Study participants
Between April 2015 and March 2019, this retrospective study included 77 women, who had pathologically proven breast cancer, underwent whole-body PET/CT examination using PET/CT scanner (Gemini, Philips Medical Systems). Patients’ clinical records, charts, follow-up surveys, and aftercare files were retrieved, and relevant data were taken. Six patients were lost to follow-up; thus, the final number was 71 patients.
Inclusion criteria
Patients with pathologically proved breast cancer referred for PET/CT examination.
Exclusion criteria
The exclusion criteria are as follows: co-existence of another malignancy, recent biopsy or surgery, or local radiotherapy within 1 month before PET/CT scan.
Patient preparation
All patients were instructed to fast for 6 h before the PET scan. PET image acquisition was done 45 min after the intravenous administration of 18-FDG. The dose of the tracer was 0.09–0.17 mCi/kg. Control of blood glucose below 150 mg/dl was achieved.
Study instruments and technique
A whole-body PET/CT examination from the brain to the mid-thigh was done after 45 min of 18-FDG administration with both CT and PET covering identical areas. The acquisition time was 2.5 min per bed position with eight-bed positions. CT data were used for the attenuation-correction of PET images, and then the CT attenuation correction (CTAC) series were reconstructed. After PET scan, a contrast-enhanced CT study was conducted using nonionic contrast material (Iopamiron 370; Schering, Osaka, Japan).
Data management and analysis
Two radiologists experienced in nuclear medicine reviewed, interpreted, and analyzed PET images. Any foci of higher FDG than the back-ground, located away from areas of physiologically increased uptake, were considered to be positive on PET images. Lesions were analyzed semiquantitatively using SUV-max, defined as the ratio of maximum tissue FDG concentration per milliliter of tissue to the activity injected per gram of the patient’s body weight. Also, CT images were then analyzed blinded from the PET findings. Then, hybrid PET/CT images were then analyzed by both interpreters. All detected lesions, including all doubtful or contradictory findings between both modalities, were further investigated by clinical and radiological follow-up serves as a standard of reference. The following imaging modalities were used for follow-up: bone scintigraphy in 9 patients, whole spine MRI in 2 patients, and abdominal ultrasound in 3 patients.
Statistical analysis
To evaluate the diagnostic performance of PET and CT, the sensitivity, specificity, accuracy, positive, and negative predictive values were calculated for all lesions; also, agreement between both methods was tested by Cohen kappa (κ). The p value was considered significant if less than 0.05. Quantitative data were summarized and expressed as mean ± SD, median (range), whereas qualitative data were expressed as frequencies and percentages. To measure the agreement between CT and PET in detecting breast lesions, the analyses were carried out using SPSS (Version 23. SPSS Inc., Chicago, IL, USA).