Objective To evaluate the influence of inappropriate position deviation on radioactive iodine uptake (RAIU),effective half-life (Teff) and the corresponding dose variances in patients suffering from Graves hyperthyroidism.Methods RAIU was examined in 20 patients with Graves hyperthyroidism (7 males,13 females,average age (46.60 ±9.55) years) 2,4,6,and 24 h after intake of the radioiodine capsule.A scintillation probe was positioned at the center of the inferior edge of the thyroid cartilage 25 cm away for 2 min,which was defined as the standard manipulation (test 1).Then,the probe was moved either 5 cm backward (test 2) or 5 cm higher (test 3) compared with test 1.Variants of RAIU,Teff as well as dose calculations were acquired by different combinations (CⅠ-Ⅸ) of 4 h and 24 h-RAIU,according to the above 3 manipulations (C Ⅰ-Ⅲ:test 1 for RAIU4 h,test 1,2,3 for RAIU24 h respectively ; C Ⅳ-Ⅵ:test 2 for RAIU4h,test 1,2,3 for RAIU24h respectively; CⅦ-Ⅸ:test 3 for RAIU4h,test 1,2,3 for RAIU24h respectively).Paired t test was used to compare the statistical differences between C H-Ⅸ to C Ⅰ.Results RAIU24 h of test 2 (68.08％ ± 7.88％) and test 3 (62.18％ ± 7.45％) were significantly lower than that of test 1 (78.05％ ± 8.31％ ;t =12.15,14.37,respectively,both P ＜ 0.01).Teffs of C Ⅱ (4.42 ± 0.73) d,CⅢ(3.76 ±0.53) d,CⅤ(5.59 ±0.46) d,CⅥ(4.47 ±0.44) d,CⅧ(5.94 ±0.54) d and CⅨ (5.45 ±0.66) d were significantly different from that of C Ⅰ (5.04 ±0.56) d which was defined as standard (t:3.86-13.64,all P ＜0.01).Among the 180 131I dose values calculated by different Teff and RAIU values induced from C Ⅰ-Ⅸ combinations,74.4％ (119/160) were over-calculated while 9.4％ (15/160) were under-calculated.Taking one patient as an example,the changes of RAIU24 h (decreased up to 26.0％) and the percentage of Teff deviation(66.9％,ranged from-47.5％ to 19.4％)led to an over-calculated 131 I dosage by as high as 129.8％ compared with CⅠ.Conclusions Incorrect positioning in RAIU detection could result in various false RAIU,Teff and 131I dose calculations.Such deviations could possibly exert an impact on the patients' therapeutic outcomes,thus influencing the efficacy of the iodine therapy.Optimization of RAIU positioning is essential for clinical practice to guarantee radioiodine dose management.