Joint Program in Nuclear Medicine

PET and Melanoma Staging

Pritinder K. Thind, MD
Kevin J. Donohoe, MD

February 15, 2000

Presentation

Imaging Findings

A repeat FDG scan after repeat surgery demonstrated diminished uptake in the right axilla compatible with the recent incomplete resection and persistent uptake in the right neck (reprojection images and selected coronal sections with arrows).

Discussion

• Increased rate of glycolysis
• Increased hexokinase/glucose-6-phosphatase enzyme ratio
• FDG is metabolically trapped in neoplasms due to the 2-deoxy modification
  • Prevents further biodistribution

Normal FDG distribution:

• Brain cortex: glucose is used as a substrate
• Myocardium: variable uptake
  • Fasting state: free fatty acids
  • Post prandial or after a glucose load: glucose
• Kidneys/genitourinary tract: route of FDG excretion
  • Consider diuretics, Foley catheter
• Musculature: diffuse, symmetric, follows muscle anatomy
  • Avoid exercise and prolonged walking
• Gastrointestinal tract: lymphoid tissue, cecum, gastric wall and esophagus

Patient preparation:

• Know history, recent therapeutic, and interventional procedures
• 4 hour fast: no drinks with sugar, no intravenous dextrose
  • Consider 12 hour fast if chest is to be imaged to prevent myocardial uptake
• Encourage hydration and diuresis
  • Limits genitourinary artifacts
  • Diminishes radiation dose to the bladder
• Promote relaxation, avoid muscular activity

Melanoma:

• Rapidly increasing in incidence in the United States
• Accounts for the vast majority of deaths due to cutaneous neoplasms
• Poor response to chemotherapy and immunotherapy regimens
• Early detection and surgical resection are key to improving prognosis
• Primarily local and lymphatic spread, but also hematogenously
• If deep primary lesions or regional metastases are present, distant metastatic disease is more likely
• Resection of solitary or localized metastases improves survival
• After the diagnosis of distant metastases, the median survival is approximately 4 to 6 months

PET and melanoma staging:

• Improve patient selection for surgery
• Potential in monitoring treatment response
• May be cost effective modality in staging
• Improve detection of metastases
• Adjuvant to other modalities

Damien et al:

• 100 melanoma patients
• 415 metastatic lesions, 388 (93%) detected by PET
• 24 metastases were detected up to 6 months earlier
• Surgical and/or medical management was altered in 22 patients

Time between PET and conventional detection, Grittters et al:

• 12 patients
• Sensitivity for intra-abdominal visceral and lymph node metastases: 100%
  • 3 foci, retrospective on CT
  • 2 foci seen on follow-up CT
• Superficial nodes: accuracy of 100%
• Sensitivity for small pulmonary lesions was lower than CT
  • Respiratory motion
  • Prior cancer treatment
• PET can detect tumour in superficial nodes, including sub clinical metastases in normal sized nodes
• PET had a lower sensitivity than CT in pulmonary metastases <1.0 cm in size
  • Prior treatment
  • Blurring due to respiratory motion (non-gated)
  • ? Limited resolution due to lower density of normal lung tissue and increased positron range

Wagner et al:

• FDG-PET in the detection of non-palpable regional lymph nodes
• 11 patients; 12 scans; 12 operations to clear 14 regional lymph node basins
• Sensitivity and specificity of 100%
• An area of increased uptake in a non-palpable lymph node basin is indicative of sub clinical or residual metastatic disease

Planar Coincidence Scintigraphy versus PET, Steinert et al.:

• Methods
  • Full-ring dedicated PET
  • Anterior and posterior planar projections simulating planar coincidence scintigraphy using a dual-head Anger camera were reformatted from the PET raw data
• 108 lesions (76 proven to be metastases) in 55 patients
• Sensitivities: 89% and 18% for PET and planar coincidence scintigraphy, respectively
• Missed lesions in coincidence scanning
  • Lesions in regions of high background activity-abdomen
  • Lesions < 22 mm in diameter
  • Inability to tolerate high counting rates
  • With planar data, lesion detection sensitivity is less than half that of tomographic data

Role of PET in Malignant Melanoma:

• Isolated lesions found on PET can be excised
• If multiple lesions are identified, can avoid unnecessary surgery
  • Chemotherapy
  • Immunotherapy
• Quantification of FDG uptake may have a role in monitoring treatment response

References

1. Boni et al. Staging of metastatic melanoma by whole-body positron emission tomography using 2-fluorine-18-fluoro-2-deoxy-D-glucose. British Journal of Dermatology 1995; 132: 556-562.

2. Damien et al. Positron emission tomography in the detection and management of metastatic melanoma. Melanoma Research 1996; 6: 325-329.

3. Delbeke, D. Oncological applications of FDG PET imaging: brain tumors, colorectal cancer, lymphoma and melanoma. The Journal of Nuclear Medicine 1999; 40: 591-603.

4. Gritters et al. Initial assessment of positron emission tomography using 2-fluorine-18-fluor-2-deoxy-D-glucose in the imaging of malignant melanoma. The Journal of Nuclear Medicine 1993; 34: 1420-1427.

5. Jadvar et al. The effect of fluorine-18-fluorodeoxyglucose positron emission tomography on the management of cutaneous malignant melanoma. Clinical nuclear medicine 2000; 1: 48-51.

6. Steinert et al. Planar coincidence scintiraphy and PET in staging malignant melanoma. The Journal of Nuclear Medicine 1998; 39: 1892-1897.

7. Wagner et al. Initial assessment of positron emission tomography for the detection of nonpalpable regional lymphatic metastases in melanoma. Journal of Surgical Oncology 1997; 64: 181-189.

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