PET Scans in the Head and Neck Joseph C. Sniezek, MD FACS Head and - - PDF document

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PET Scans in the Head and Neck

Joseph C. Sniezek, MD FACS Head and Neck Surgery Tripler Army Medical Center

Diagnostic imaging

• 1. Anatomic information
• x-ray
• CT
• MRI
• Ultrasound
• 2. Physiologic/Metabolic information
• Nuclear Medicine Scan
• PET scan

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PET Scans

• Utilize Positron-Emitting

radiopharmaceuticals to map the in vivo physiology of the human body

• produces Tomographic images of

function rather than form

PET Scan for Surgeons

• Nuclear medicine scan
• Principle- tumors are

hypermetabolic, so glucose uptake high

• 8 hour fast
• 18fluorodeoxyglucose

(FDG) injected

• 1 hour wait
• Scan
• Fuse/overlay with CT

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Information from a PET scan

• 1. Pictorial information (subjective

reading) PET Dedicated PET PET/CT

Information from a PET scan

• 2. Objective numerical evaluation – standard

uptake value (SUV)

• Challenge with PET is that inflamed tissue

also takes up FDG

• Must differentiate tumor vs. inflammation
• SUV is a measure of uptake “intensity”
• SUV > 2.4 is suspicious for malignancy,
• SUV < 2.4 likely inflammatory
• Clinical background/timing important

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PET Scan Background

• Cost- $3,400
• PET/CT- $4,800
• Availability variable
• Emerging

technology

• Interesting research

tool

• Clinically useful?

When should I order a PET scan?

1. Evaluation of the primary 2. Evaluation of the N0 neck 3. Unknown primary 4. Distant mets 5. Tumor surveillance 6. Residual nodal abnormality post chemo/XRT 7. Thyroid cancer 8. PET/CT fusion

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• 1. Evaluation of the known

primary

• No advantage over CT/MRI
• Insufficient anatomic detail
• Does not change treatment plan
• No real role Arch Otolaryngol Head Neck Surg 2012;138(8)
• 2. Evaluation of the NO neck
• Can PET help me decide when to
• perate on an N0 neck?
• PET only detects tumors > 5-10 mm
• Malignant nodes > 5-10 mm can be

seen on CT or MRI or ultrasound

• Treatment plan not altered by PET

Head and Neck 2009; 31(3)

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• 3. Unknown primary
• Unknown primary represents 5-10% of cases

presenting with SCC in isolated LN

• Pt with 4 cm left node (SCC), negative exam

and panendo (1.2 cm SCC found in left tonsil) CT CT PET

(4 cm left LN) (nl oropharynx) (pos L neck and OP)

Problem- false negatives

• Pt with 2.5 cm right JD lymph node positive

for SCC on FNA

• CT oropharynx normal, PET only shows right

nodal uptake

• Panendo- 2 mm occult right tonsillar carcinoma

CT CT (neg) PET

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Unknown Primary

• Detection rate of occult primary only

25-30%

• Sensitivity of PET only 66% in unknown

primary

• Negative PET does NOT preclude need

for careful panendoscopy with directed biopsies

Eur Arch Otorhinolaryngol 2010;267(11)

• PET only detects lesions > 5-10 mm

Miller et al. Curr Onc Reports 2007; 9(2) Journal of Oncology (2009); 1-13.

• 4. Distant Metastasis
• PET much more effective in

identifying distant disease than CT

• study of 12 pts stage III/IV

SCC H&N

• PET- found distant disease

in 25% CT- 8%

Teknos et al Head Neck 2001;23

• PET 100% sens with 85%

PPV in benign vs. malig. lung lesions

J of Nucl Med 2007; 48(10) Arch Otolaryngol Head Neck Surg 2012;138(8

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• 5. Tumor Surveillance (pt follow-

up)

• Following H&N pts difficult
• physical exam affected by scarring
• radiographic changes due to XRT
• PET 82-95% accurate in differentiating

recurrent Ca from radiation changes

• CT & MRI only 45-66% accurate

J Nucl Med 2009; 50(1)

Example

• Pt 9 mo. s/p excision left FOM tumor

with pain

• Normal exam, CT with only operative

changes, PET diagnostic of recurrence

Nl CT PET PET/CT

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Timing

• Most recurrences occur within 24

months of therapy

• PET should be performed no sooner

than 12 weeks after surgery +/- chemo/XRT due to inflammation

• Timing controversial
• I order PET at 1 year post-rx or sooner

if suspicious (sens 100%, NPV 100%)

J Nucl Med 2009; 50(1)

• 6. Residual nodal

abnormalities

After chemo/XRT what do abnormal LN’s on CT mean?

• Lavertu data- does pathologic disease mean clinical failure?

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• 6. Resid. Nodal abnormal.
• 112 pts, compl resp at primary site
• PET/CT at 12 weeks post-treatment
• + PET had ND, - PET observed
• 50 pts had residual CT abnormal (41

PET -, 9 PET +)

• 7/9 PET + pts had residual disease
• NO PET - PATIENTS FAILED
• 7. Thyroid cancer
• Pts with high TG, but neg WBS difficult
• Cause- de-differentiated thyroid cancer

cells lack ability to concentrate iodine

• PET 82% sensitive in pts with negative

I-131 scans

• Higher TSH increases FDG uptake, so

TSH stimulation should be used with PET

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• 8. PET/CT
• PET/CT superior to

PET or CT alone in diagnosing recurrent H&N cancer (Univ. Pittsburgh)

• PET/CT 98%

sensitive, 92% specific (inflammation, infection, etc)

Pharynx? node

Head and Neck 2011; 33:87-94

Take-away points

• 1. Local disease follow-up- H&N PET has

PPV of only 64-90%, NPV of 97%

• 2. Negative PET in H&N is highly

reliable, positive PET is not due to high false-positivity

• 3. PET very helpful in pt f/u at 1 yr

(radiation changes vs. recurrence)

• 4. PET very good at finding distant mets
• 5. PET very helpful in thyroid disease

Head & Neck 2011; 14(Jan)

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When should I order a PET scan?

1. Evaluation of the primary 2. Evaluation of the N0 neck 3. Unknown primary 4. Distant mets 5. Tumor surveillance 6. Timing- (min 3 months post-rx) 7. Post chemo/XRT? 8. Thyroid cancer- (high TG, neg WBS)

Mahalo