FDG digital PET/CT more efficient than MRI in evaluation of recurrence soft tissue sarcoma.

1363 Objectives: Soft tissue sarcomas are a diverse group of neoplasms that witch can occur almost anywhere in the body. Their rarity, heterogeneity of subtype and location mean that developing evidence-based guidelines is complicated by the limitations of the data available [1]. The overall five‐year survival rate in patients with all-stages soft tissue sarcomas remains only 50% to 60%. Most patients die of metastatic disease, which becomes evident within two to three years after the prior diagnosis in 80% of cases [2]. In current oncology practices, CT and MRI imaging modalities guide diagnosis and ensure consistent and optimal treatment of patients with soft tissue sarcoma. Positron emission tomography (PET) imaging is studied in soft tissue sarcoma, but its utility remains to be defined [3, 4]. In this study, we investigate on the contribution of FDG PET/CT in nine cases of evaluation soft tissue sarcoma recurrence in which MRI cannot conclude. Methods: Nine patients (male n=5, female=4 ) aged 35 to 74 years old, previously operated for soft tissue sarcoma, underwent whole-body FDG digital PET/CT (Philips) in addition of MRI imaging to evaluate recurrence. FDG PET/CT was performed one hour after injection of 3MBq per kilo (range 184 to 357 MBq) for 14 minutes (1min/position bed from vertex to mid-tights and 30 sec/position bed on the legs). Results: Amongst the nine patients, 11 lesions were identified in various locations: leg, inguinal, interpectoral, buttock, forearm, trapezius muscle. Lesions were essentially local recurrence or metastases; size varied from 5 to 150 millimeters with 4 lesions less than 15 millimeters. SUV max uptake value range was 5 to 42 (median=6.8; mean ± SD = 12 ± 10.7). No correlation between size and SUV max uptake value was found (R2= 0.476). Out of the nine patients, three have concordant local recurrence results between MRI and FDG PET. Out of those three, two of them underwent curative surgical resection and the third benefited from systemic treatment. Out of the remaining six patients, PET FDG were discordant with MRI results; five MRI showed stable disease or post-treatment necrosis whereas FDG PET found progression disease after surgery or recurrence. Patients were finally treated by surgery or/and radiotherapy with positive recurrence sarcoma pathology analyses or/and good response to treatment. For the last discordance between MRI and PET, FDG PET was a false positive with negative pathology (hematoma), but the patient was subject to a strict follow-up (MRI every 2-3 months). Conclusions: Recent evolution of digital PET technology, with the improvement of the sensitivity and resolution, permit to identify smaller lesion [5]. FDG PET was allowed to distinguish recurrence from necrosis and post-operative changes. FDG PET whole body acquisitions compared to local MRI acquisitions was allowed to identify metastatic dissemination. In this study, FDG digital PET/CT exams were equal or superior to MRI alone in the identification of soft tissue sarcoma recurrence and found metastases. This exam could be very useful for biopsy and surgery guidance in soft tissue sarcomas. References: [1] A Dangoor, B Seddon, C Gerrand, R Grimer, J Whelan, I Judson. UK guidelines for the management of soft tissue sarcomas. Clin Sarcoma Res. 2016; 6: 20. [2] Pisters, P. Staging and Prognosis, in RE Pollock (ed). American Cancer Society Atlas of Clinical Oncology: Soft Tissue Sarcomas. Hamiliton, Ontario: BC Decker, Inc.; 2002: 80- 88. [3] R Kumar, A Chauhan, A K Vellimana, M Chawla. Role of PET/PET-CT in the management of sarcomas. Expert Review of Anticancer Therapy, vol. 6, no. 8, pp. 1241-1250, 2006. [4] D Roberge, SVakilian, YZ Alabed, RE Turcotte, CR Freeman, M Hickeson. FDG PET/CT in Initial Staging of Adult Soft-Tissue Sarcoma. Sarcoma. 2012; 2012: 960194. [5] Adler S, Seidel J, Choyke P, Knopp MV, Binzel K, Zhang J, Barker C, Conant S, Maass-Moreno R. Minimum lesion detectability as a measure of PET system performance. EJNMMI Phys. 2017; 4(1):13.