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Macedonian Journal of Medical Sciences. 2011 Mar 15; 4(1):12-16.

doi:10.3889/MJMS.1857-5773.2011.0146

Basic Science

 

RADAR Calculated vs. TLD Effective Doses to Family Members of Thyroid Cancer Patients Treated with Iodine 131
 

Marina Zdraveska-Kocovska, Olivija Vaskova, Venjamin Majstorov

Institute of Pathophysiology and Nuclear Medicine “Akademik Isak S. Tadzer” - Faculty of Medicine, University “Ss. Kiril and Metodij”, Skopje, Republic of Macedonia

 

Abstract

 

 

Introduction: Patients who receive therapeutic amount of radioactive iodine 131 are significant sources of radiation to their family members, members of the public and others. The situation can be overcome by imposing restrictions on the behavior of the patient to minimize the effective dose to close relatives and not to exceed the proposed dose limits by the International Commission of Radiation Protection (ICRP) and Basic Safety Standards (BSS) from the International Atomic Energy Agency (IAEA).

Aim: The aim of this study was to evaluate effective dose to family members of thyroid cancer patients treated with radioiodine 131.

Material and Methods: We used thermoluminiscent dosimeters (TLD 100) and RADAR (Radiation Dose Assessment Resource) software for estimation of effective doses.

Results: The mean value of effective dose to relatives of thyroid cancer patients was 0.21 mSv. The estimated value of RADAR calculated effective doses for the distance of 0.25, 0.5 m, 1.0 m, 2.0 m were 17 mSv, 4.20 mSv, 1.00 mSv and 0.26 mSv respectively for administered activity of 3700 MBq.

Conclusion: Thyroid cancer patients should continue to be treated on in – patient basis to be sure that they will represent minimal radiation hazard for the people in their environment.

..................

Citation: Zdraveska-Kocovska M, Vaskova O, Majstorov V. RADAR Calculated vs. TLD Effective Doses to Family Members of Thyroid Cancer Patients Treated with Iodine 131. Maced J Med Sci. 2011 Mar 15; 4(1):12-16. doi.10.3889/MJMS.1957-5773.2011.0146.

Key words: thyroid cancer; relatives; radioiodine; TLD; RADAR software.

Correspondence: Marina Zdraveska Kocovska, medical physicist. Institute of Pathophysiology and Nuclear Medicine, Medical Faculty, Vodnjanska 17, 1000 Skopje, Republic of Macedonia. Phone: + 389 23 11 28 31; Fax: + 389 23 14 72 03; Mobile: + 389 71 21 35 73. E-mail: mzk2003@hotmail.com

Received: 25-Jun-2010; Revised: 29-Aug-2010; Accepted: 15-Sep-2010; Online first: 18-Jan-2011

Copyright: © 2011 Zdraveska-Kocovska M. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Competing Interests: The author have declared that no competing interests exist.

 

Introduction

 

The most frequently used radiopharmaceutical for treatment of thyroid diseases such as Thyroid Cancer and Hyperthyroidism is radioactive iodine 131. It has a very high success rate in treatment of patients with thyroid diseases and also it has proven to be a safe and a relatively inexpensive treatment modality. At Institute of Pathophysiology and Nuclear Medicine at the Faculty of Medicine in Skopje some 50 patients with thyroid carcinoma are treated with radioiodine 131 on in-patient basis each year. They stay three to four days in isolation ward, where every day medical physicist does the measurements of dose rate at different distances. The treatment renders the patient radioactive for a period of time. The patients, treated with radioiodine 131 represent a radiation hazard to other individuals such as hospital staff, the patient’s family and members of the public with whom the patient may come in contact. The situation can be overcome by imposing restrictions on the behavior of the patient, to minimize the dose to close relatives and other individuals.

In 1991 the International Commission on Radiological Protection has recommended a substantial reduction of doses for members of the public from 5 mSv to 1 mSv/y and proposed the concept of dose constraints as a process for optimization [1]. The Basic Safety Standards proposed dose constraint for public is 0.3 mSv per episode, for children is 1 mSv, adults up to 60 years old is 3 mSv and adults more than 60 years old dose constraint is 15 mSv [2]. The implementation of these guidelines differs among various countries, even in the same country differs between hospitals [3, 4]. Doses to relatives can be estimated from dose rates of the patient or measured with proper dosimeter. Also, there are several developed software’s which can be used for calculation of doses received from patients treated with unsealed radionuclides. In this study we used RADAR (Radiation Dose Assessment Resource) software available on web site and supported by the SNM (Society of Nuclear Medicine), Education and Research Foundation. The RADAR dose calculator performs dose calculations for release of radioactive nuclear medicine patients and dose from other related situations [5]. Although there is significant number of papers in the literature concerning the subject of doses received by family members of thyroid cancer patients we did not find any literature where RADAR dose calculator was used. Most of the published studies agree that provided recommendations are followed. Doses to all family members of thyroid cancer patients are below 1 mSv the proposed dose constraints by the ICRP and BSS [6].

The aim of this study is to investigate whether the restriction imposed on the lives of the patients treated with radioiodine 131 for thyroid cancer successfully maintains the dose to family members below the recommended limits proposed by the ICRP and the BSS Directive (96/29 EURATOM). The other purpose was to compare the measured TLD effective doses with RADAR calculated doses to family members of thyroid cancer patients treated with radioiodine 131.

 

Material and Methods

 

A total of sixty persons were included in the study. Thirty were thyroid cancer patients and the same number was patient’s relatives. They agreed to wear the TLD’s on the front of the torso for seven days. Twenty four family members were male and six were female. Their age varied from 28 years up to 73 years. Effective dose measurements were done with thermoluminiscent dosimeters model TLD 100 which contains hot pressed chips from lithium fluoride (LiF:Mg,Ti) with 3 mm2 square, encapsulated between two sheets of Teflon 10 mg/cm2 thick and mounted on an aluminium substrate with-bar code and also mounted within shielded filter holders (type 8814 Harshaw). Detection threshold of dosimetry system is 0.0054 mSv. TLD’s were most appropriate to estimate radiation because the amount of ionizing radiation is directly proportional to the effective dose [7]. Actually it was estimated Hp [10]. These types of dosimeters have photon energy response for gamma rays that ranges from (15 keV- 3MeV) (IEC 1066). The TLD Reader and Cards are calibrated on regular basis. The purpose of reader calibration is to maintain a consistent output from the Reader over a period of time based on a source in Second Standardize Dosimetry Laboratory (SSDL) - Cesium 137. The combined standard uncertainty of a dosimetry system is less than 15%. Control TLD was kept separately to measure the background. The background readings were subtracted from the readings of estimated effective doses to relative’s TLD’s.

The administered dose for treatment of Thyroid cancer patients ranged from 3700 MBq to 5550 MBq of 131I. Mean dose rate was 3539 MBq. Twenty six patients received 3700 MBq, two patients received 4440 MBq and two patients received 5550 MBq radioiodine 131. They were hospitalized three days after administration and the dose rate was measured every day at distance of 0.25 m, 0.5 m, 1.0 m and 2.0 m by medical physicist. The dose rate measurements were performed with calibrated survey meter “mini-rad” series 1000, Morgan. When the level of 8 µSv/h at 2 m was reached the patients were released from hospital. Upon discharge, patients were given radiation safety instructions for their further behavior with aim to minimize the transfer of radiation to persons coming in close contact with them especially children and pregnant woman. Their relatives wore the TLD and they were informed not to stay very close to the patient and if they do to reduce the time of staying. The TLD were read with an automatic calibrated TLD reader (Thermo Harshaw 6600 plus).

RADAR patient exposure radiation dose calculator was established on the internet to provide rapid, worldwide dissemination of important dose quantities and data. The program gives dose calculation to physicians, nurses, family members and others from patients who have been given radiopharmaceuticals. In this study RADAR was used in order to estimate effective doses at different distance to family members of thyroid cancer patients who received therapeutic amount of radioiodine 131. The program is designed to calculate total dose for certain exposure separately for thyroid cancer patients for infinite period of time. Besides estimated effective doses program gives the number of days for the same dose might be reached from natural background radiation. As variables we put given activity (MBq) and average distance (m) and we get the results for total dose estimated for given exposure. The calculation were done with values for occupancy factor - 0.25, for extra thyroidal fraction F1 - 0.95 and F2 thyroidal fraction was 0.05.Teff-1 – extra thyroidal was 0.32 days and Teff-2 thyroid was 7.23 days. These values were used as it was proposed in the program.

 

Results

 

The results for effective dose to relatives of the thyroid cancer patients treated with radioiodine 131 measured by TLD’s in most cases were below proposed dose constraint of 1 mSv. The range of effective dose varied from 0.02 mSv to 0.51 mSv. At three family members the TLD has shown value 0 mSv when the background was subtracted. The possible explanation was that these patients continued to be isolated from others after they had left the hospital. Table 1 presents effective doses to the relatives of thyroid cancer patients.

Table 1: Effective dose to family members of Thyroid cancer patients.

No.

mSv

Sex

Age (y)

1

0.05

m

28

2

0.00

m

35

3

0.00

m

26

4

0.27

f

38

5

0.00

m

46

6

0.16

m

35

7

0.02

f

50

8

0.43

m

35

9

0.32

f

33

10

0.23

f

73

11

0.31

m

32

12

0.25

m

70

13

0.17

f

60

14

0.20

m

44

15

0.15

m

40

16

0.40

m

40

17

0.51

m

70

18

0.08

m

40

19

0.43

m

40

20

0.06

m

41

21

0.33

f

60

22

0.02

m

41

23

0.15

m

61

24

0.20

m

65

25

0.41

m

40

26

0.17

m

38

27

0.23

m

56

28

0.37

m

60

29

0.02

m

58

30

0.35

m

48

Mean

0.21

 

 

The mean value of effective dose to relatives of thyroid cancer patients estimated with TLD was 0.21 mSv.

The Figure 1 presents effective doses to relatives of thyroid cancer patients versus proposed dose constraint by BSS for adults up to 60 years dose constraint of 3 mSv and 15 mSv for persons older than 60 years.The estimated effective doses to all family members of Thyroid Cancer patients were well below the recommended dose constraints proposed by ICRP of 1 mSv. At ten relatives were estimated values higher than 0.3 mSv (recommended dose limit for public per episode). This limit could be reached very easily. According Basic Safety Standards (para II-9) recommended actual values for dose constraint and dose limits shall not apply to comforters of patients who knowingly exposed while voluntarily helping patients during their treatment.

 


 

Figure 1: Effective dose to relatives of Thyroid cancer patients vs. Dose Constraint.

RADAR calculated dose for family members of Thyroid cancer patients

The results from RADAR calculated effective doses for family members of Thyroid cancer patients are given in Table 2. Besides estimated effective doses program gives the number of days for the same dose that might be reached from natural background radiation (Table 2).

Table 2: Calculated RADAR doses according given activity.

No.

Dose

MBq

0.25 m

0.50 m

1.00 m

2.00 m

mSv

backgr.

(day)

mSv

backgr.

(day)

mSv

backgr.

(day)

mSv

backgr.

(day)

1

3700

17.00

-

4.20

506

1.00

127

0.26

32

2

4440

20.00

-

5.00

608

1.20

152

0.31

38

3

5550

25.00

-

6.20

760

1.60

190

0.39

47

 

For the distance of 0.25 m, 0.5 m and 1.0 m the calculated doses by RADAR were higher than proposed dose limits, (17 mSv, 4.20 mSv and 1 mSv for activity of 3700 MBq respectively to distance), but for distance of 2.0 m calculated dose for administered activity of 3700 MBq was 0.26 mSv and it is very close to the mean measured dose by TLD (0.21 mSv). The results are presented on the given Figure 2.

 

Figure 2: Effective doses (TLD vs RADAR estimated values for 1.0 m and 2.0 m).

We might suppose that family member’s have stay at the suggested distance of more than 2.0 m and have reduced close contacts with the patient. The Figure 2 shows only the doses less than 2 mSv at distance of 1.0 m and 2.0 m. With dot line are shown the values of effective dose as estimated with TLD and in the most cases the values are overlapping with estimated RADAR values for 2.0 m.

 

Discussion

 

The use of TLD’s for estimation of effective dose to family members of patient treated with radioiodine 131 is easy to implement and it has been shown to be effective tool for dose assessment. The mean value of 0.21 mSv is less than proposed dose constraint of 0.3 mSv and recommended limit of 1 mSv. Thyroid carcinoma patients after three days of hospitalization and after release from hospital do not represent great radiation hazard to public or to their family members. From the practice very rare we have measured the dose rate of 8 µSv/h reached on second day staying at hospital. When it is measured we released them second day, with given written instructions. They should carefully follow given instruction for radiation protection for the next seven days to be sure that they will not impose radiation to others.

According RADAR calculator for thyroid cancer patient after three days of hospitalization, 0.5 m is safe distance to maintain the dose limit less than proposed 5 mSv. Also distance of 1.0 m is safe to maintain the dose limit less than 1 mSv. At the distance of 2.0 m for the exposure of 3700 MBq the estimated total amount of radiation that might be received is 0.26 mSv and is equivalent to a uniform whole body exposure that might have occurred after 32 days of exposure to natural background radiation. If the patient is administered 5550 MBq the estimated amount of radiation that someone might receive is 6.20 mSv for 0.5 m and 0.39 mSv for 2.0 m. For the distance of 0.25 m from the patient, the estimated doses are increasing substantially from 17 mSv up to 25 mSv. Doses to the relatives of thyroid cancer patients have been also reported from other authors [6, 7, 13, 14]. Their results were comparable to ours even the period of time of wearing the TLD was different. Culver and Dworkin [13] suggested that patients being treated for thyroid cancer who were released from the hospital when their body content reached < 1110 MBq of 131I were less of a hazard than patients treated for hyperthyroidism because the thyroid gland in hyperthyroidism retained a higher percent of the administered dose of radioiodine 131 longer. Barrington et al. found that the patients treated with radioiodine 131 for thyroid carcinoma travelling after treatment rarely present radiation hazard to other passengers if travel times are limited to a few hours [8].

In another study by Mathieu et al. [14] the dose measured with TLD’s was lower than 0.5 mSv in all partners of thyroid cancer patients. Generally the recommended dose limits are well met among family members of patients treated with iodine 131 for cancer. They suggest that dose constraint of 0.5 mSv should be complied with whenever possible.

Detailed instruction for patients and family members proposed by European Commission contain exact information for time and distance in different situations that the patients might come to.

We did not find any paper covering the calculated effective dose by RADAR dose rate calculator. Increasing the distance from the patient and reducing the time spent in close proximity with patient still remains one of the most important principles for radiation protection. With detailed given instructions to patients and their family members we could be sure that radioiodine therapy for thyroid carcinoma patients at our institution is performed on safe way.

 

Conclusion

Thyroid carcinoma patients receiving radioactive iodine for therapy should continue to be treated on in-patient basis. After release they should get written information on their further behavior for next seven days. They should follow the advices with aim to reduce the doses to their close family member. The distance of two meters from the patients is safe in order proposed dose limits not to be reached. RADAR is very useful software which can be easily implemented in daily routine practice in the field of radiation therapy. Even though the calculated doses were overestimated we found it as appropriate tool for fast estimation of dose to person who might come in close contact with thyroid carcinoma patients.

 

References

 

1. International Commission on Radiological Protection 94 Release of patients after therapy with unsealed radionuclides. J Valentine (ed) Elsevier Stockholm, 2004;34:19-20.

2. International Atomic Energy Agency, Basic Safety Standards for Protection against Ionizing Radiation and for the Safety of Radiation Sources, 1996.

3. Friedman MI, Ghesani M. Interactive software automates personalized radiation safety plans for Na131I therapy. Health Phys. 2002;83:S71-84.

4. De Santis DM, Chabot GE. An alternative method for the release criteria and calculation of total dose to another individual from a patient treated with a therapeutic dose of 131I. Health Phys. 2001;81:15-26.

5. RADAR Patient Exposure Radiation Dose Calculator-available from INTERNET-http://www.doseinfo-radar.com/RADAR-INT_NM calculator.

6. Monsieurs M, Thierens H, Dierckx RA et al. Real-life burden to relatives of patients treated with iodine – 131: a study in eight centers in Flanders (Belgium). Eur J Nucl Med. 1998; 25:1368-1376.

7. Jacobsen AP, Plato PA, Toeroek D. (1978), Contamination of the home environment by patients treated with iodine-131: initial result, Am J Public Health. 1978;68(3):225-230.

8. Barrington SF, Kettle AG, O’Doherty M. et al. Radiation dose rates from patients receiving iodine -131 therapy for carcinoma of the thyroid. Eur J Nucl Med. 1996;23(2):123-130.

9. European Commission on radiation Protection 97. Radiation Protection following iodine-131 therapy (exposure due to outpatient basis or discharged in-patients), Luxembourg, 1998, p 10.

10. de Klerk JM. 131I therapy: inpatient or outpatient? J Nucl Med. 2000;41(11):1876-8.

11. International Commission on Radiation Protection Publication 94: Release of patients after therapy with unsealed radionuclides. ICRP, Elsevier, Oxford 2005:pp.80.

12. International Atomic Energy Agency, Safety Reports Series No. 63 Release of Patients After Radionuclide Therapy, Vienna, 2009.

13. Culver CM, Dworkin HJ. Radiation safety considerations for post-iodine-131 hyperthyroid therapy. J Nucl Med. 1991;32:169-173.

14. Mathieu I, Caussin J, Smeesters P, Wambersie A, Beckers C. Recommended restrictions after 131I therapy: measured doses in family members. Health Phys. 1999;76(2):129-36.

 

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