The recommended oral dose for the average patient (70 kg) is 3.7 to 14.8 MBq (100-400 µCi). The lower part of the dosage range 3.7 MBq (100 µCi) is recommended for uptake studies alone, and the higher part 14.8 MBq (400 µCi) for thyroid imaging. The determination of I 123 concentration in the thyroid gland may be initiated at six hours after administering the dose and should be measured in accordance with standardized procedures.
The patient dose should be measured by a suitable radioactive calibration system immediately prior to administration. The capsules can be utilized up to thirty (30) hours after calibration time and date. Thereafter, discard the capsules in accordance with standard safety procedures. The user should wear waterproof gloves at all times when handling the capsules or container.
Radiation Dosimetry
The estimated absorbed radiation doses to several organs of an average patient (70 kg) from oral administration of the maximum dose of 14.8 MBq (400 µCi) of I 123 are shown in Table 4 for thyroid uptakes of 5, 15, and 25%. For comparison at these three values of thyroid uptake, the estimated radiation doses from doses of 3.7 MBq (100 µCi) I 131, also used as thyroid imaging agent, are also included.
Table 4 Radiation Dose Estimates as a Function of Maximum Thyroid Uptake for I 123* Sodium Iodide At Time of Calibration and Expiry Compared to I 131
*Concentration at Time of Calibration: 97% I 123, 2.9% I 125, 0.1% Te 121
Concentration at Time of Expiry: 87.2% I 123, 12.4% I 125, 0.4% Te 121
All Iodine Kinetics treated as in MIRD Dose Estimate Report 5. Bladder voiding interval, 4.8 hours.
Tellurium 121 dosimetry taken from ICRP 30.
Target Organ
Maximum
Thyroid
Uptake (%)
Estimated Radiation Absorbed Doses
I 123
mGy/14.8 MBq
(rads/400 µCi)
I 131
mGy/3.7 MBq
(rads/100 µCi)
TOC
TOE
Thyroid
5
25
(2.5)
75
(7.5)
260
(26)
15
77
(7.7)
230
(23)
780
(78)
25
130
(13)
410
(41)
1300
(130)
Liver
5
0.089
(0.0089)
0.13
(0.013)
0.16
(0.016)
15
0.10
(0.010)
0.18
(0.018)
0.28
(0.028)
25
0.11
(0.011)
0.24
(0.024)
0.41
(0.041)
Ovaries
5
0.18
(0.018)
0.19
(0.019)
0.18
(0.018)
15
0.17
(0.017)
0.18
(0.018)
0.18
(0.018)
25
0.16
(0.016)
0.18
(0.018)
0.17
(0.017)
Red Marrow
5
0.12
(0.012)
0.16
(0.016)
0.15
(0.015)
15
0.12
(0.012)
0.18
(0.018)
0.21
(0.021)
25
0.13
(0.013)
0.19
(0.019)
0.27
(0.027)
Stomach Wall
5
0.96
(0.096)
0.98
(0.098)
1.7
(0.17)
15
0.89
(0.089)
0.91
(0.091)
1.5
(0.15)
25
0.82
(0.082)
0.85
(0.085)
1.4
(0.14)
Small Intestine
5
0.70
(0.070)
0.71
(0.071)
1.2
(0.12)
15
0.65
(0.065)
0.67
(0.067)
1.1
(0.11)
25
0.60
(0.060)
0.62
(0.062)
0.99
(0.099)
Testes
5
0.076
(0.0076)
0.089
(0.0089)
0.12
(0.012)
15
0.072
(0.0072)
0.087
(0.0087)
0.12
(0.012)
25
0.068
(0.0068)
0.085
(0.0085)
0.12
(0.012)
Bladder
5
1.7
(0.17)
1.7
(0.17)
2.9
(0.29)
15
1.6
(0.16)
1.6
(0.16)
2.7
(0.27)
25
1.4
(0.14)
1.5
(0.15)
2.4
(0.24)
Skeleton
5
0.11
(0.011)
0.16
(0.016)
0.12
(0.012)
15
0.12
(0.012)
0.18
(0.018)
0.18
(0.018)
25
0.14
(0.014)
0.21
(0.021)
0.24
(0.024)
Total Body
5
0.11
(0.011)
0.16
(0.016)
0.24
(0.024)
15
0.14
(0.014)
0.25
(0.025)
0.47
(0.047)
25
0.17
(0.017)
0.35
(0.035)
0.70
(0.070)
