UTILITY OF 6- [18F]-L-FLUORO-L-3, 4-DIHYDROXYPHENYLALANINE POSITRON EMISSION TOMOGRAPHY-MAGNETIC RESONANCE IMAGING (18F-DOPA PET-MRI) METRICS AS A BIOMARKER FOR TREATMENT ASSESSMENT IN SARCOMA PATIENTS
Faculty and Abstracts
Purpose: To test the clinical utility of 18F-DOPA PET/MRI in the treatment management of high-grade soft tissue sarcoma patients by: 1) determining the correlation between post-treatment (pre-surgical) 18F-DOPA PET/MRI metrics and pathologic response, and 2) comparing changes in 18F-DOPA PET/MRI metrics pre- and post-radiotherapy (RT) treatment with pathologic response. We hypothesize that 18F-DOPA PET metrics (SUVmean, SUVmax, total metabolic tumor volume, tumor-to-normal tissue SUV, and/or histogram characteristics) are predictive of pathologic cell death following treatment. We hypothesize that changes on pre- and post-RT PET imaging are indicative of pathologic response, suggesting 18F-DOPA PET use as an early prognostic imaging biomarker.
Methodology: A total of 10 patients (age ≥ 18 years, minimum tumor diameter of 1 cm) with confirmed high grade soft tissue sarcoma receiving surgery at Mayo Clinic Florida with or without radiotherapy are eligible. All patients undergo an 18F-DOPA PET/MRI within 28 days prior to surgery. Five of those patients will also undergo an 18F-DOPA PET/MRI within 28 days of radiation therapy to evaluate uptake changes related to treatment response. All patients will be scanned on a 3T General Electric PET/MRI. Patients will be given an injected dose of 5 mCi. After 15 minutes, whole body PET images will be acquired. Simultaneous MR Dixon and ZTE sequences are used for attenuation correctio. 30 minutes post-FDOPA injection, dedicated MRI) in the regions of localized tumor is performed for 30 minutes. PET imaging metrics will be used to correlate with the pathological findings of percent necrosis and viable tumor.
Results: Four patients have been enrolled on this clinical trial (N=2 females, 2 males; Age range: 23-70 yrs). Two patients had a grade 3 myxofibrosarcoma (left scapula and right shoulder), one patient with a grade 3 undifferentiated pleomorphic sarcoma (left upper medial thigh), and one patient with a grade 2 alveolar soft part sarcoma (right upper posterior thigh). Three patients received a single pre-surgical PET, and one received both a pre-RT and pre-surgical PET. SUVmax for the two myxofibrosarcoma patients was 5.6 and 8.6 with 42.5% (57.5%) and 55% (45%) viable tumor (necrosis), respectively. The SUVmax for the grade 2 patient was 2.1 with >99% ( < 1%) viable tumor (necrosis). SUVmax for the other grade 3 patient was 5.0 pre-RT and reduced to 2.9 post-RT, with < 1% (0%) viable tumor (necrosis), >99% fibrosis/cystification.
Conclusions: We have demonstrated both technical and clinical feasibility using 18F-DOPA PET/MRI to image sarcoma tumors across anatomical areas. Our preliminary data shows a correlation with pathologic findings of necrosis/viable tumor within the surgical specimen. The SUVmax data might also have a dependency on tumor grade. This clinical trial is still in the early stages of data collection and analysis. Future analysis will include additional quantitative PET and MRI imaging metrics.
