DOES LOSS OF 131I COUNTS NEED CORRECTION IN GAMMA-CAMERA IMAGING IN CHILDREN AND YOUNG ADULTS IN POST-THERAPEUTIC SCANS? COMPARISON OF PHANTOM VERSUS PATIENT STUDY.

This study aimed to verify whether there is whole-body (WB) count loss due to dead time of gamma camera when high amount of 131I is administered to patients. Planar views of a phantom containing 5751 MBq of 131I were acquired at 24-h intervals for 68 d. Eighty-two patients ≤21 y old were given diagnostic activity (74 MBq) followed by therapeutic activity (1110-5772 MBq). WB scans of patients were acquired at 2 h after diagnostic and therapeutic activity administration. Count loss in patients and phantom were compared. In phantom, there was no count loss up to 139 MBq. At maximum activity of 5751 MBq 131I, the loss was 46%. In patients, the average WB count loss was insignificant after the administration of therapeutic activity. Count loss due to dead time in phantom differed significantly from patient results that can probably be explained by the distribution of activity over a large area in vivo.

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