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ORIGINAL ARTICLE
Year : 2018  |  Volume : 14  |  Issue : 6  |  Page : 1361-1365

Analysis of the caregiver effective dose during I-131 therapy of thyroid


1 Department of Medical Radiation, Engineering Faculty, Central Tehran Branch, Islamic Azad University, Tehran, Iran
2 Reactor School, Nuclear Science and Technology Research Institute, Tehran, Iran

Date of Web Publication28-Nov-2018

Correspondence Address:
Yaser Kasesaz
Atomic Energy Organization of Iran, Tehran
Iran
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0973-1482.199382

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 > Abstract 


Aims: The main objective of the present research is to analyze the caregiver effective dose during I-131 therapy of thyroid in some different situations using MCNP4C Monte Carlo code.
Patients and Methods: Two separate whole body Medical Internal Radiation Dosimetry (MIRD) phantoms have been defined simultaneously in a single Monte Carlo N-Particle (MCNP) input file as the patient and the caregiver. Two different groups of irradiation situations have been assumed for the caregiver related to the patient, (1) both the patient and the caregiver are standing and (2) the patient is lying in the bed while the caregiver is standing beside the patient.
Results: The results show that the caregiver effective dose is highly dependent on the position of the caregiver related to the patient. When the patient is lying on the bed and the caregiver is standing beside the patient near the head of the patient, the effective dose of caregiver will be the maximum value.
Conclusions: Although the maximum effective dose (0.2 mSv) is smaller than the allowed value for caregivers (5 mSv for each treatment), the final results of this research indicate the importance of caregiver position in close contact with the patient.

Keywords: Caregiver effective dose, I-131, MCNP4C, MIRD phantom, thyroid


How to cite this article:
Taghvaee S, Kasesaz Y, Barough MS. Analysis of the caregiver effective dose during I-131 therapy of thyroid. J Can Res Ther 2018;14:1361-5

How to cite this URL:
Taghvaee S, Kasesaz Y, Barough MS. Analysis of the caregiver effective dose during I-131 therapy of thyroid. J Can Res Ther [serial online] 2018 [cited 2019 Sep 16];14:1361-5. Available from: http://www.cancerjournal.net/text.asp?2018/14/6/1361/199382




 > Introduction Top


The I-131 is the most used radioisotope in nuclear medicine. It is used to treat hyperthyroidism and thyroid cancer. The I-131 activity is administered in the range of 100–300 mCi.[1] Although the patient is instructed to keep a certain distance from the family members for several days after hospital discharge,[2] there may be some conditions that someone spend a period of time in close contact with the patient. In this case, one of the main concerns of those who are in contact with the patient (medical staff, caregiver, family, etc.) during radiotherapy is about the radiation dose and they would like to know the radiation risk in close contact with the patient. The main objective of the present research is to analyze the caregiver effective dose during I-131 therapy of thyroid in some different situations using MCNP4C Monte Carlo code.[3] To do this, two separate whole body MIRD phantoms[4] have been defined simultaneously in a single MCNP input file as the patient and caregiver. The thyroid of the patient has been defined as the radiation source and then the organ-absorbed dose and the whole body effective dose of the caregiver have been calculated. Seven different irradiation situations have been analyzed. The details of the modeling and calculations as well as results are described below.


 > Patients And Methods Top


The patient/caregiver model

As mentioned above, two separate whole body MIRD phantoms have been used simultaneously as the patient and the caregiver. The MIRD phantom is composed of three major sections: (1) an elliptical cylinder representing the trunk and arms, (2) two truncated circular cones representing the legs and feet, and (3) an elliptical cylinder capped by a half ellipsoid representing the head, placed on the top of a circular cylinder representing the neck. The phantom has 70 kg weight and 170 cm height. [Figure 1] shows the view of the MIRD phantom. To analyze the effect of the caregiver gender, all calculations have been done for both male and female phantoms. The radiation source was the thyroid of the patient that consists of the I-131.
Figure 1: The view of the MIRD phantom modeled in MCNP4C

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Irradiation situations

Two different groups of irradiation situations have been assumed for the caregiver related to the patient:

  1. Both the patient and caregiver are standing. This group consists of four different situations which are shown in [Figure 2]a
  2. The patient is lying on the bed while the caregiver is standing beside the patient. This group consists of three different situations which are shown in [Figure 2]b.
Figure 2: Two different groups of irradiation situations: (a) Both the patient and caregiver are standing. (b) The patient is lying on the bed while the caregiver is standing

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For each of these seven positions, the distance between the patient and caregiver has been changed from the minimum distance up to 300 cm.

In case of irradiation time, it has been considered that the caregiver spend 1 h/day in contact with the patient during 8 days after the intake of I-131.

Dose calculation

To calculate the organ-absorbed dose in a specific duration time, the following equation has been used:



where, F6 is the MCNP tally result in unit of MeV/g, C = 1.6e-10 to convert the unit of F6 result to Gy (J/kg), f is percentage uptake of I-131 by thyroid (3.8%), Iγ is the branching ratio of gamma decay (81%), A0 is the maximum I-131 activity (150 mCi), λ is the decay constant of I-131, and t is the time after I-131 ingestion. is the absorbed dose per source particle (PSP). This parameter is the time-independent parameter which has been defined to compare the absorbed and effective dose related to the different irradiation situations.

The average gamma-absorbed dose was determined using the F6 MCNP cards for all the desired organs.

According to ICRP 103,[5] the protection quantities to be used are the equivalent dose in organs and the effective dose. The equivalent dose is defined as:



where, DT, R is the average absorbed dose due to radiation of type R in the volume of a specific organ T and wR is the radiation-weighting factor. In this case, R refers to the gamma radiation and wR is equal to 1 that it means that HT = DT. According to ICRP 60, the effective dose E is defined as:



where, wT is the weighting factor for organ or tissue T and Epsp has been defined same as parameter. These protection quantities are calculated for the organs of interest in radiation protection for which ICRP 103[5] recommends organ-weighting factors as shown in [Table 1].
Table 1: Tissue-weighting factor

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 > Results Top


[Table 2] shows the absorbed dose of some selected organs PSP . As seen, the value of is highly dependent on the caregiver positions. In all organs, the minimum value of is related to the position D and the maximum value is related to positions A (lungs, thyroid, and breast) and B (liver, gonads, and bone marrow).
Table 2: of some selected organs (Gy/source particle)

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[Figure 3] presents the whole body effective dose PSP (Epsp) related to the different caregiver positions. It shows that the caregiver position has a significant effect on the effective dose. As seen, the minimum value of the effective dose is related to the position D whereas the maximum value is related to positions A and B. It is also seen that the effective dose of female caregiver is higher than the male because of the breast tissue factor.
Figure 3: The whole body effective dose per source particle (Epsp) related to the different caregiver positions

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[Figure 4] shows Epsp versus distance from the patient for different situations. As expected by increasing the distance, Epsp is reduced.
Figure 4: The Epsp versus distance from the patient for different situations

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[Table 3] presents the calculated effective dose, a situation in which the caregiver was in contact with the patient for 1 h/day during 8 days after the intake of I-131. It shows that after 8 days, the maximum caregiver effective dose is about 0.2 mSv in position B and 0.16 mSv in position A. It also shows that the minimum effective dose is about 2 μSv related to position D.
Table 3: Whole body effective dose during 8 days after intake for 1 h/day (mSv)

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 > Discussion Top


The caregiver effective dose during I-131 therapy of thyroid has been calculated in different situations. The results show that:

  1. The caregiver effective dose is highly dependent on the position of the caregiver related to the patient
  2. When the patient is lying on the bed and the caregiver is standing beside the patient near the head of the patient (position B), the effective dose of caregiver will be the maximum value
  3. When the patient is lying on the bed and the caregiver is standing beside the patient near the legs of the patient (position D), the effective dose of caregiver will be the minimum value
  4. When both the patient and the caregiver are standing, the maximum caregiver effective dose will be related to the position A
  5. The ratio between the maximum effective dose (position B) and minimum effective dose (position D) is about 100 which reveals that the caregiver should not stand in the (position B).


Although the maximum effective dose (0.2 mSv) is smaller than the allowed value for caregivers (5 mSv for each treatment),[6] the final results of this research indicate the importance of caregiver position in close contact with the patient.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
 > References Top

1.
Willegaignon J, Malvestiti LF, Guimarães MI, Sapienza MT, Endo IS, Neto GC, et al. 131I effective half-life (Teff) for patients with thyroid cancer. Health Phys 2006;91:119-22.  Back to cited text no. 1
    
2.
ICRP, Release of Patients after Therapy with Unsealed Radionuclides. ICRP Publication 94. Ann ICRP 2004:34.  Back to cited text no. 2
    
3.
Briesmeister JE. MCNP – A General Monte Carlo N-Particle Transport. USA: Los Alamos National Laboratory; 1986.  Back to cited text no. 3
    
4.
Krstic D, Nikezic D. Input files with ORNL-mathematical phantoms of the human body for MCNP-4B. Comput Phys Commun 2007;176:33-7.  Back to cited text no. 4
    
5.
The 2007 recommendations of the international commission on radiological protection. ICRP publication 103. Ann ICRP 2007;37:1-332.  Back to cited text no. 5
    
6.
NRC, Release of patients administered radioactive materials. NRC Publication, Regulatory Guide 8.39, Washington DC, 1997  Back to cited text no. 6
    


    Figures

  [Figure 1], [Figure 2], [Figure 3], [Figure 4]
 
 
    Tables

  [Table 1], [Table 2], [Table 3]



 

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