A Radiotheranostic Model for Thyroid Cancer Management

3106 Objectives: Functional imaging optimization and standardization are critical to patient individualized treatment and for continuity of care when records are transferred between institutions. Based on radiotheranostic principles we have developed a procedural model for acquisition of high-quality diagnostic radioiodine (131-I)imaging (Dx scan) for guiding therapeutic I-131 administration. This model can be used for developing a Thyroid Cancer Radiotheranostic program at most institutions. Methods: Planar whole-body scan and static neck and chest images are acquired in anterior and posterior projections at 24 hours after oral administration of 1-2 mCi (37-74 MBq) 131-I, followed by routine SPECT/CT imaging with an axial field of view extending from the skull base to the diaphragm. All abnormal activity foci seen on planar scans outside the neck and chest are also evaluated with SPECT/CT. Imaging is performed on a hybrid dual-head gamma camera with an inline CT scanner equipped with parallel-hole, high-energy collimators, using a 20% energy window set at 364 keV. The table speed for the whole-body images is 10 cm/min. Static images are acquired for 20 minutes using a 256 x 256 matrix. SPECT images were acquired in 64 projections (30 s/stop), with a noncircular orbit over 360 degrees using a 128 x 128 matrix. Tomographic images are reconstructed using high-sensitivity 3D OSEM iterative reconstruction (8 iterations, 4 subsets) and CT-based attenuation correction. CT imaging parameters are as follows: 130 kVp, 80 mAs, 3-mm collimation, and 0.8 pitch. CT reconstruction was performed at 5-mm slice thickness into a 512 x 512 matrix. Dx scan is reviewed for identification of regional and/or distant metastases and the decision for I-131 therapy and the prescribed I-131 activity is determined based on all available information (histopathology, stimulated thyroglobulin, and Dx scan findings). Post-therapy (post-Rx) whole-body scans and static neck and chest images are obtained at 2 -5 days after therapeutic I-131 administration in all patients and the results are correlated with the Dx scan results to assess for any additional findings. For post-Rx scan acquisition the table speed is increased at 30 cm/min for whole body imaging and static planar views of the neck and chest are acquired for 5 min. When additional activity foci are detected on post-Rx scans as compared to Dx scans (7-10% cases) SPECT/CT imaging using the same parameters the same as Dx scans is performed for full characterization. This diagnostic and post-therapy imaging protocol can be adapted for both adjuvant and for dosimetry-guided I-131 therapies. Results: Change in clinical management occurred in approx. 30% cases (1) based on Dx scan information, which detected regional metastases in 35% of patients and distant metastases in 8% of patients. (2). Conclusions: Optimization and standardization of imaging acquisition parameters for diagnostic I-131 planar and SPECT/CT imaging are important for obtaining high quality scans that help guide therapeutic I-131 administration. References:1. Avram AM, Esfandiari NH, Wong KK. Preablation 131-I scans with SPECT/CT contribute to thyroid cancer risk stratification and 131-I therapy planning. J Clin Endocrinol Metab. 2015;100(5):1895-902.2. Avram AM, Fig LM, Frey KA, Gross MD, Wong KK. Preablation 131-I scans with SPECT/CT in postoperative thyroid cancer patients: what is the impact on staging? J Clin Endocrinol Metab. 2013;98(3):1163-71.