Abstract P5-01-07: Fidelity of FDG-PET in breast cancer: Reproducibility at multiple sites

Introduction Breast cancer is a common, treatable malignancy, with frequent metastasis to bone. Patients with bone-dominant disease are often excluded from clinical trials due to a lack of RECIST "measurable" disease. FDG-PET can help quantitatively measure multiple tumor sites, and assay disease activity in bone. However, the reproducibility of FDG-PET at multiple sites is unproven. We sought to pilot alignment of clinical protocols prior to imaging, phantom testing and then repeat patient scans, in patients undergoing clinical FDG-PET to test the fidelity of quantitative FDG-PET imaging. Methods After determination and alignment of clinical protocols, and serial successful phantom imaging, ten female patients with metastatic breast cancer underwent paired FDG-PET/CT test-retest studies with no more than 15 days between scans and without interim change in treatment. Seven patients were studied in the same scanner and 3 patients were studied in 2 different scanners in our clinical network. Each PET/CT scanner’s quantitative performance was monitored with NIST-traceable reference sources to ensure proper calibration. Images were interpreted and SUV metrics were estimated at a central lab. Linear mixed models with a random intercept were fitted to compare test-retest differences in multiple lesions per patient. Results SUVmax was assessed in a total of 68 lesions (52 bone, 16 other sites). Average SUVmax ranged from 2.3 to 18.2 (mean±SD = 5.7±2.6) per patient. The median SUVmax difference was 0.25 (5%) for 35 lesions imaged twice in the same scanner, and was 0.01 (0.2%) for 33 lesions imaged in two different scanners. In a linear mixed-effects model with random patient effects, there was no difference in average percentage SUV difference for the same scanner versus different scanners (p=0.70). In the same model, the absolute percentage difference in SUVmax for bone lesions was estimated as 6 percentage points lower than for other sites (p=0.002, 95% confidence interval 2%-10%). Conclusions If PET/CT systems are carefully calibrated, and imaging protocols are consistent, then variability associated with FDG SUVmax between scans is similar to prior test-retest studies. Bone lesions appear to have tighter reproducibility than soft tissue lesions. Clinical trials that utilize quantitative PET/CT imaging throughout a network of calibrated PET/CT scanners could increase patient recruitment and improve confidence in trial results. Accrual is ongoing and results will be updated. Research support Supported by NIH grant U01-CA148131 and NCI-SAIC Contract 24XS036-004. Citation Format: Hannah M Linden, Jennifer Specht, Lanell Peterson, Brenda Kurland, Andrew Shields, Darrin Byrd, Alena Novakova, Rebecca Christofel, Mark Muzi, David Mankoff, Kinahan Paul. Fidelity of FDG-PET in breast cancer: Reproducibility at multiple sites [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P5-01-07.