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:
[email protected]
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
5. REFERENCES
CRISTY, M. y ECKERMAN, K. Specific absorbed fractions of energy at various ages from internal photons Sources. Oak Ridge, TN: ORNL/TM-8381 /V1. 1987a. CRISTY, M. y ECKERMAN, K. Specific absorbed fractions of energy at various ages from internal photons Sources. Oak Ridge, TN: ORNL/TM-8381 / V2,…,V7. 1987b
HEDRICK, W.R. and MILAVICKAS, L.R. Reevaluation of the Newborn Thyroid Dose from Radioiodines. J. Nucl. Med., 28, 1208-1209. 1987. HEALTH PHYSICS SOCIETY. Kinetic Models Used as the Basic for the Dose Estimates.
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