Clinical impact of whole body FDG-PET for recurrent biliary cancer: a multicenter study

Integrated FDG-PET/CT contribution over cross-sectional imaging in recurrence or progression of pancreaticobiliary neoplasms

PURPOSE

We aim to compare FDG-PET/CT and cross-sectional imaging (contrastenhanced CT/MRI) diagnostic abilities in detecting recurrence/progression of pancreaticobiliary system tumors and to reveal the clinical impact of integrated FDGPET/CT to CT/MRI on patient management.

MATERIALS AND METHODS

FDG-PET/CT and CT/MRI scans of 70 patients from initiation of treatment until proven recurrence/progression were retrospectively evaluated. FDGPET/CT and contrast-enhanced CT/MRI accuracy, sensitivity, specificity, PPV and NPV are compared in terms of overall recurrence/progression diagnosis and sitespecific concern; local disease, local lymph node, and distant organ metastasis. The impact of integrated FDG-PET/CT on patient management is scrutinized.

RESULTS

CT/MRI has higher sensitivity than FDG-PET/CT in detecting loco-regional involvement (90% vs 76.7% P: 0.152), local lymph node metastasis (88.9% vs 77.8%, P: 0.380) and distant organ metastasis (96.5% vs 80.7%; P: 0.006) in tumor recurrence/progression. In overall diagnosis, CT/MRI is more sensitive and accurate but less specific than FDG-PET/CT (92.3% vs 87.7%; 87.1% vs 84.2%; 40% vs 20%, respectively). In 8% (6/70) of patients FDG-PET/CT had a major impact on patient management.

CONCLUSION

FDG-PET/CT and cross-sectional imaging have different advantages and shortcomings. In recurrence/progression, recognition of early changes is more feasible by CT/MRI. However, inconsistency of morphologic and metabolic findings is important reason of cross-sectional imaging failure. FDG-PET/CT is superior in showing extraabdominal metastases, but missing small-volume lesions and misinterpreting inflammatory changes are still a problem lowering its sensitivity. Nevertheless FDGPET/CT is good option for guiding undetermined imaging findings or clinic-radiologic mismatch.

18F-fluorodeoxyglucose positron emission tomography (18FDG-PET) for patients with biliary tract cancer: Systematic review and meta-analysis

BACKGROUND & AIMS

The role of ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸FDG-PET) in the diagnosis and staging of patients with biliary tract cancers (BTCs) remains controversial, so we aimed to provide robust information on the utility of ¹⁸FDG-PET in the diagnosis and management of BTC.

METHODS

This systematic review and meta-analysis explored the diagnostic test accuracy of ¹⁸FDG-PET as a diagnostic tool for diagnosis of primary tumour, lymph node invasion, distant metastases and relapsed disease. Subgroup analysis by study quality and BTC subtype were performed. Changes in management based on ¹⁸FDG-PET and impact of maximum standardised uptake values (SUVmax) on prognosis were also assessed. A random effects model was used for meta-analyses.

RESULTS

A total of 2,125 patients were included from 47 eligible studies. The sensitivity (Se) and specificity (Sp) of ¹⁸FDG-PET for the diagnosis of primary tumour were 91.7% (95% CI 89.8-93.2) and 51.3% (95% CI 46.4-56.2), respectively, with an area under the curve (AUC) of 0.8668. For lymph node invasion, Se was 88.4% (95% CI82.6-92.8) and Sp was 69.1% (95% CI 63.8-74.1); AUC 0.8519. For distant metastases, Se was 85.4% (95% CI 79.5-90.2) and Sp was 89.7% (95% CI86.0-92.7); AUC 0.9253. For relapse, Se was 90.1% (95% CI 84.4-94.3) and Sp was 83.5% (95% CI 74.4-90.4); AUC 0.9592. No diagnostic threshold effect was identified. Meta-regression did not identify significant sources of heterogeneity. Sensitivity analysis revealed no change in results when analyses were limited to studies with low risk of bias/concern. The pooled proportion of change in management was 15% (95% CI 11-20); the majority (78%) due to disease upstaging. Baseline high SUVmax was associated with worse survival (pooled hazard ratio of 1.79; 95% CI 1.37-2.33; p <0.001).

CONCLUSIONS

There is evidence to support the incorporation of ¹⁸FDG-PET into the current standard of care for the staging (lymph node and distant metastases) and identification of relapse in patients with BTC to guide treatment selection; especially if the identification of occult sites of disease would change management, or if diagnosis of relapse remains unclear following standard of care imaging. The role for diagnosis of the primary tumour remains controversial due to low sensitivity and ¹⁸FDG-PET should not be considered as a replacement for pathological confirmation in this setting.

LAY SUMMARY

A positron emission tomography (PET scan), using ¹⁸F-fluorodeoxyglucose (¹⁸FDG), can help doctors identify areas of cancer in the body by highlighting "hot spots". These hotspots may be cancerous (true positive) but may also be non-cancerous, like inflammation (false positive). We show that PET scans are useful to assess how far advanced the cancer is (by assessing spread to lymph glands and to other organs) and also to identify if the cancer has recurred (for example after surgery), thus helping doctors to make treatment decisions. However, a biopsy is still needed for the initial diagnosis of a biliary tract cancer, because of the high chance of a "false positive" with PET scans.

Effects of the Obesity Type on FDG-PET Image Quality

PURPOSE

The aim of our study is to evaluate whether an ¹⁸F-FDG PET/CT image quality is influenced by the obesity type visceral fat or subcutaneous fat.

METHODS

We chose continuously 68 patients with obesity (35 subcutaneous fats and 33 visceral fats) who underwent an ¹⁸F-FDG PET/CT scan at our clinic from January 3, 2015 to June 30, 2015. And then, we calculated the noise equivalent count (NEC_density), the signal to noise ratio of the liver (SNR_liver), and the ratio of random coincidence counts to total prompt (random/prompt countrate) on each PET/CT image.

RESULTS

We observed that NEC_density was decreased as the body mass index (BMI) and the abdominal circumference increased regardless of the obesity type. When the BMI was on the same degree between two types, however, NEC_density of a visceral fat was 21.6% that is inferior to that of subcutaneous fat on the average. A similar relation was satisfied also in abdominal circumference. Conversely, random/prompt countrate of a visceral fat was more than that of subcutaneous fat when the abdominal circumference and BMI were on the same degree, respectively. Overall, random/prompt countrate tended to increase as BMI and the abdominal circumference increased. With respect to SNR_liver, the value of a visceral fat was inferior to that of subcutaneous fat unconditionally.

CONCLUSION

When the BMI and abdominal circumference are on the same degree, respectively, the ¹⁸F-FDG PET/CT image quality of visceral fat is inferior to that of subcutaneous fat. The measure is to extend the collection time by about 20% in the pelvic area from the abdomen of visceral fat type obesity.

[Usefulness of Determining Acquisition Time by True Count Rate Measurement Method for Delivery 18F-FDG PET/CT]

A stable quality of delivery 18F-fluoro-2-deoxy-D-glucose (18F-FDG) positron emission tomography/computed tomography (PET/CT) requires suitable acquisition time, which can be obtained from an accurate true count of 18F-FDG. However, the true count is influenced by body mass index (BMI) and attenuation of 18F-FDG. In order to remove these influences, we have developed a new method (actual measurement method) to measure the actual true count rate based on sub-pubic thigh, which allows us to calculate a suitable acquisition time. In this study, we aimed to verify the acquisition count through our new method in terms of two categories: (1) the accuracy of acquisition count and (2) evaluation of clinical images using physical index. Our actual measurement method was designed to obtain suitable acquisition time through the following procedure. A true count rate of sub-pubic thigh was measured through detector of PET, and used as a standard true count rate. Finally, the obtained standard count rate was processed to acquisition time. This method was retrospectively applied to 150 patients, receiving 18F-FDG administration from 109.7 to 336.8 MBq, and whose body weight ranged from 37 to 95.4 kg. The accuracy of true count was evaluated by comparing relationships of true count, relative to BMI or to administered dose of 18F-FDG. The PET/CT images obtained by our actual measurement method were assessed using physical index. Our new method resulted in accurate true count, which was not influenced by either BMI or administered dose of 18F-FDG, as well as satisfied PET/CT images with recommended criteria of physical index in all patients.