COMPARISON OF PET/CT IMAGES WITH 18F-FDG AND 18F-PSMA-1007 IN MUSCULOSKELETAL TUMORS TO EVALUATE THE POTENTIAL OF THERANOSTICS APPROACH

Abstract

Introduction/Justification: Sarcomas are malignant tumors in the bone, cartilage, fat, muscles, and vessels. Sar- comas are highly heterogeneous due to the wide variety of histological subtypes and various ana- tomical locations, and thus, the diagnosis and management of these tumors are challenging. Beyond sarcomas, the musculoskeletal system is a frequent site of metastatic tumors and multiple myeloma with lesions that present difficult local control. Imaging exams such as MRI and 18F-FDG (FDG PET/CT) to assess the extent of these tumors play a crucial role in managing these patients. How- ever, PET/CT imaging with 18F-PSMA-1007 (PSMA PET/CT) may be a more interesting diagnostic marker due to the potential Theranostics implications. Objectives: This study aimed to compare the performance of FDG PET/CT and PSMA PET/CT images in patients with advanced-stage unresectable recurrent and metastatic musculoskeletal tumors. Materials and Methods: Patients underwent FDG PET/CT and PSMA PET/CT imaging with a 24-hour interval be- tween studies. Two nuclear medicine physicians compared imaging findings. Results: Eight patients underwent FDG PET/CT and PSMA PET/CT images. In five patients, PSMA uptake was higher than FDG uptake. The highest PSMA uptake occurred in a giant cell recurrent sacral tumor of a 27-year-old male patient; the SUVs for PSMA and FDG were 100 and 16, respec- tively. A 58-year-old male patient with osteolytic metastasis from renal cell carcinoma in the right scapula presented PSMA uptake higher than FDG (SUVs = 40 and 11, respectively). A recurrent spin- dle cell neural tumor in the upper limb of a 69-year-old male presented PSMA uptake also higher than FDG (SUVs = 27 and 8, respectively). A myxofibrosarcoma mass in the distal right leg of a 61- year-old female presented higher PSMA uptake slightly higher than FDG uptake (SUVs = 18 and 10, respectively). Interestingly, two patients with chordomas had heterogeneous PSMA and FDG up- take. The PSMA PET/CT of a 65-year-old male patient presenting multiple metastases from chor- doma with soft tissue invasion showed uptake higher than FDG in all lesions; the highest SUV was a lesion in the right acetabulum: PSMA SUV = 32 and FDG SUV = 19. This patient presented PSMA-avid additional sites of metastases in mediastinal lymph nodes and the right hepatic lobe, while FDG uptake was minimal in these metastases. In contrast, an FDG PET/CT of a 54-year-old male with a large recurrent chordoma (30x24 cm mass) extending from the level of L4 to the proximal left thigh presented FDG uptake higher than PSMA uptake (SUVs = 31 and 9, respectively). Also, FDG uptake of two patients (52-year-old males) with desmoid tumors in the upper limb was higher than PSMA uptake, although uptake of both radiotracers was low: PSMA SUVs of 3 and 5, and FDG SUVs of 4 and 7. Conclusion: The study results show the potential advantage of using PSMA PET/CT and FDG PET/CT to provide additional information for monitoring patients and combining therapies, especially as PSMA PET/CT demonstrated more extensive disease. PSMA PET/CT has the advantage of the possi- bility of a Theranostic approach.

Keywords

• Musculoskeletal tumors
• PET FDG
• PET PSMA
• Theranostic