Abstract
Introduction: Integrin antagonist carbamate (IAC) – a newer αvβ3 integrin antagonist peptidomimetic molecule in the pipeline, has made the molecular imaging of tumour angiogenesis amenable. The study aims to investigate the biodistribution, clinical efficacy of 68Ga DOTAGA-IAC PET/CT in the detection of radioiodine refractory differentiated thyroid carcinoma (RAIR-DTC), to compare its diagnostic performance with the most commonly used imaging tool, 18F-FDG PET/CT.
Materials and methods: This prospective pilot study included RAIR-DTC patients who underwent whole-body 18F-FDG-PET/CT followed by 68Ga-DOTAGA-IAC PET/CT. For each patient, using organ specific circular regions of interest (ROIs) were evaluated in 16 anatomical structures on 68Ga-DOTAGA-IAC PET/CT to find out the biodistribution. A five-point grading system was proposed for the radiotracer uptake on 68Ga-DOTAGA-IAC PET/CT. Abnormal, non-physiologic radiotracer uptake (grade II and higher-grade lesions showing tracer uptake more than the mediastinal bloodpool) at a site congruous with disease activity was considered positive finding. The imaging findings of both the PET/CT were interpreted and quantitative parameters like SUVmax, MTV and TLG were obtained and statistically analyzed.
Results: For the biodistribution, maximum physiological tracer uptake was identified in the kidneys followed by spleen. 18F-FDG PET/CT detected 97 lesions (excluding the lung nodules) in 30 patients, majority of them being nodal lesions (73.2%) followed by skeletal lesions (15.5%). 68Ga-DOTAGA-IAC PET/CT detected 34 lesions (lung nodules were not taken into consideration similar to 18F-FDG PET/CT) in 14 patients. Out of the 34 lesions, 50% were nodal lesions. Few of the analysed patients had multiple grade lesions, with 20% of them having coexisting higher grade lesions (grade II and higher lesions) consistent with disease activity on 68Ga-DOTAGA-IAC PET/CT. The median SUVmax values of the lesions at all sites and volumetric parameters like median total MTV and TLG on FDG PET/CT outperformed IAC PET/CT.
Conclusion: Angiogenesis imaging with 68Ga-DOTAGA-IAC PET/CT appears to be inferior in the detection of lesions in patients with RAIR-DTC compared to 18F-FDG PET/CT, retaining the domination of FDG PET/CT imaging in clinical practice.