Dual-time FDG-PET/CT in patients with potential breast cancer recurrence: Head-to-head comparison with CT and bone scintigraphy

Dual-time FDG-PET/CT in patients with potential breast cancer recurrence: Head-to-head comparison with CT and bone scintigraphy

 Kirsten Falch, Christina Baun, Oke Gerke, , Ziba A. Farahani, Poul F. Høilund-Carlsen, Lisbet B. Larsen*, Marianne Ewertz**, Katrine Søe*** and Malene G. Hildebrandt Departments of Nuclear Medicine, *Radiology, **Oncolocy, and ***Surgery, Odense University Hospital, Odense, Denmark

Purpose: Breast cancer (BC) is the most common type of cancer among women in Denmark and about 1/3 of the affected women experience recurrence. The prognosis is good if loco regional recurrence is diagnosed early while metastatic illness is considered to be non-curable with a median survival of approx. two years. Depending on the symptoms of the patient a wide variety of modalities is used in the diagnostic work-up. For accurate staging and prognosis contrast-enhanced computed tomography (CT) of the thorax and the upper abdomen is used when looking for organ and lymph node metastases and if osseous metastases is suspected, bone scintigraphy is the preferred modality. Other modalities such as magnetic resonance imaging (MRI) are often used as a supplement to confirm or refute equivocal findings. The work-up in this patient group can be time consuming and a tiring procedure for the patient due to multiple inclusion pathways and - sometimes - the need for multiple imaging procedures. Whole body positron emission tomography/computed tomography (PET/CT) with 18fluorodeoxyglucose (FDG) is able to supply functional information with morphology. The literature shows that some breast carcinomas have low metabolic activity which can lead to false negatives when the study technique involves a single time-point acquisition . Several studies have demonstrated that FDG uptake continues to increase for several hours after injection in various malignant lesions while benign lesions, such as inflammatory lesions, decrease. Due to the difference in the time-activity curves for malignant and benign processes late imaging should hypothetically increase the accuracy of the modality in detecting recurrent BC. Multiple time-point or delayed single time-point FDG PET/CT imaging has the potential to become a one-stop-shop for diagnosing recurrence and thereby optimize the work-up in this patient group. This article presents the results of the interim analysis of the first 39 patients in our study designed to evaluate the diagnostic accuracy of FDG PET/CT performed one and three hours after injection compared with CT and bone scintigraphy in patients suspected of BC recurrence Methods and materials: 39 patients suspected either clinically or diagnostically of BC recurrence were included. All patients underwent FDG PET/CT, routine bone scintigraphy and CT of the chest and upper abdomen within 2 weeks. Patients with other malignancies, pregnant or lactating women, patients younger than 18 years and patients with confirmed metastatic disease were not eligible FDG PET/CT. All patients fasted for a minimum of six hours and had a blood glucose level less than 8 mmol/l prior to injection of 4 MBq/kg of FDG. Imaging was performed 1 and 3 hours (±5 mins) after injection. At both time-points a low-dose CT from the skull to the proximal femur was obtained followed by a 3D PET-scan of the same area. The duration of the PET-scan was adjusted according to body mass index (BMI) ie. 2½ min/bed position when BMI was between 18.5 and 24.9. If BMI was either lower or higher the scan time was decreased or increased by ½ min/bed position, respectively. At the late time-point the scan time was prolonged by 1 min/bed position. CT. Contrast-enhanced diagnostic CT of the thorax and the upper abdomen was performed at the Department of Radiology according to their current guidelines. The patients were scanned from the seventh cervical vertebra to the upper abdomen including the liver. 100 ml of Optiray 300 mg I/ml were administered with a flow of 3.0 ml/s and a delay of 60 seconds. Bone scintigraphy. The patients were injected with 700 MBq 99mTc-DPD 3 to 4 hours prior to whole body imaging. In the waiting period the patients were asked to drink approx. 1 litre of clear liquids. Positive findings with any of the three modalities were verified by biopsy. If biopsy was impossible, a composite reference comprising all available imaging procedures and follow-up data was used as gold standard. Sensitivity, specificity, accuracy, positive and negative predictive values (PPV/NPV) and likelihood ratio of positive and negative test (LRpos/LRneg) were calculated for PET/CT, CT and bone scintigraphy for diagnosis of recurrent BC for both patient based and lesion based analysis. Comparison between modalities was performed true to the methodology and field-of-view of the respective modality, i.e. bone scintigraphy was only compared with bone lesions found in CT and FDG PET/CT in the comparable field-of-view and likewise for comparison of the other modalities. Results: 13 patients (43%) showed recurrence with a total of 74 lesions. On a patient basis, 1-hour and 3-hour FDG-PET/CT had the same sensitivity and specificity: 77% and 93%, respectively. The corresponding values for CT were 54% and 100%, respectively, and for bone scintigraphy 86% and 68%, respectively. On a lesion basis, sensitivity and specificity were 80% and 90% for 1-hour FDG-PET/CT and 84% and 90%, respectively, for the 3-hour scan. CT and bone scintigraphy had sensitivities of 67% and 81% and specificities of 100% and 48%, respectively. Conclusion: These interim results suggest that FDG PET/CT may have a role in the diagnostic work-up of patients with suspected recurrent breast cancer. The 3-hour FDG-PET scan may be diagnostically superior to the other modalities.