PET CT

1. PET-CT FOR
HEAD AND NECK CANCER
CHANDINI RAVIKUMAR- PG III

2. CONTENTS
 Introduction
 FDG-PET CT for Head and Neck Cancer (HNC)
 Working mechanism
 Indications
 PET-CT Operation
 PET Radiotracers
 Patient preparation protocol
 Limitations

3. INTRODUCTION
 Positron emission tomography-computed tomography (PET-CT) is a radiographic technique used to diagnose,
stage, and survey hypermetabolic tissue, primarily cancer.
 PET is used primarily to assess physiology, while CT is used primarily to assess anatomy. Combining these two
methods may improve outcomes, such as survival or selecting the least invasive treatment method.
 PET-CT requires specific patient preparation and understanding of potential false positive and false negative test
results depending on whether PET-CT is used for diagnosing, initial staging, or post-treatment staging of
different head and neck cancer subtypes.
REF: Eyassu E, Young M. Nuclear Medicine PET/CT Head and Neck Cancer Assessment, Protocols, And Interpretation.
StatPearls [Internet]

4. FDG-PET CT FOR HEAD AND NECK CANCER (HNC)
 PET radiotracer imaging with labeled glucose analogue [18F]-fluorodeoxyglucose (FDG) is increasingly being
used in oncology imaging, for its usefulness in detecting and staging cancer and metastatic disease.
 Cancer cells have increased glucose utilization and FDG PET/CT is used to investigate the increased FDG
metabolism of malignant cells compared with non-malignant cells.
 For patients, the radiation burden of FDG PET/CT scan, which includes the base of skull to the pubic symphysis,
is approximately 17 mSv, or roughly that of two conventional CT scans, encompassing the chest, abdomen and
pelvis.
REF: Wai Lup Wong, Vincent Batty. Role of PET/CT in maxillo-facial surgery. British Journal of Oral and Maxillofacial Surgery,
47 (2009) 259–267.

5.  INDICATIONS OF PET-CT
 TNM Staging
 Identification of Carcinomas of unknown primary
 Monitors response to treatment
 Differentiates post-treatment changes from residual and recurrent
disease
 Radiation treatment planning
REF: Akram Al-Ibraheem. Clinical Applications of FDG PET & PET/CT in Head & Neck Cancer. Journal of Oncology, 2009.

6. WORKING MECHANISM
PET/CT- combination of a PET scanner and a CT scanner in one machine. The patient initially has a CT scan that
takes under a minute followed by a PET scan within the same scanning machine or gantry. The duration of the PET
depends largely on the radiotracer injected. Different radiotracers require different amounts of time to acquire
adequate data. For FDG it takes approximately 20 min for a scan that includes the base of the skull to the mid-thighs.
REF: Wai Lup Wong, Vincent
Batty. Role of PET/CT in
maxillo-facial surgery. British
Journal of Oral and
Maxillofacial Surgery, 47
(2009) 259–267.

7. WORKING MECHANISM
REF: Wai Lup Wong, Vincent Batty. Role of PET/CT in maxillo-facial surgery. British Journal of Oral and Maxillofacial
Surgery, 47 (2009) 259–267.

8.  PET-CT OPERATION: FLOWCHART
REF: Adam et al. PET/CT scanner instrumentation, challenges, and solutions. Radiol Clin N Am 42 (2004) 1017 – 1032

9. PET RADIOTRACERS
REF: Rosa Fonti et al. PET/CT in Radiation Oncology. Seminars in Oncology. 2019.

10.  PHYSIOLOGY AND STANDARD UPTAKE VALUE (SUV)
 18-FDG can be injected into patients with no adverse biological side effects
 18-FDG undergoes normal cell membrane transport.
 Normal tissues that conduct cell membrane transport of 18-FDG at high rates include: left ventricular
myocardium, brain, gastrointestinal tract mucosa, and kidney tubules. In addition, brown fat, skeletal muscle,
and breast ducts undergoing normal physiologic activity can also concentrate 18-FDG.
 If other tissue takes up 18-FDG- the tissue is undergoing a pathologic process, such as benign or malignant
tumor growth, infection (e.g., abscess), or another type of inflammation (e.g., arterial wall atherosclerosis).
REF: Eyassu E, Young M. Nuclear Medicine PET/CT Head and Neck Cancer Assessment, Protocols, And Interpretation.
StatPearls [Internet]

11.  PHYSIOLOGY AND STANDARD UPTAKE VALUE (SUV)
 The degree of 18-FDG cellular uptake can be quantified and assigned a standard uptake value (SUV) value.
 Calculated by computer software based on values (body mass, 18-F dose, dose-to-scan time) recorded in the
software at the time of the scan.
 SUVs vary due to scanner parameter calibrations, partial volume effects (i.e., SUV becomes less accurate with
smaller lesions), and patients' rate of glucose metabolism (which depends on many factors such as blood
glucose level).
 Many clinical studies performed with 18-FDG pre-defined 2.5 as the critical threshold; benign if its average
SUV was below this value and malignant if its average SUV was above this value.
 This strategy is based on the assumption that background tissue activity always has an average SUV below 2.5.
REF: Eyassu E, Young M. Nuclear Medicine PET/CT Head and Neck Cancer Assessment, Protocols, And Interpretation.
StatPearls [Internet]

12.  FDG PET/CT VERSUS CONTRAST CT AND MRI
Axial CT (A) and PET CT
fused images (B) for staging
of a 71-year-old man with
left gingival cancer. Dental
hardware prevents
detailed examination on
CT. PET images show a
clear focal area of tracer
uptake to suggest tumor
involvement
 In the oral cavity, FDG PET/CT is superior to CT or MRI for primary tumor detection with a sensitivity of
96.3% compared with 77.8% for CT and 85.2% for MRI.
REF: David Q. Wan. Advances in Functional Imaging in the Assessment of Head and Neck Cancer. Oral Maxillofacial Surg Clin N Am 31 (2019) 627–635.

13.  FDG PET/CT VERSUS ONLY PET
 18F-FDG PET imaging is a very sensitive and valuable imaging tool in
evaluation head and neck cancer.
 The main drawback of 18F-FDG PET alone is the limitation with respect to
lesion localization.
 However, the advent of PET/CT now overcomes this limitation and permits
the evaluation of both metabolic and anatomic characteristics of disease,
REF: Akram Al-Ibraheem. Clinical Applications of FDG PET & PET/CT in Head & Neck Cancer. Journal of Oncology, 2009.

14.  POINTS TO BE CONSIDERED IN FDG PET-CT IMAGE INTERPRETATION
Axial PET CT fused initial staging image (A) of a 62-year-old woman with right laryngeal cancer. The PET axial
image (B) and PET CT fused image (C) of a post radiation therapy restaging scan demonstrates a small focal uptake
in the right vocal cord at the exact site of primary lesion (A), consistent with residual disease. There is another small
focal uptake nearby on the same side of the primary lesion which was proven to be a 6-mm nodal metastasis (blue
arrows). This positive node was initially identified on the PET-only image (D) with better contrast over background
compared with the PET CT fused image (E).
1 Focal in appearance

15.  POINTS TO BE CONSIDERED IN FDG PET-CT IMAGE INTERPRETATION
Axial PET CT fused (A) and coronal (B) initial staging images of a 52-year-old man with superior pharyngeal
cancer. The primary lesion is located mostly on the left but crosses the mid line (arrow). There is intense FDG uptake
in an enlarged left cervical node and is consistent with local metastasis. There are mild FDG avid smaller right
cervical nodes (circle). Considering the location of the primary lesion, the right cervical nodes were considered
metastases and biopsy was recommended
2 Geographic location of the lesion

16.  POINTS TO BE CONSIDERED IN FDG PET-CT IMAGE INTERPRETATION
Axial PET CT fused (A), CT-only (B), and coronal PET-only (C) restaging images of a 63-year-old woman with left
nasopharyngeal cancer 2 years post radiation therapy. There is focal cancer recurrence in the left maxillary sinus
(arrows). There is asymmetric focal physiologic uptake in the right masseter muscle (circles) without a
corresponding morphologic change on CT. The left masseter muscle does not show uptake secondary to previous
radiation damage
3 Time since recent chemotherapy or radiation therapy

17. Proposed Standard Patient Preparation
Protocol for 18F-FDG PET and PET/CT
REF: Surasi et al. 18F-FDG PET and PET/CT
Patient Preparation: A Review of the Literature. J
Nucl Med Technol 2014; 42:5–13

18.  LIMITATIONS OF PET-CT
1 Physiologic FDG uptake
XII nerve dysfunction. (A) Axial CT image
shows fatty degeneration of the right half of
the tongue. (B) PET/CT shows increased FDG
avidity in the left (normal) half of the tongue
(paradoxical finding)
REF: Galal Omami et al. Basic principles and applications of
18F-FDG-PET/CT in oral and maxillofacial imaging: A
pictorial essay. Imaging Science in Dentistry 2014; 44: 325-32.

19.  LIMITATIONS OF PET-CT
2 Inflammatory changes
A 51-year-old man with a 3-year history of nasopharyngeal
carcinoma. The patient presented with new mucosal
swelling in the left retromolar trigon; recurrence was
suspected. PET-CT image shows increased metabolism in
the corresponding area (arrow); however, further clinical
examination and biopsy revealed a dental abscess.
REF: Galal Omami et al. Basic principles and applications of 18F-FDG-
PET/CT in oral and maxillofacial imaging: A pictorial essay. Imaging
Science in Dentistry 2014; 44: 325-32.

20.  LIMITATIONS OF PET-CT
3 Low FDG uptake
False-negative PET/CT overlooks nodal metastasis. (A) On
axial PET/CT, the lymph node (arrow) has low FDG uptake
belying nodal disease. (B) On axial contrast-enhanced CT, the
central necrosis and rounded configuration are clues to the
nodal metastasis; confirmed with further biopsies. A PET/CT
examination of such conditions may yield false-negative
findings (metastatic thyroid carcinoma).
REF: Galal Omami et al. Basic principles and applications of 18F-FDG-
PET/CT in oral and maxillofacial imaging: A pictorial essay. Imaging Science
in Dentistry 2014; 44: 325-32.

21.  CURRENT AND FUTURE CONCEPTS
IN RADIOTHERAPY IN HNSCC
REF: Cox et al. 18F-FDG-PET/CT-guided radiotherapy of cervical lymph nodes in head and
neck squamous cell carcinoma J Cancer Metastasis Treat 2021;7:25.

22.  SUMMARY
1. FDG PET/CT technology is outstanding for oral cavity lesions in patients with significant dental artifact shown on CT and
MRI scans.
2. FDG PET/CT has become essential for the staging and restaging of patients with head and neck cancer and for the
evaluation for distant metastasis.
3. Nearly half of unknown primary head and neck tumors that are undetectable by conventional CT or MRI can be located
by FDG PET/ CT scans.
4. A negative FDG PET/CT scan post treatment is a reliable indicator of a complete response to therapy and excellent
prognosis.
5. An FDG PET scan is not a tumor-specific scan, but rather a glucose uptake scan. Not all hot spots are cancers. Non-
cancerous FDG activity in a post-therapy scan may be confused as residual tumor/recurrence.
6. Pre-imaging patient instructions and imaging protocol are critical for a successful FDG PET/ CT scan

23.  REFERENCES
1. Eyassu E, Young M. Nuclear Medicine PET/CT Head and Neck Cancer Assessment, Protocols, And Interpretation. StatPearls
[Internet]
2. Wai Lup Wong, Vincent Batty. Role of PET/CT in maxillo-facial surgery. British Journal of Oral and Maxillofacial Surgery, 47
(2009) 259–267.
3. Akram Al-Ibraheem. Clinical Applications of FDG PET & PET/CT in Head & Neck Cancer. Journal of Oncology, 2009.
4. Adam et al. PET/CT scanner instrumentation, challenges, and solutions. Radiol Clin N Am 42 (2004) 1017 – 1032
5. Rosa Fonti et al. PET/CT in Radiation Oncology. Seminars in Oncology. 2019.
6. David Q. Wan. Advances in Functional Imaging in the Assessment of Head and Neck Cancer. Oral Maxillofacial Surg Clin N
Am 31 (2019) 627–635.
7. Surasi et al. 18F-FDG PET and PET/CT Patient Preparation: A Review of the Literature. J. Nucl. Med Technol. 2014; 42:51
13.
8. Galal Omami et al. Basic principles and applications of 18F-FDG-PET/CT in oral and maxillofacial imaging: A pictorial
essay. Imaging Science in Dentistry 2014; 44: 325-32.
9. Cox et al. 18F-FDG-PET/CT-guided radiotherapy of cervical lymph nodes in head and neck squamous cell carcinoma J
Cancer Metastasis Treat 2021;7:25.

24. THANK YOU