18F-FDG Tumor Imaging Clinical Applications
The most frequent and useful indications for FDG PET imaging are listed below. This technique may especially be employed to differentiate malignant from benign lesions, if the level of uptake is considered. Normally malignant processes pick up glucose intensively and corresponding SUV are clearly elevated in the majority. This may help in the diagnosis of a primary tumor. In cases where this tumor is unknown FDG PET can detect up to 30% to 40 % of these primaries.
Head and Neck: Head and Neck Cancers Pituitary Adenoma Thyroid Follicular Carcinoma
Thorax: Lung Cancer Breast Cancer
Gastrointestinal: Esophageal Cancer Pancreatic Carcinoma Colorectal Cancer Gastric Carcinoma
Hematologic: Lymphomas Multiple Myeloma
Gynecologic: Endometrial Cancer
Skin: Melanoma
Other indications comprise staging, and therapy monitoring. This is particularly valuable because PET can depict cell metabolism in a direct way and characterize tumoral viability. Normally, sensitivity is over 90% in the detection of secondary extension of the malignancies commented above.
Nonetheless, it must be known that in some metastatic conditions FDG PET value may be limited. It is the case of peritoneal carcinomatosis. Dromain C et al. reported 30 patients with suspected peritoneal carcinomatosis of gastrointestinal tract. All patients had been operated on the primary tumor. Colon 50%, Appendix 33%, Rectum 10%, Stomach 3.5%, Small Bowel 3.5%. The sensitivity for the diagnosis of peritoneal carcinomatosis was 57% for PET-CT (3). This is explained in most cases due the small size of the lesions and the diffuse rather than focal involvement.
False positives were as follows: pneumoniae, tuberculosis, sarcoidosis,
cryptococcosis, thrombosis, bronchitis, costochondritis, radiation pneumonitis,
artifact due to respiratory movements, catheters,
thyroid and adrenal adenomas, osteophytes, fractures, abscess, foreign body,
surgical wounds, ostomies, prosthesis, degenerative joint diseases,
osteomyelitis, amyloidosis, pancreatitis, myositis, gastritis, colitis, herpes
zoster. FDG should be injected 4-6 h after insulin administration
otherwise it will concentrate
markedly in the muscles. Brown fat
reinforces its uptake up to
50% in late images (4). Consider also
silicosis. Likewise, brown fat FDG uptake has to ruled out as cause of false positive study (5).
Patients on Chemotherapy and bone marrow agents, may present with diffuse marrow homogeneous uptake, which later on becomes normal.
References:
1 Simo M. Utilidad de la Tomografia PET en cancer de mama, p: 535-541 and Setoain X. PET en los linfomas, p: 543-547. En Medicina Nuclear Aplicaciones Clínicas. Eds: I. Carrio - P. González. Editorial Masson, Barcelona España, 2003.
2 Rohren EM, Turkington TG, Coleman RE. Clinical applications of PET in oncology. Radiology. 2004 May;231(2):305-32.
3 Dromain C, Leboulleux S, Auperin A, Goere D, Malka D, Lumbroso J, Schumberger M, Sigal R, Elias D. Staging of peritoneal carcinomatosis: enhanced CT vs. PET/CT.Abdom Imaging. 2008 Jan-Feb;33(1):87-93.
4 Del Rocío Estrada-Sánchez G, Altamirano-Ley J, Ochoa-Carrillo FJ.Normal variants and frequent pitfalls with (18)FDG PET/CT study.Cir Cir. 2007 Nov-Dec;75(6):491-7.