الفهرس 
Incidence & Epidemiology
Physics of PET/CT scanOnly 14 pages are availabe for public view
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Abstract
Occult primary tumor or cancer of unknown primary (CUP) is defined as a biopsy-proven malignancy whose anatomical origin remains unidentified after a thorough diagnostic evaluation. Evaluation should include a detailed medical history, complete physical examination including pelvic and rectal examination, full blood count and biochemistry, urinalysis and stool occult blood testing, histopathological review of biopsy material with the use of immunohistochemistry, chest radiography, computed tomography (CT) of the abdomen and pelvis, and, in certain cases, mammography. FDG PET/CT an alternative, noninvasive imaging modality with a high diagnostic yield considered an excellent problem-solving tool in patients with CUP, Because of its high sensitivity for the detection of lesions, combined 18F-fluoro-2-deoxyglucose positron emission tomography (FDG PET)/computed tomography (CT) may be an excellent alternative to CTalone and conventional magnetic resonance imaging in detecting the unknown primary tumor. Occult primary tumor is detected in 5% -10 % of all cancer patients. In CUP, conventional tests discover only 20–27% of primary sites. The aim of this work was to assess the role of PET/CT in detection of an occult primary tumor. In this work PET/CT was performed for 63 patients with CUP syndrome (12/63 patients had lymph nodes, 12 had skeletal metastases, 11 patients had liver metastases, 4 had brain metastases, 4 patients had malignant pleural effusions, 4 had malignant ascites, 5 patients had lung nodules, 2 had peritoneal nodules, 2 had adrenal metastases and 7 had more than one site). Among those 63 patients included in the study, 34 patients had cytology proved metastatic lesion & the remaining 29 patients had clinical & radiological suspicion of the presence of a malignancy. All included patients were imaged by PET/CT scanner 60minutes post IV injection of 0.14 mCi/kg of body weight with F-18 FDG. Images were evaluated and cases of suspicion of primary tumor were verified by correlation with all clinical, pathological & follow up information. In this study PET/CT was able to detect primary tumor site in 40 of the 63 patients (63.5%).The reported locations for primary tumor were as follow: 10 patients in lung, 9 GIT (4 pancreas, 3 liver & 2 colon), 5 breast, 5 female genitalia (3 ovarian, 2 uterine), 2 prostate, 4 renal, and 5 head & neck (3 thyroid, & 2 pharyngeal). Five out of 63 (7.9 %) patients, proved to be false positive in PET/CT after pathologic assessment (chronic gastric ulcer, fibrohaemangioma, sarcoidosis, tuberculosis & inflammatory lymphadenopathy). 18 out of 63 patients , no site of a primary could be detected by PET/CT, however 14 patients of them (22.2 %) were proven by follow up to be True-Negative (TN), the remaining 4 patients with negative PET/CT study that during follow up the primary tumor sites were detected (2 patients had multiple myeloma, one patient had cancer colon & one patient had cancer stomach). So PET/CT in detection of unknown primary had a sensitivity of 91% & specificity of 74%, indicating that it is an effective study and demonstrating the advantage of metabolic information over conventional imaging methods in the search for a malignancy.