PET IN OVARIAN CARCINOMA (POCA): AN IAEA INTERNATIONAL COOPERATIVE STUDY (E.1.30.50)

Ovarian carcinomas (OC) are rarely diagnosed in the early stage, without peritoneal spread (<5% of cases) while more than 90% presents with spread to the peritoneum and beyond. Common metastatic sites include liver, lung, spleen, transmural involvement of intestine, and skeletal metastases as well as involvement of the inguinal, supraclavicular, and axillary nodes. Cytoreductive surgery and chemotherapy are standard of care treatment in OC. Laparotomy and conventional imaging play important role in the precise assessment of tumour extent (primary tumour and peritoneal sites, regional lymph nodes, and distant sites) and deciding for primary surgery or neoadjuvant treatment. However, several anatomic locations such as retro-hepatic areas, retroperitoneal spaces, porta hepatis, are difficult to explore and up to 30% of patients are understaged at laparotomy, due to unexpected peritoneal or extra-abdominal (nodal or extranodal) spread.

Therefore, accurate presurgical staging is essential. Contrast-enhanced CT (ceCT) is useful to detect peritoneal spread of tumour and metastatic lesions, but despite being considered the modality of choice, its accuracy in staging OC ranges from 53% to 92%. with limited ability to detect small cancer implants on bowel surfaces, mesentery and parietal peritoneum. MR imaging demonstrates advantages relative to ceCT in evaluating metastatic spread in OC due to its higher soft tissue contrast and lack of radiation exposure. On MRI, lesions may be obscured by spleen or distortion artifacts. Moreover, MR imaging does not overcome the problem of diagnosing lymph nodal and peritoneal sites of malignancy by size criteria. Currently, MR imaging could be considered a second-line technique, in patients with contraindications to ceCT and/or in patients with inconclusive ceCT findings.

Nearly 40% of relapses following primary treatment of epithelial ovarian cancer with surgery and chemotherapy for stage 3 disease ( Nearly 70% of cases at presentation ) are extra abdominal which will be missed by conventional radiological procedures like CT and MRI abdomen. There is a need for imaging modalities with better diagnostic accuracy in staging OC. Glucose transporter 1 (GLUT-1) over-expression and microvessel density/tumour proliferation lead to high 18F-FDG uptake in OC. There is a high chance of picking them up early in primary and relapse setting using PET which can modify the mode and intensity of treatment and improve survivals. Thereby, 18F- FDG PET/CT may overcome limitations of conventional imaging in the preoperative staging of OC

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patients. Various studies have evaluated the role of 18F-FDG PET/CT in evaluation of suspected OC, staging and most important, in biochemical recurrence proving its advantage over ceCT. 18F- FDG PET/CT has better diagnostic performance compared with conventional imaging for the evaluation of the lymph node involvement (even sub-cm nodes), extra-abdominal spread, and detection of unsuspected extra abdominal spread and other malignant tumours being a whole body technique, leading to upstaging of disease in a significant percentage of patients and alter therapeutic decision making. A study showed that the sensitivity of 18F-FDG PET and ceCT is not the same in the different portions of the abdominopelvic cavity. However, literature is still limited and 18F-FDG PET is not routinely used in staging OC. The present study aims to compare 18F- FDG PET/CT and ceCT in the presurgical evaluation of peritoneal carcinomatosis in ovarian cancer patients.