 5 to 10%. PET has an accuracy of 80% for coincidental lung lesions. PET/CT
detected 84% of synchronous primaries, and therapy was changed in 80% of patients due to detection of synchronous
primaries. In another study, PET/CT was superior to pan-endoscopy for the detection of synchronous primaries, and the
authors suggest that the extent of endoscopy can be reduced to the area of the primary tumor if PET/CT is negative.

9. Staging, Grading, & Classification
• General
○ Most sites of H&N use same AJCC (2010) TNM staging system, including lip, oral cavity, oropharynx, hypopharynx, larynx,
and salivary glands
• Tumor (some site specific criteria for advanced staging)
○ T1: ≤ 2 cm
○ T2: > 2 cm and ≤ 4 cm
○ T3: > 4 cm
○ T4: Moderately advanced local disease
• Nodes (same for most H&N sites)
○ NX: Regional LNs cannot be assessed
○ N0: No regional LN metastases
○ N1: Single ipsilateral LN ≤ 3cm
○ N2
– N2a: Single ipsilateral LNs, 3-6 cm in greatest dimension.
– N2b: Multiple ipsilateral LNs, ≤ 6 cm in greatest dimension.
– N2c: Bilateral or contralateral LNs, ≤ 6cm in greatest Dimension.
○ N3: LNs > 6 cm in greatest dimension.

10. Although PET/CT is more accurate than CT or MRI for nodal metastases. it does not
detect very small metastatic deposits ( < 5 mm). Neck dissection in patients with a
negative PET may be performed on pretest likelihood of metastatic disease (e.g.,
based on T -stage and histopathologic features). In patients with T4 disease, false-
negative results are more likely and PET is less helpful. PET is more helpful in patients
with 11 to T3 disease. The use of PET in this population can reduce the probability of
occult neck metastases to less than 15%. In addition, false-positive results are not
infrequent and are more common in the contralateral neck side, and in clinical NO
necks. Pathologic confirmation should be considered for PET positive nodes. PET/CT
may have the most potential value where the probability of occult nodal metastases
is higher (e.g., in patients with oral or oropharyngeal cancer). The sensitivity of PET in
this setting is variable. ranging from 33 to 67%.
The role of PET in nodal metastases

11. 2. Radiotherapy Planning
The importance of PET/CT in the planning of radiotherapy in HNSSC patients has been
extensively demonstrated. [18F] FDG PET/CT defined tumor volume more definitively than
diagnostic CT without contrast medium. [18F]FDG PET/CT modified staging and radio-
therapeutic planning in up to one-third of untreated HNSSC patients.
Abramyuk et al. compared the staging modifications determined by [18F]FDG PET/CT in 102
patients with untreated primary HNSSC. [18F]FDG PET/CT imaging led to modification in RT
planning in 14 of 102 patients (13.7%).
As such, [18F]FDG PET/CT improved selection of candidates for curative and palliative RT.

12. Potential applications of PET in radiotherapy planning are as following:
1. Co-registration of PET and treatment planning by CT.
2. Detection of additional/distant disease by PET.
3. Delineation of radiation therapy target volume. Gross tumor volume (GIV) assessment by PET is
closer to the surgical specimen than CT or MRI. although all imaging modalities overestimate tumor
extension.
PET/CT has several potential advantages: reduction in size of the GTV, reduction of inter observer
variability in GTV delineation, identifying parts of the GTV potentially requiring additional radiation dose,
and identifying tumor extension missed by CT or MRI.
The GTV identified by PET is dependent on the segmentation method used (e.g.. visual interpretation
results in higher volumes than semiautomatic methods). All methods show a smaller tumor
volume on PET/CT compared to only CT.
Also, PET/CT often suggests tumor extension outside the CT-based tumor volume.

13. In radiotherapy planning,
[18F]FDG PET/CT results in
significant reduction of
metabolic gross tumor
volume (GTV) with respect
to GTV planning with CT.

14. Radiation effect
Diffuse FDG uptake in the radiation field is usually
secondary to Post-radiation inflammation. Increased
laryngeal or oropharyngeal uptake can be noted for
prolonged periods after chemoradiotherapy. Typically,
this uptake is diffuse and of mild to moderate intensity.
Focal, asymmetric uptake greater than surrounding
tissues, particularly muscle, is suspicious for residual or
recurrent disease as long as it does not fuse to
anatomic structures.

15. 3. Monitoring of Response to Therapy
Chemoradiation has been used for the treatment of locoregionally advanced HNSCC. It has been
accepted as a part of the definitive treatment after surgery. PET/CT has significant advantages
for treatment response assessment as it is a functional imaging approach, and does not rely on
morphological changes.
A 63-year-old man with right tonsil carcinoma
(T3N0M0) treated with neoadjuvant
chemoradiotherapy. Transaxial slices of CT,
[18F]FDG PET and fused PET/CT images prior to
treatment (top row) show intense
hypermetabolism in right tonsil. Transaxial
slices of CT, [18F]FDG PET and fused PET/CT
images 3 months after treatment (bottom row)
show disappearance of tumor lesion
suggesting complete response to treatment.

16. In general,
 Focal and asymmetric [18F]FDG uptake with intensity greater than in surrounding
normal tissues (in particular, muscle) and blood vessels should be considered
suggestive of residual disease.
 Other hand, diffuse (non-focal) [18F]FDG uptake within the radiation field is usually
an indicator of post-radiation inflammation.
The authors support the use of PET/CT 12 weeks post-treatment for the assessment of
residual or recurrent disease, whereas the potential clinical utility of PET for early
response assessment (PET interim) during chemo-radiotherapy has not been explored
systematically.

17. 4. Follow-Up
The need and frequency of post-treatment imaging assessment for patients treated for HNSCC
are still highly controversial. It is unclear whether patients with distant relapse, but without
symptoms, benefit from early detection of disease.
Early detection of locoregional recurrence may potentially improve survival by facilitating timely
salvage treatment.
Overall sensitivity and negative predictive value (NPV) for locoregional recurrence were higher
using PET/CT (92.5% and 94.8%, respectively) than conventional imaging (55% and 76.9%,
respectively).
They concluded that, for routine surveillance, the initial PET scan should be performed within 6
months after completion of treatment and the proper timing of next routine PET scan for
subclinical patient with initial negative PET result might be 1 year after initial PET scan.

18. 5. Prognosis:
Pretreatment tumor FDG uptake Is an independent prognostic factor
in a meta-analysis, low FDG uptake before treatment is correlated
with better disease-free survival, overall survival and local Control.

19. 6. Cervical Carcinoma of Unknown Origin
An unknown primary tumor in the neck is diagnosed when a patient presents with a
neck metastasis, but no primary tumor is found.
The treatment of an unknown primary tumor can consist of:
 Neck dissections.
 Tonsillectomies.
 Radiation therapy for all mucosal sites and both sides of the neck.
According to several studies, [18F]FDG PET/CT is very helpful in localization of primary
tumor. 18F FDG PET/CT showed higher sensitivity (69%) for detection of occult primary
tumors than did CT (16%) (P < 0.001) or combined CT and MRI (41%, P = 0.039) in
patients with cervical metastasis from an unknown primary tumor.

20. A 70-year-old man with metastatic neck
lymph node of unknown primary tumor.
Coronal, sagittal and Transaxial slices of
CT, [18F]FDG PET and fused PET/CT
images show hypermetabolism in lymph
node left neck area (thin arrow) and
hypermetabolism in left tonsil (thick
arrow).
Surgical histopathology demonstrated a
primary tonsil tumor.

21. Key Learning Points
• The performance of [18F]FDG PET/CT is equivalent to or superior to that of CT and MRI for
initial pretreatment staging of patients with head and neck cancers.
• Distant metastatic sites in patients with head and neck cancers are detected by [18F]FDG
PET/CT with greater sensitivity and specificity than conventional imaging with either CT or MRI.
• NCCN guidelines recommend [18F]FDG PET/CT for initial staging of oral cavity, oropharyngeal,
hypopharyngeal, glottic and supraglottic cancers for stage III–IV disease.
• In a substantial fraction of patients with head and neck cancers, integration of [18F]FDG PET/CT
in the pretreatment imaging protocol planning results in modification of radiotherapy planning.
• [18F]FDG PET/CT has greater sensitivity and specificity than either CT or MRI for assessing
response to therapy in patients with head and neck cancers submitted to chemotherapy and/or
radiotherapy.
• During post-therapy follow-up of patients treated for head and neck cancer, [18F]FDG PET/CT
has greater sensitivity and negative predictive value than conventional imaging.
• [18F]FDG PET/CT has greater sensitivity than either CT or combined CT and MRI for detecting
occult primary tumors in the head and neck region.

22. Contraindications (Relative)
1. Pregnancy
For any diagnostic procedure in a female patient known or suspected to be pregnant, a
clinical decision is necessary in which the benefits are weighed against the possible harm.
The International Commission on Radiological Protection (ICRP) reports that for an adult
patient, the administration of 259 MBq (7 mCi) of [18F]FDG results in an absorbed radiation
dose of 4.7 mGy to the non-gravid uterus (i.e.1.8 × 10–2 mGy/MBq).
A pregnancy test may help with the decision, provided the 10-day post-ovulation blackout is
Understood.

23. 2. Breast-Feeding
The ICRP does not recommend interruption of breast-feeding after [18F]FDG administration,
since little [18F]FDG is excreted in the milk. However, as the lactating breast accumulates
[18F]FDG, it is suggested that contact between mother and child be limited for 12 h after
injection of [18F]FDG in order to reduce the radiation dose that the infant receives from
external exposure to radiation emitted by the mother.
3. Lack of Cooperation
The lack of cooperation or the inability to cooperate with the procedure may be relative
contraindication.

24. Patient Preparation
The main purpose of patient preparation is to reduce tracer uptake in normal tissue (kidneys, bladder,
skeletal muscle, myocardium, brown fat) while maintaining and optimizing tracer uptake in the target
structures (tumor tissue) while at the same time keeping patient radiation exposure levels as low as
reasonably possible (ALARA).
1. Before reporting to the Nuclear Medicine Centre, nondiabetic patients should not consume any food,
simple carbohydrates or liquids other than plain (un-flavored) water for at least 4 h prior to the start of
the [18F]FDG PET/CT study. Type I and insulin-dependent type II diabetic patients should not have insulin
injections for at least 4 h before [18F]FDG injection, and they should be made to achieve normal glycemic
values prior to the study. Type II non-insulin-dependent diabetic patients should continue to take oral
medication to control their blood sugar level.
2. The blood glucose level should be checked before [18F] FDG administration. Tumor uptake of [18F]FDG is
reduced in hyperglycemic states. Most institutions reschedule the patient if the blood glucose level is
greater than 150–200 mg/dL. Reducing the serum glucose level by administering insulin can be
considered, but the administration of [18F]FDG should be delayed 4 h after insulin administration.
3. When a diagnostic CT scan with intravenous contrast agent enhancement is to be performed as part of
the [18F] FDG PET/CT study, indications, contraindications and restrictions have to be assessed by a
qualified physician.
4. Medication that interacts with intravenous contrast agent (e.g. metformin for the treatment of diabetes)
and relevant medical history (e.g. compromised renal function, adverse reactions or claustrophobia)

25. Radiopharmaceutical
Activity: The minimum recommended administered [18F] FDG activity and PET acquisition
duration for each bed position must be adjusted. Therefore, one may decide to apply a higher
activity and reduce the duration of the study or, preferably, to use a reduced activity and
increase the study duration, thereby keeping ALARA principles in mind as well.
There are different methods for determining the minimum [18F]FDG administered dose in adults.
One specification is 3.7 MBq/kg (0.1 mCi/kg), while other specifications include the time per bed
position and patient weight.
Uptake period: for [18F]FDG: The recommended interval between [18F]FDG administration and
the start of acquisition is 60 min.
Following the injection, it is important for the patient to rest quietly during this period, as
excessive motion may result in muscle uptake; talking should be avoided to minimize vocal cord
activity.
Patients may go to the toilet while waiting, preferably more than 30 min after injection. Patients
should empty their bladder 5 min before the start of the [18F]FDG PET/CT study.

26. Acquisition
1. PET/CT imaging from the skull base to proximal thigh: the arms should be elevated over the
head if the patient can tolerate this position. The CT scan is used for attenuation correction of
the PET images as well as for anatomic localization. The head and neck region is typically
included in routine skull base-to-proximal thigh PET study.
The strategy is:
• CT topogram: 120 kV; 10 mA
• Low-dose CT scan: 140 kV; 80 or 50 mA
• PET acquisition from the skull base to proximal thigh (time per bed between 1.5 and 3 min).
2. PET/CT imaging of the neck: the arms should be down to eliminate streak artefacts from the
humerus. To improve the spatial resolution, a smaller field of view can be used.
The strategy is:
• CT topogram: 120 kV; 10 mA
• Intravenous contrast-enhanced diagnostic CT scan
• Head and neck PET acquisition (with 30 s of delay) If the PET/CT data are used for radiotherapy
planning, the PET/CT imaging of the neck should be performed in the position used for
radiotherapy treatment, employing the same dedicated positioning devices (e.g. the same
radiotherapy table top, laser alignment, immobilization mask and measures).

27. Physiological [18F]FDG Distribution
1. Physiologic uptake of [18F]FDG can be seen to some extent in every viable tissue, including the
tonsils and at the base of the tongue due to physiological accumulation in the lymphatic tissue
of Waldeyer’s ring. Non-pathological hypermetabolism can be identified in salivary glands,
muscles of the floor of the mouth and ocular extrinsic, cervical or masticatory muscle
A 82-year-old man in surveillance after
treatment of T3N1M0 carcinoma of oral
cavity. Coronal and transaxial slices of CT,
[18F]FDG PET and fused PET/CT images
show an intense hypermetabolism in
vestibular/gingival mucosa due to
inflammatory processes caused by bad
oral hygiene (thin arrow). There is also
bilateral uptake in digastric musculature
that must be considered as physiological

28. 2. Uptake in cervicothoracic brown fat is observed more often in young patients and -
when the ambient temperature is low. Brown fat uptake is often identified by matching
regions of fat attenuation on CT with the PET/CT fused images.
Volumetric display (MIP),
coronal and transaxial slices of
CT, [18F]FDG PET and fused
CT/PET images showing a very
intense and symmetrical
[18F]FDG uptake in
cervicothoracic brown fat.
Hypermetabolic areas are
located in low-density areas
visualized in CT, corresponding
to fat tissue.

29. 3. Bilateral uptake in vocal cords can be observed when the patient speaks during the uptake
interval after [18F]FDG administration, with greater uptake of the healthy cord as a compensation
for a contralateral recurrent nerve paralysis.
4. The lymph node anatomy of the head and neck is complex and must be well known to
correctly interpret the findings of PET/CT.
5. Increased uptake of [18F]FDG can be seen in granulation tissue (e.g. healing wounds),
infections and other inflammatory processes as well as in benign salivary gland tumors, such as
the pleomorphic adenoma and Warthin’s tumor, which may present high uptake of [18F]FDG.
A detailed description of pitfalls and situations that can lead to false-positive (benign processes
that can show [18F]FDG uptake) or false-negative [18F] FDG PET/CT interpretation has been
published.

30. Key Learning Points
• Display of images from an [18F]FDG PET/CT scan in patients with head and neck cancers follows
the general format and modalities as for other regions of the body.
• Particular attention should be paid to evaluation of the non-CT attenuation-corrected images.
• Physiological uptake of [18F]FDG with variable intensity can be observed in normal structures of
the head and neck including the lymphatic Waldeyer’s ring; major salivary glands; muscles of the
floor of the mouth; ocular extrinsic, cervical or masticatory muscles; brown fat; and vocal cords.
• Good knowledge of the complex anatomy of lymph nodes of the head and neck is mandatory
to correctly interpret the [18F]FDG PET/CT scan.
• The possibility of increased [18F]FDG uptake in inflamed/healing tissues (such as early after
surgery or radiotherapy) as well as in some benign tumors must adequately be taken into
account when interpreting an [18F]FDG PET/CT scan of the head and neck.
• [18F]FDG accumulation at tumor sites must be adequately correlated with anatomic
abnormalities observed in the CT component of the PET/CT scan.

31. Normal uptake (sagittal). On sagittal images, there is normally an inverted C' shape
composed of the mylohyoid muscles and sublingual glands, soft palate, and
tonsils).
These are the most common areas of normal uptake.

33. Soft palate (axial)
The soft palate can appear as a prominent focus of activity on axial
images. Soft palate uptake is more prominent in males.

34. Tonsils (coronal)
Normal uptake in the palatine and lingual tonsils) forms two
vertical linear bands of uptake on coronal images .This may be
prominent In cold/temperate climates and is also prominent In
children.
a) Asymmetric physiologic tonsil uptake can be difficult to
differentiate from tonsillar carcinoma.
ln one study, 23 a ratio of SUVmax between the tonsils (with a
cutoff of 1.48) was effective in differentiating tonsillar cancer
from asymmetric physiologic uptake.
b) There is less uptake with increasing age in the
palatine tonsils. Salivary glands.
Salivary gland uptake is more variable than tonsillar uptake.
Salivary gland uptake, if seen, is usually less than tonsillar uptake.

35. a) There is less uptake with increasing
age ln the sublingual glands.
b) The submandibular glands are in
close proximity to submandibular
nodes and submandibular nodal
uptake can be difficult to distinguish
from normal glandular uptake even
with PET/CT.

36. Nasopharyngeal uptake:
Nasopharyngeal uptake is sometimes seen as a normal variant although larger degrees of uptake could be secondary to
inflammation or tumor. Uptake in the lateral pharyngeal recess can be symmetric or asymmetric.
a) Asymmetric uptake. Asymmetric uptake in the lateral pharyngeal recess, cervical nodal uptake, and asymmetric wall
thickening In the lateral pharyngeal recess on CT are associated with nasopharyngeal carcinoma.
• However, in patient populations where nasopharyngeal carcinoma is less frequent. asymmetric uptake in the lateral
pharyngeal recesses is often Inflammatory.
b) An SUV cutoff of< 3.9 and a lateral pharyngeal recess-to-palatine tonsil uptake ratio of< 1.5 are helpful in
differentiating benign from malignant lateral pharyngeal recess uptake.
c) Uptake in the midline roof the nasopharynx could be secondary to uptake in adenoidal tissue or nasopharyngeal
carcinoma.
In one study, 0an SUV level of less than 4.61 and a midline roof-to-palatine tonsil ratio of< 1.14 were helpful in
differentiation. Although there was stilt overlap between neoplastic and non-neoplastic uptake levels. Additional findings
were necessary to increase the accuracy of PET. For example. associated increased FDG uptake in Waldeyer's ring and the
salivary glands occurred in benign but not malignant lesions. Symmetric uptake in the lateral pharyngeal regions was
associated with benign etiologies.

37. Presentation
• Most common signs/symptoms
○ May present with pain associated with primary mass or neck mass.
○ Other symptoms may include mouth sores, sore throat, dysphagia, otalgia, odynophagia, voice changes
Treatment
• Radiation therapy ― chemotherapy
• Radical, modified radical, or selective neck dissection.
○ Radical neck dissection: Excision of levels I-V LNs, SCM, internal jugular vein and cranial
nerve XI.
○ Modified radical neck dissection: Excision of levels I-V LNs and cranial nerve XI
○ Selective neck dissection: Excision of selective nodal groups.

38. (Left) Lateral graphic of the neck depicts nodal levels. I: Submental-submandibular; II: High jugular; III:
Mid jugular; IV: Low jugular; VA and VB: High and low spinal accessory; and VI: Anterior cervical.
(Right) Axial fused F-18 FDG PET/CT shows primary squamous cell carcinoma near the base of tongue
ſt. Some primary lesions are too small to be detected on F-18 FDG PET/CT.

43. Pearls/Pitfalls
1. Knowledge of the common sites and incidence of cervical metastases for different primary tumors is helpful in the
interpretation of PET Scans.
a) Oral cavity tumors have high incidence of metastases despite being clinically node negative.
b) Laryngeal tumors have a low incidence of metastases even in advanced stages of disease.
c) Supraglottic larynx tumors often spread to nodes.
d) Nasopharyngeal tumors often spread to nodes bilaterally and to the posterior triangle.
2. The most common site of reactive lymphadenopathy is the jugulodigastric node. Reactive nodes are often enlarged and
less intense than the primary and nodal Metastases.
3. SUV volume: It is helpful to include the abdomen and pelvis in the scan volume because of the possibility of
coincidental tumors and distant metastases.
4.Bone invasion: ln a meta-analysis,32 PET/CT had a mean sensitivity of 83% and a mean specificity of 90% for the
detection of mandibular invasion by head and neck cancers, compared to 96 and 66%, respectively, for SPECT. In patients
with oral cancer. PET does not improve identification of bone infiltration compared to CT.
5. SUV: The use of size-based SW cutoffs may be helpful for nodal staging. In one study, SUV cutoffs of 1.9. 2.5, and 3.0 for
lymph nodes< 10mm,10 to 15mm,and>15mm yielded a 79% sensitivity and 99% specificity for nodal staging. 34 The use
of the ratio of nodal/ li~ SUVmax is helpful in correcting for inter scanner variability. In one report, 35 a nodal/liver ratio
of ~ 0.90 yielded a sensitivity of 74% and specificity of93%.
6. Hardware artifact: Non-removable metallic dental implants can generate artifacts adjacent to dental implants that
mimic FDG uptake on attenuation-corrected images.

44. PET has limitations in assessing response to postoperative adjuvant chemoradiotherapy.
a) Postsurgical inf1unmatory reactions can cause false positive results and therefore render subsequent
response assessment inaccurate.
b) Microscopic residual disease cannot be Detected.
2 . Timing: As in all settings, there should be substantial time interval between radiotherapy and PET
imaging. Typically false-negative results are more commonly seen if imaging is performed early after
radiation. NCCN guidelines t suggest a minimum delay of 12 weeks after treatment In a systematic review,
sensitivity was greater fur scans performed 10 weeks or more after therapy. In a met analysis, l9 specificity
was greater for scans performed more than 12 weeks after radiotherapy with or without chemotherapy. If
post radiotherapy neck dissection is being considered, PET may be more valuable if it can be accurately
performed earlier after therapy (within 12 weeks), as fibrosis can increase the technical difficulty and
morbidity of delayed neck dissection.
3. Visual grading criteria. such as the Deauville's criteria used for lymphoma or similar criteria are also
effective in therapy response assessment in patients with head and neck cancer.
4. Osteoradionecrosis can cause false-positive results. As mean and maximum SUVs can overlap between
patients with osteoradionecrosis and tumor recurrence, the CT findings may be more reliable. A solid or
cystic mass is associated with tumor recurrence. while bony sclerosis is associated with osteoradionecrosis.
Dual time point PET may also be helpful, as the SUV may decrease over time in osteoradionecrosis.

45. Comparison with Other Modalities
1. Other radionuclides. PET is more sensitive than sestamibi, tetrofosmin,
or thallium. Specificity is comparable. However, sestamibi or tetrofosmin
combined with CT is comparable to PET.

46. 2. MRI

47. 1. Parotid lesions:
PET cannot distinguish between benign and malignant parotid tumors Warthin's tumors and pleomorphic adenomas can
have FDG uptake. High-grade salivary gland tumors tend to have more uptake than lower grade tumors, but there is
substantial overlap. In addition. some malignant parotid lesions, such as adenoid cystic carcinoma, low-grade
mucoepidermoid carcinoma. and necrotic squamous cell carcinoma can have minimal. FDG uptake. so ln a meta-analysis,
the pooled risk of malignancy of focal parotid incidental uptake was 9.6% in all detected lesions. However, in patients with
head and neck cancer/melanoma, lymphoma. or FDG-avid cervical lymph nodes. there are higher odds that the focal
parotid uptake represents metastases. PET and PET/CT may be superior to CT for staging patients with known salivary gland
malignancies.

48. Pleomorphic sarcoma. A 51-year-old male with
biopsy-proven pleomorphic sarcoma of the right
parotid gland.
FDG PET/CT demonstrated an FDG avid lesion in
the right parotid gland (a,c), corresponding to a 12
x 10 mm Soft tissue density on the CT image (b),
with moderate enhancement on contrast-
enhanced CT (d).

49. 2. Cystic neck masses:
PET/CT may not be accurate in identifying malignancy
in adults with cystic neck masses.

50. PET/CT
PET /CT is of particular value in head and neck evaluations given the complex anatomy and
relative lack of anatomic landmarks on PET.
1. The use of PET/CT compared to PET alone will decrease fraction of equivocal lesions by 53%,
greatly improve lesion localization, slightly improve accuracy, and change management in 18%
of cases.
2. Particular attention must be paid to the possibility of mislocalization on PET/CT studies due to
movement of the head between the CT
and PET studies.
3. If PET /CT or fusion with CT or MRI is not available, potential anatomic landmarks that can be
used to aid in localization include the tonsils, palate, tongue, floor of mouth, salivary glands,
mandible, and cervical spine.

51. PET Image Reconstruction
• The PET emission data must be corrected for several factors before
further processing.
• The reconstructed voxel size should be 3–4 mm in any direction
through selection of adequate matrix size and zoom factors.
• The PET emission data should be reconstructed both with and
without attenuation correction in order to identify artefacts in the CT
attenuation-corrected images due to highly attenuating materials.
• The PET emission data can be reconstructed in either the 2D mode or
the 3D mode, using suitable procedures.
• Current reconstruction methods are based on iterative approaches.
• CT image reconstruction follows standard protocols commonly
employed for routine clinical imaging.

52. Data Interpretation and Reporting
1. Fusion images must be evaluated using an SUV scale in the axial,
coronal and sagittal planes as well as maximum intensity projection
(MIP) images for review in the 3D cine mode.
2. [18F]FDG PET images with and without attenuation correction should
be available for review.
3. Quantitative information with respect to size and [18F] FDG uptake
(SUV) can be retrieved.
4. Image data should be stored on an approved PACS system and in
DICOM format.

53. Interpretation Criteria
1. Increased uptake of [18F]FDG can be seen in granulation tissue (e.g. healing wounds), infections and other
inflammatory processes as well as in benign salivary gland tumors, such as the pleomorphic adenoma and
Warthin’s tumor, which may present high uptake of [18F]FDG. A detailed description of pitfalls and situations
that can lead to false-positive (benign processes that can show [18F]FDG uptake) or false negative [18F] FDG
PET/CT interpretation has been published.
2. In neoplastic processes, tracer accumulation in anatomic abnormalities seen on CT scan or other imaging
may be particularly significant. When appropriate, the report should correlate PET/CT findings with those of
other diagnostic tests. These tests should be reinterpreted in the context of all available data imaging and
clinical data.
3. For response assessment, the images should be viewed over the same dynamic grey scale or color scale
range. In clinical trials, criteria for visual analysis should be defined a priori within the study protocol.
4. SUV (normalized to body weight) measurement is widely used in clinical studies in addition to visual
assessments. SUV normalized to lean body mass (LBM) is a recommended quantitative measure of [18F]FDG
uptake for response assessment studies, when large changes in body weight may occur during the course of
the treatment.

54. 5. Although there are no conclusive data on the optimum interval between chemotherapy and
[18F]FDG PET/CT, an interval of at least 10 days between the last treatment and the [18F]FDG
PET/CT examination is generally considered adequate for measurement of response [39]. This is
because of the balance between any possible effects on tumor metabolism (such as
macrophage impairment) and systemic effects (such as bone marrow activation following bone
marrow depression, which may or may not be caused by growth factors). If an interval of 10
days is not possible, [18F]FDG PET/CT should be delayed as long as possible after the previous
chemotherapy administration (i.e. until as close as possible to the next treatment cycle).
6. It is assumed that the side effects of radiotherapy are longer-lasting; investigations of patients
with head and neck carcinoma treated with radiation have shown that radiation-induced
inflammation can be seen on the [18F] FDG PET/CT images for 2–3 months after the end of
treatment . Waiting 2 or 3 months following completion of radiation therapy before obtaining a
PET/ CT scan is clinically appropriate, as patients rarely develop clinical problems in the first 3
months after Treatment.