Absorbed dose to the thyroid of adults and children
due to I123, using MIRD dosimetry and MARINELLI
M.V. Vásqueza,b; C.E.Castilloa; P.W. Sáncheza; C.A. Cabreraa; E. Díazc;
J.A. Rocha a; L.Cespedesa; H.F. Floresa
a
Universidad Nacional de Trujillo, Trujillo-Perú
b
Universidad Cesar Vallejo (UCV), Trujillo-Perú
c
Universidad Rio Grande do Sul, Brasil
E-mail: marvva@hotmail.com
ABSTRACT
The absorbed dose to the thyroid gland is estimated through analysis of (organs) biokinetics of I-123
(iodine) .It uses the method MIRD, the Cristy-Eckerman representation for the organs of biokinetics of
adults, children of 15.10, 5, 1 years and newborns.The results show that the absorbed dose to the thyroid
due to emissions of I -123, are given by 2.95 mGy / MBq (4.637 mGy / MBq, 7.013 mGy / MBq, 15.47
mGy / MBq, 28.9 mGy / MBq) and 39.9 mGy / MBq, respectively; The corresponding dosimetric
contributions of organs that are part of its biokinetics (excluding the thyroid) is not significant in the
estimated dose.In the same way, using the formalism MARINELLI to estimate thyroid doses represented
by a sphere, for adults, children and newborn , the results show that they are not significantly different
from those reported by the formalism MIRD.
Keywords: dosimetry MIRD / MARINELLI, I-123 – iodide
1. INTRODUCTION
To estimate the absorbed dose in the thyroid of adults, children, and newborns during
uptake studies, it can be done through the analysis of (bodies) of the
radiopharmaceutical biokinetics I-123 (iodine).
Biokinetics organs: thyroid, small intestine, stomach, kidneys, bladder and other organs
(Spanish Society of Radio Pharmacy, 2013)
Similarly, to estimate the dose absorbed by the thyroid of adults, children, newborns,
can be used dosimetry MARINELLI which sees the thyroid gland with a spherical
representation.
2. MATERIALS AND METHODS
To estimate the dosimetric contributions organs biokinetics in the thyroid of adults,
children and newborns, we use the formalism MIRD, and the representation of CristyEckerman to these bodies. Medical Internal Radiation Dosimetry considered equations
(Spanish Society of Radio Pharmacy, 2013):
D fotones (tiroides )
A0


    k k (tiroides  i)   i
i 1  k

Dparticula (tiroide  tiroide )
A0
 [ E particle
 tiroide
mtiroide
rad / Ci
 E particle
 TB
mTB
] x 2,13
τTB = Total residence time of the body
mTB = Total body mass
The absorbed fractions, Φk (thyroid ← i) g -1, of “i" analyzed organs (kidneys, whole
body and your bladder), for photon energies "k" of I-123
were obtained from
ORNL/TM-8381/V2,V3,…,V7 (Cristy and K. Eckerman ,2013b).
Residence times of radiopharmaceuticals mentioned in each organ biokinetics, given in
Table 1, were obtained from the website (Health Physics Society, 2011) .
Table 1: Residence times (hours) and biokinetics of I-123 (Iodide),( (HPS, 2011)
Time
Resistence
Thyroid
Stomach
Small
intestine
Kidneys
Bladder
content.
Rest of
body
Newborn*
2,940
1,080
1,080
0,062
0,833
5,03
1 years
2,910
1,080
1,080
0,062
0,833
5,03
5 years
2,920
1,080
1,080
0,062
0,833
5,03
10 years
2,930
1,080
1,080
0,062
0,833
5,03
15 years
2,940
1,080
1,080
0,062
0,833
5,03
Adult
2,940
1,080
1,080
0,062
0,833
5,03
*They are the same as for an adult (Hedrick, 1987).
rad / Ci
 k  2,13 nk E k
(
rad  gm
) , represents average energy of the “k” photons emitted
Ci  hr
in the decay of I-123 , given in Table 2, were obtained from web page (Health Physics
Society, 2012).
Table 2: Data for nuclear emitted photons (MeV) of I-123 most significant (HPS,2012)
Ek
PHOTONS
nk /des
 k  2,13 n k E k
(
(Me V)
rad  gm
)
Ci  hr
0,1590
0,8330
0,28210
0,5290
0,0139
0,01570
0,0270
0,2460
0,01415
0,0275
0,4600
0,02690
0,0310
0,1600
0,01056
Gamma
Characteristic
Radiation
Eparticle (MeV/des.), represents the average energy of particles emitted by the I-123,
i.e., represents the electrons appearing in the decay processes for capturing and Auger
electrons are given in Table 3 and were obtained from web page (Health Physics
Society, 2012).
Table 3: Data for nuclear emitted particles (MeV) of I-123 most significant
Radionuclide (HPS,2012)
PARTICLES
Ek (MeV)
nk /des
nk Ek
( MeV / des )
0,1272
0,1360
0,01730
0,1540
0,0177
0,00270
0,1580
0,0035
0,00055
ELECTRON
0,0032
0,9400
0,00300
AUGER
0,0227
0,1235
0,00280
ELECTRONS
CONVERSION

E particle   nkEk
( MeV / des)
0,0205
0,0058
Mass values of the thyroid for adults, children and newborns, and the total body, given
in Table 4 were obtained from ORNL / TM-8381 / V1 (Cristy and Eckerman, 2013a).
To estimate the absorbed dose in the thyroid due to photons emitted by the I-123 is
determined according to Marinelli scheme (Quimby, Feitelberg and Gross, 1970):
0, 001   g  thy
Dfotones
(tiroide  tiroide) 
A0
m thy

thy
(rad / Ci)
, residence time of the gland ;  (tissue)  1 g .cm-3;
 (I-123) = 1,6 R mCi-1.h-1.
g (cm) is the average geometric factor for thyroid represented by spheres and radius r
is given by r = 3 π .where r 
3
3m
4
g ,values calculated for the thyroid gland adults, children and newborns, are presented
in Table 4.
For this formalism, the estimated absorbed dose to the thyroid gland due to particles
emitted by I-123 (iodide) can be expressed as (Michael and Stabin, 2013):
D
(
particula tiroide  tiroide
Ao
)
 E particle (
 thy
m thy
) x 2.13
rad / Ci
Table 4: Mass values for thyroid, and total body Cristy -Eckerman representation
(CRISTY, 1987a)
Newborn
1 year
5 years
Thyroid
mass (g)
1,29
1,78
Total body
(Kg)
3,6
4,99
g (cm)
10 years
15 years
adult
3,45
7,93
12,40
20,70
9,7
19,8
33,2
56,8
73,7
5,62
6,97
9,25
10,74
12,73
Using the methodology MIRD and Cristy-Eckerman representation for adult thyroid
gland, children and newborn, the study is to determine if the dose absorbed by the gland
due to I-123 (iodide) is significantly different from that reported by MARINELLI
formalism, when you use the sphere as glandular representation.
3. RESULTS AND DISCUSSIONS
Table 5: Absorbed dose to the thyroid of adults, children and newborn due to I-123
(iodide), Cristy-Eckerman representation and formalism MIRD (mGy / MBq)
Ages
emissions
D(T ← T)/Ao
D(T← i)/Ao*
Sub-total
Photons : γ + x
2,10 + 2,67
0,030
4,80
CE + e- Auger
27,00 + 8,10
-
35,10
Photons: γ + x
1,71 + 2,47
0,014
4,19
CE + e- Auger
19,25 + 5,45
-
24,70
Photons: γ + x
1,17 + 1,51
0,002
2,682
TOTAL
39,90
Newborn
28,90
1 year
15,472
5 year
CE + e- Auger
9,97 + 2,82
-
12,79
Photone: γ + x
0,66+0,76
0,003
1,423
CE + e- Auger
4,36+1,23
-
5,59
Photons: γ + x
0,504+0,53
0,0034
1,037
CE + e- Auger
2,80+0.80
_
3,60
Photons: γ + x
0,33 + 0,47
0,002
0,80
CE + e- Auger
1,65+0,50
7,013
10 year
4,637
15 year
2,95
adult
(*) i = all source organs except the thyroid
2,15
Table 6: Comparison of absorbed dose to the thyroid due to emissions of I-123, using
methods of MIRD and MARINELLI (mGy / MBq)
AGES
Newborn
1 year
5 years
10 years
15 years
adult
D (T  T ) D (T  i )

Ao
Ao
D(T  T )
Ao
MIRD
MARINELLI
Photons
4,80
4, 91
partícles
35,1
35,1
TOTAL
39,9
40,01
Photons
4,19
3,97
partícles
24,70
24,70
TOTAL
28,89
28,67
Photons
2,682
2,56
partícles
12,79
12,79
TOTAL
15,472
15,35
Photons
1,423
1,47
partícles
5,59
5,59
TOTAL
7,013
7,06
Photons
1,037
1,09
partícles
3,60
3,60
TOTAL
4,637
4,69
Photons
0,80
0,78
partícles
2,15
2,15
TOTAL
2,95
2,93
EMISSIONS
DOSE-RATIO
Marinelli /Mird
1,00
0,99
0,99
1,00
1,01
0,99
The results of absorbed dose to the thyroid of adults, children and newborn, show that:
(i)
The results of the MIRD dosimetry indicate that 99% of the total dose
absorbed by the gland of an adult, children and newborn corresponds to self-
dose. Dosimetric contributions corresponding to their organs biokinetics, is
less than 0.07%, ie negligible (Table 5).
(ii)
The results of dosimetry MARINELLI indicate that are not significantly
different from those obtained by the MIRD scheme (Table 6)
(iii)
The dosimetric contributions of particles that are emitted by I-123, are those
that contribute most to the total dose absorbed by the thyroid, amounts
varying from 73% (newborns) to 88% (adults).
(iv)
Depending on the type of radiopharmaceutical used and biokinetics, it will
be the importance of their contributions in the estimate of absorbed dose to
the thyroid of adults, children and newborns (Quimby, Feitelberg y Gross,
1970; Vásquez, Castillo et al, 2015).
4. CONCLUSION
Using the formalism MIRD and representation of Cristy-Eckerman thyroid adults,
children and newborn, it proves that the dosimetric contributions of the organs of the
biokinetics of I-123 (iodine), excluding the thyroid, are not significant in the estimated
dose. The total dose absorbed by the gland is self-dose. The reported results are not
significantly different from those found by the MARINELLI scheme for thyroid
represented by a sphere
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