comparison of whole body 131iodine scan results in four, seven and nine days after radioiodine therapy of differentiated thyroid cancer

Introduction: finding optimum time of post ablation whole body iodine scan in patients with differentiated thyroid cancer(dtc) treated with i131.material and methods: 20 patients with dtc, who were treated with i131 underwent post ablation whole body iodine scan (wbis) in days 4, 7 and 9 after treatment. a dual head gamma camera (ecam, siemens) equipped with high energy parallel hole collimator was used for imaging. the images were acquired with 7cm/min and stored in a 1024 ×256 matrix. results: 3 patients had negative wbis in all three sets of imaging and 17 patients had postsurgical thyroid remnants on all 3 scans. on days 4 and 7 we detected 11 patients with cervical lymph node metastases while on day 9 only 9 patients showed cervical lymph node metastases.(p=0.135)on all 3 sets of images, we encountered 4 patients with mediastinal lymph node metastases and 1 patient with bone metastasis. in addition, all 3 sets of images detected lung metastases in three patients. the total number of affected foci did not have any statistical differences in whole body scan of day 4, 7 and 9. (p = 0.083)conclusion: according to the radiation safety hazards for staff and technicians of nuclear medicine department and lack of difference in scan findings between 4 and 7 days after rai, scanning the dtc patients in the day 7 after rai administration , is more practicable, with less probability of missing the sites of involvement. performing whole body iodine scans after 1 week is not recommended.