Effect of Personalized Approach to CT Scan Length on Radiation Dose in Parathyroid SPECT/CT.

Parathyroid SPECT/CT is the standard examination for localization of hyperfunctioning parathyroid tissue before surgery for hyperparathyroidism. The effective dose (ED) delivered by CT comprises approximately one third of the radiation dose in this examination. Parathyroid SPECT/CT typically includes 1 CT covering the mediastinum because of the risk of ectopic adenomas. This study investigates whether the use of personalized CT (pCT) on the basis of SPECT images can reduce scan length and CT-derived ED, while maintaining the ability to detect ectopic adenomas, compared with full field-of-view (FOV) SPECT/CT. Methods: Patients with hyperparathyroidism who were referred for a clinical parathyroid SPECT/CT between May 2023 and June 2024 were prospectively included. Two observers (a technologist and junior physician) retrospectively determined pCT based on the non-attenuation-corrected SPECT images. The reduction in CT scan lengths compared with those of standard CT examinations was calculated. In a subgroup of patients, the reduction in ED was calculated. The detectability of ectopic adenomas was analyzed using imaging data from the full FOV SPECT/CT as the reference standard. Results: In total, 113 patients were included in the study. The standard examination found that 82 patients had at least 1 suspected lesion. Scan length was reduced by 60%-66% using pCT. No ectopic adenomas were missed on pCT. Subgroup analysis showed comparable reductions in CT scan length and CT-derived ED. Conclusion: Median CT scan length and median CT-derived ED was reduced by 60% when pCT was used for parathyroid SPECT/CT. pCT was implemented with minimal delay between SPECT and CT.