Accurate diagnosis of recurrence and re-staging in ovarian cancer is important in an effort to improve the poor prognosis. Re-staging radiologic studies are complicated by alterations to the anatomy and physiology of the abdomen/pelvis from surgery and radiation. Moreover, the ability to fully evaluate the patient in one combined imaging modality rather than multiple tests is advantageous if the performance of that test is equal to or better than the others.
There has long been interest in the role of PET in ovarian carcinoma, but the majority of studies in the current literature are primarily based on dedicated PET acquisitions (10
). Both early (15
) as well as recent studies (13
) with dedicated PET have shown comparable or higher sensitivity, specificity, and diagnostic accuracy in comparison to conventional imaging or tumor markers.
However, there is evidence that PET plus CT performs better than either alone in various solid cancers including ovarian cancer (27
). There are relatively few studies published on concurrent PET/CT in gynecologic malignancy (29
). A recent prospective study (32
) in 97 patients, evaluating the utility of PET/CT for the evaluation of a pelvic mass of unknown origin (with post-surgical histopathologic follow-up) found that the sensitivity and specificity for PET/CT in diagnosing a malignant pelvic tumor were 100% and 93%, respectively. Other studies evaluating PET/CT in recurrent ovarian cancer also show promising results. Three retrospective studies (29
) evaluating PET/CT in recurrent ovarian cancer provide sensitivity and specificity values of 83–95%, and 71–100%, respectively, which are, again, superior to that reported in the literature for conventional imaging. And, another (35
) showed that a change in the clinical management was observed in 44% of cases when PET/CT information was added to conventional follow-up findings.
With these considerations in mind, PET/CT shows promise in the restaging evaluation of ovarian cancer. Our study confirms this with an overall per patient sensitivity of 88% and specificity of 88% for detection of ovarian cancer at restaging. In comparison, conventional imaging has a reported sensitivity of 53–70% and specificity of 82–83% (13
One group has demonstrated improved sensitivity and specificity of PET/CT for the evaluation of recurrent ovarian carcinoma when their early experience was compared to later. Sensitivity improved from78% to 93% and specificity from 75% to 100% (30
). This indicates that as experience grows with this relatively new modality, the accuracy will increase.
The results in our study showed a lower sensitivity of 81% for lesions in the pelvis compared to 96% for disease in other sites. This difference is likely due to post-surgical and post-treatment induced inflammatory uptake within the pelvis. This hypothesis is supported by a study (32
) showing that staging with PET/CT (before surgery) has sensitivity and specificity of 100%, and 92%, respectively, in comparison to subsequent histopathologic findings. Nonetheless, conventional imaging is also complicated by post-therapy changes, such that the reported sensitivity and specificity remains higher with PET/CT. Another contributing factor to these results may be to post-therapy anatomical changes accounting for challenges in interpretation of non-contrast enhanced CT images. Using i.v. contrast-enhanced pelvic CT may result in improved sensitivity in this location for patients with ovarian cancer. The specificities were equal at 94% for pelvic and extra-pelvic lesions.
Outside the pelvis, both the sensitivity and specificity are high, indicating the very good performance of PET/CT in identifying more distant lesions. Extra-pelvic lesions were located in the liver, lungs, omentum, bones, and lymph nodes. This is significant in terms of altering the management, as shown in one study which found that a change in clinical management was observed in 44% of cases when PET/CT information was added to conventional follow-up findings (35
The limitations in this study acknowledge that patient selection in referrals for PET/CT is important for the results of the scan. However, this is difficult to overcome in any retrospective review.
Taken together, the results of this study confirm a high sensitivity and specificity of PET/CT in ovarian cancer staging both within and outside the pelvis. The values reported in this study are in accord with those reported in the literature thus far and add to the limited number of studies on this important subject. The main advantages of PET/CT for ovarian cancer are in restaging, finding extra-pelvic lesions that can effect patient management, and in evaluation of those patients with increased CA-125 levels. The sensitivity of PET/CT is lower within the pelvis, probably due to post-operative changes and lack of i.v. contrast, but remains higher than conventional imaging. The latter, however, is established and remains important for its improved resolution. Therefore, the combined use of conventional imaging and PET/CT in the evaluation of ovarian cancer is recommended.