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
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.
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.
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 mm 2
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.
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.
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.
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