Validation of a neck-thyroid phantom with small sizes of thyroid remnants using I-131 and I-123

Anthropomorphic phantoms are widely used in nuclear medicine for quality assurance and optimization of imaging techniques without exposing patients to radiation. They can be used in postsurgical SPECT/CT thyroid imaging to provide information about the presence and sizes of remnants and then to accurately determine the therapeutic doses for ablation. This study aims to validate a custom-made neck-thyroid phantom with thyroid remnants for SPECT/CT imaging. For the validation, the custom-made and a commercial phantom were used. The custom-made phantom consists of a hollow neck which encloses a trachea, an oesophagus, a cervical spine, and a removable section with two hollow cavities of 1.5 and 3 mL to simulate thyroid remnants. The RS542 commercial consists of a solid neck and a removable thyroid gland which was modified to enclose same sizes of remnants, at the same clinically relevance position, as in the custom-made phantom. SPECT/CT acquisitions were performed using various activities of ¹³¹I and I-123 in both phantoms. The SPECT sensitivity (counts/ (sec×activity)) for each remnant were measured. The counts in each remnant showed a linear correlation with activity in both phantoms. The measured sensitivity was comparable among the two phantoms in the whole range of activities. This custom-made phantom with small sizes of thyroid remnants, that can also simulate background activities, can be used to evaluate postsurgical thyroid SPECT/CT imaging. Acknowledgments: This study was co-funded by the European Regional Development Fund and the Republic of Cyprus through the Research and Innovation Foundation (author)