Determining the Artificial Influence Factors for Quality Assessment of Personal Radiation Dosimetry Services

doi:10.21203/rs.3.rs-1767206/v1

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Determining the Artificial Influence Factors for Quality Assessment of Personal Radiation Dosimetry Services

https://doi.org/10.21203/rs.3.rs-1767206/v1

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This study was to determine the artificial factors considered for the measurement accuracy of personal dosimeter in dosimetry services under current performance test criteria. The investigation included management information questionnaire, on-site visit and blind test. The blind test with random selected personal badge was used in inter-comparison of eight dosimetry services, and the test results followed ANSI/HPS N13.11 criteria. This study also analyzed the measurement deviations if they felt in the criteria of ICRP 75 or not. One-way ANOVA tests were used to analyze the significant difference of the measurement deviations in different dosimetry services, irradiation categories, and years of use. Simple linear-regression test was performed for the significance of the prediction model between measurement deviations (category I, category II deep, and category II shallow) and readout frequencies. All visited dosimetry services followed the proper statue of basic management and passed the performance check of the tolerance level. There had significant differences of measurement deviation in different dosimetry services and irradiation categories but no significant difference in years of use. There was no significance in the linear-regression model between measurement deviation and badge readout frequencies. Based on the regular calibration of the personal dosimeter, the deviation of the measured value is mainly affected by different dosimetry services and irradiation categories; and there shows no significant influence by years of use and readout frequency.

International Atomic Energy Agency (ICRP) has emphasized that the radiation staff’s occupational dose should consider the as low as reasonably achievable (ALARA) principle. It is essential to monitor the personal radiation dose to ensure a reasonable effective dose limit for radiation workers. In report No.103 of the International Commission on Radiological Protection (ICRP), personal dose monitoring should consider deep individual dose, H_p(10), and shallow individual dose, H_p(0.07) [1]. The integrity of personal dose monitoring requires basic management, practical implementation, and dose record-keeping by a qualified dosimetry service [2–5] The measurement accuracy of personal dosimeters is a critical issue. Thus, the dosimetry services should establish criteria for measurement accuracy [6].

In the United States, measurement accuracy refers to the American National Standards Institute and The Health Physics Society (ANSI/HPS) N13 series specification for the evaluation of tolerance level on personal dosimeter measurement performance [7, 8]. In Europe, the European Radiation Dosimetry Group (EURADOS) conducts routine intercomparison for dosimetry services within multiple countries using the measurement accuracy criteria in each country [9–11]. International Atomic Energy Agency (IAEA) also performs comparative studies of dosimetry services in various countries and establishes acceptance limits concerning the deviation between measurement and true irradiation value in ICRP reports [12–15]. Each dosimetry service sends personal dose badges to the National Radiation Standard Laboratory (NRSL) for irradiation following the radiation source category; then returns the badges to the original facilities for reading and reporting the personal radiation dose for evaluation. The previous studies related to personal dosimeter measurement accuracy had major discussion on the acceptance comparison between each dosimetry service under current criteria [16, 17]. However, it is a lack of discussion on forwarding analysis of the artificial factor, like years of use and readout frequency, and whether potentially effecting on the measurement accuracy.

This paper investigated management information of dosimetry services, including qualification recognition, workspace configuration, personnel dose badges, and readout equipment information. The surveyor conducted the blind test on-site [18, 19], visiting each dosimetry service to obtain personal dose badges randomly and sending them to NRSL for irradiation. Later, NRSL sent the badges back to the facilities where they originated to gauge the measurement dose under current criteria [20, 21]. Then, the analysis of the influence significance by the artificial factor (dosimetry service, irradiation category, years of use and readout frequency) on the dose deviation of the personnel dosimeter was performed. The results of this study could determine the artificial factors considered for the measurement accuracy constancy of personal dosimeter in dosimetry services, thereby certifying the quality assurance reinforcement of personal dose monitoring of radiation workers.

2.1. Questionnaire Investigation

This study sent the questionnaire to all eight dosimetry services in Taiwan. The questionnaire was designed with Google form (Google LLC, USA). It contained the following questions about personal dose badge information: type of dosimeter, years of use, numbers, readout equipment information, and dose record keeping.

2.2. On-site Visit

The on-site visit was conducted in each dosimetry service. Following the environment condition listed in ANSI/HPS N13.11 [22], the visit examined working space, radiation shielding, environmental control (temperature and humidity), fire alarm system, and document storing space. This study used the MiniTRACE CSDF survey meter (Saphymo SAS, Germany) to measure the environmental dose rate in visited facility space.

2.3. Blind Test

Each dosimetry service had a random selection of twenty-eight personal dose badges in total, and it was divided into four groups. Each group included six badges for irradiation and one for background calibration. After badges were selected and collected, the badges were sealed with a stamp in one package and sent to NRSL for standard source irradiation. This study employed category I (accidental photon) and category II (general photon) source for irradiation following ANSI/HPS N13.11. The irradiated personal dose badges were mailed back to the original facilities. The badges must be used to measure the radiation dose readings within three days after the facility receives the package.

The personal dose badge measurement performance was based on ANSI/HPS N13.11 with performance index Pi. Pi could be obtained by:

P _i = [H_i’-H_i] / H_i (1)

Where H_i’ is the measurement value reported by the dosimetry service, and H_i is the irradiation value reported by NRSL. With the Pi of each badge, the bias, B, could be obtained by:

$$B=\frac{\sum _{i=1}^{n}{P}_{i}}{n}$$

Where n is the number of irradiated badges, the Pi and B are used for standard deviation, S, which is obtained by:

$$S=\sqrt{\frac{\sum _{i=1}^{n}{({P}_{i}-B)}^{2}}{n-1}}$$

Finally, the badge measurement performance is defined by:

B ² + S² ≤ L² (4)

Where the L is tolerance level, for category I, L is set to be 0.24. For category II, L is set to be 0.3. This study also separated the irradiated badges into four groups by the years of use, including less than five years, 5 to 10 years, 10 to 15 years, and more than 15 years. Then, the re-calculation of measurement performance was done on the four different time groups.

2.4. Measurement Deviation

2.4.1. Deviation Analysis of Irradiated Badge

This study also calculated the measurement deviation of the irradiated badge. The measurement deviation could be obtained by:

$$\text{D}\text{e}\text{v}\text{i}\text{a}\text{t}\text{i}\text{o}\text{n}=\frac{{H}_{m}-{H}_{t}}{{H}_{t}} \times 100\%$$

Where H_m is the measurement value reported by the dosimetry service, H_t is the irradiation value reported by NRSL. The acceptance level of measurement deviation is based on ICRP report No.75 with the upper and lower limit called ‘trumpet curve’ [23, 24]. The limit is defined by:

$\text{U}\text{p}\text{p}\text{e}\text{r} \text{l}\text{i}\text{m}\text{i}\text{t} \text{f}\text{o}\text{r} \frac{{H}_{m}}{{H}_{t}}=1.5\left(1+\frac{{H}_{O}}{2{H}_{O}+{H}_{t}}\right)$ (6 − 1)

$$\text{L}\text{o}\text{w}\text{e}\text{r} \text{l}\text{i}\text{m}\text{i}\text{t} \text{f}\text{o}\text{r} \frac{{H}_{m}}{{H}_{t}}=\frac{1}{1.5}\left(1-\frac{2{H}_{O}}{{H}_{O}+{H}_{t}}\right)$$

6-2

Where H_O is the recording level, it is 0.2 mSv for a general whole-body dosimeter. In this study, the measurement deviation should be checked against the 1.5 and 1/1.5 criteria.

2.4.2. Statistical Methods for Deviation Analysis

One-way ANOVA tests were used to analyze the significant difference of measurement deviation in different dosimetry services, irradiation categories, and years of use. A simple linear-regression test was used to analyze the significance of regression coefficient, R, in the prediction model between measurement deviation (category I, category II deep, and category II shallow) and badge readout frequencies [25]. The readout frequencies were separated into five types of ‘group bins’ for the linear-regression test, including 10, 25, 50, 100, and 150 times in each bin. Data analyses were conducted by IBM SPSS Statistics 24 (IBM, USA). Statistical significance was hypothesized at 0.05.

3.1. Questionnaire Information

Table 1 shows the management information of eight dosimetry services, including badge information (producer, model, type, place of production, and numbers of facility use) and readout equipment information (model and numbers of facility use). Seven agencies used thermoluminescent dosimeter (TLD), and one service used optical stimulated luminescence dosimeter (OSLD). Each facility has at least two readout equipment for use. Figure 1 shows the proportion of personal badges within the four years of use groups, which are 8.70% (< 5 years), 31.69% (5–10 years), 30.81% (10–15 years), and 28.80% (> 15 years) respectively.

Table 1

The information of dosimetry services within eight dosimetry services in Taiwan.
Producer	Badge Information				Readout Equipment Information
Producer	Model	Type	Place of Production	Numbers of Lab. Use	Model	Numbers of Lab. Use
Thermo Scientific	Harshaw 8814	TLD	USA	4	6600 PLUS 8800 PLUS	3 2
Panasonic	UD-802	TLD	USA / Japan	2	UD-716 UD-7900M	2 1
RADOS	Whole Body	TLD	Germany	1	RE-2000	1
Landauer	UD-874A	OSLD	USA	1	Reader 200	1
Abbreviations: TLD: thermoluminescence dosimeter, OSLD༚optically stimulated luminescence dosimeter.

3.2. On-site Visit

All visited dosimetry services in this study followed the environment condition listed in ANSI/HPS N13.11, including proper workspace, radiation shielding, environmental control (temperature and humidity), fire alarm system, and document storing space. The environmental dose rate in all dosimetry service workspaces was less than 0.5 µSv/h on average. All dosimetry services had established record-keeping for backup verification for dose abnormality events.

3.3. Blind Test

Table 2 shows the result of the blind test corresponding to categories I and II within each dosimetry service. For category I which irradiated with Cs-137, all eight dosimetry services had passed the performance check (L² = 0.056). For category II which irradiated with M150, all eight dosimetry services also had passed the performance check (L² = 0.03). Table 3 shows the results of tolerance level re-calculation corresponding to four years of use groups. The B² + S² values for each interval still appear within the tolerances of the ANSI/HPS N13.11 specification for categories I and II.

Table 2

The blind test results corresponded to eight dosimetry services, including accidental (category I) and general photon (category II deep and shallow).
Participant	B² + S² Value			Pass
Participant	I	II, Deep	II, Shallow	Pass
A	0.007	0.028	0.028	Yes
B	0.002	0.015	0.003	Yes
C	0.004	0.007	0.018	Yes
D	0.007	0.007	0.010	Yes
E	0.005	0.013	0.068	Yes
F	0.004	0.003	0.001	Yes
G	0.013	0.020	0.008	Yes
H	0.008	0.018	0.012	Yes

Table 3

The blind test result corresponded to each years of use group in this study.
Age Interval	B² + S²			Pass
Age Interval	I	II, Deep	II, Shallow	Pass
y < 5	0.007	0.016	0.040	Yes
5 ≦ y < 10	0.007	0.024	0.034	Yes
10 ≦ y < 15	0.008	0.026	0.043	Yes
y ≧ 15	0.004	0.030	0.023	Yes

3.4. Measurement Deviation Analysis

Figure 2 shows the readout frequency corresponding to years of use for the selected badges. Approximately half of the selected badges (59.61%) had been used over ten years. The average readout frequency of the chosen badges was 143 times. Figure 3 shows the measurement deviation corresponding to years of use for the irradiated badges. The average deviations corresponding to three categories (category I, category II deep, and category II shallow) were 6.08%, 9.49%, and 10.41% respectively. Figure 4 shows the measurement deviation corresponding to the readout frequency for the irradiated badges. The overall range of deviation was from − 10.00–29.17%. The result of the One-way ANOVA test showed there had a significant difference in measurement deviation in: different dosimetry services (p < 0.0001) and irradiation categories (p = 0.016). There had no significant difference in years of use (p = 0.498).

Table 4 shows the result of the linear-regression test. When the readout frequency was used as the prediction model factor of measurement deviation, all readout frequency groupings’ R values had no significance in all group bins for three irradiation categories.

Table 4

The result of linear-regression between the frequency of readout procedure and dose deviation within three irradiation categories.
Group Bin of Readout Procedures^†	I		II, Deep		II, Shallow
Group Bin of Readout Procedures^†	R	p-value	R	p-value	R	p-value
10	0.040	0.817	0.275	0.105	0.245	0.149
25	0.003	0.985	0.253	0.137	0.233	0.172
50	0.008	0.962	0.269	0.113	0.264	0.120
100	0.016	0.927	0.260	0.126	0.298	0.077
150	0.105	0.542	0.208	0.224	0.193	0.258
^† The group of readout procedure was based on how many times of readout procedures which was chosen for one bin.

The total number of personal dose badges was about 160 thousand. It was sufficient for personal dose monitoring of radiation workers (about three times as much as the number of workers) [26]. There were more than 90% of in-used personal dose badges used over five years. Also, there were more than 25% of badges over 15 years.

The random selection of badges was proportionally based on the years of usage information offered by each dosimetry service. Thus, it could be sure that the proportion of new and old selected badges was appropriate. The measurement deviations of the irradiated badges corresponding to category I and category II deep were within the 1.5 and 1/1.5 upper/lower limits. However, the deviations of category II deep were larger than those of category I. It was due to the badge filter correction for the energy dependence of the dosimeter material. This characteristic had more influence on the uncertainty of the radiation energy below 500 keV [27]. The dose of category II shallow was calculated from that of category II deep by the conversion factor [27, 28]. Thus, the deviation uncertainty would be further higher than the category II deep dose.

The lattice stability of TLD would be affected by the readout process, thereby it would cause an increase in measurement deviation [29, 30]. However, there was no significance in the prediction model when the readout frequency was the factor of linear-regression. This was due to the regular calibration of badges performed by each dosimetry service. Based on the calibration factor, such as effective correlation factor/coefficient (ECF or ECC), the dosimetry service routinely excludes the badges that did not meet the calibration criteria. Thus, the measurement deviation had no longer highly related to the readout frequency. Furthermore, the R values in category II were higher than those in category I. This showed that the potential correlation for general level dose could be higher than that for accidental level dose. The conversion of measurement value in category II should be more careful. According to the result of linear-regression for category II shallow in this study, it is recommended to establish the measurement stability check for general level dose for the personal badges that have readout frequency over 100 times.

The significant difference in measurement deviations was impacted by the calibration process of each dosimetry service and the irradiation source type of badges. It is necessary for the lead organizer to carry on blind tests regularly or from time to time for taking reference of overall personal dose monitoring quality assurance.

This study investigated the information of dosimetry services. The number of personal badges was sufficient for personal dose monitoring of radiation workers. The results of the bling test showed that the measurement performance of personal badges passed the tolerance level of criteria under random selection mode. Based on the regular calibration of the personal dosimeter, the deviation of the measured value is mainly affected by different dosimetry services and irradiation categories; and there shows no significant influence by years of use and readout frequency. This could determine the artificial factors considered for the measurement accuracy constancy of personal dosimeter in dosimetry services, and reinforce the stability of personal dose monitoring to reach the ALARA principle mentioned by ICRP.

Availability of Data and Materials

The datasets generated and/or analyzed during the current study are not publicly available due [protection of the privacy data for each dosimetry facility] but are available from the corresponding author on reasonable request.

Acknowledgments

We appreciated to the dosimetry services for the cooperation in this study.

Author contributions

Chen-Ju Feng performed the questionnaire, on-site visit, data analysis and manuscript writing. Yi-Hui Huang helped in contact with the dosimetry services. Chien-Hau Chu provided the technical support on blind test. Ke-Yu Lien and Yu-Chieh Wang provided support on-site visit. Shih-Ming Hsu and Chin-Hui Wu reviewed the manuscript.

Funding

This work was supported by the Atomic Energy Commission, New Taipei City, Taiwan, Republic of China [AEC10904022L] and [AEC11012048].

Declarations of interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

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No competing interests reported.

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You are reading this latest preprint version

Determining the Artificial Influence Factors for Quality Assessment of Personal Radiation Dosimetry Services

Status:

Version 1

Abstract

Figures

1. Introduction

2. Materials And Methods

2.1. Questionnaire Investigation

2.2. On-site Visit

2.3. Blind Test

2.4. Measurement Deviation

2.4.1. Deviation Analysis of Irradiated Badge

2.4.2. Statistical Methods for Deviation Analysis

3. Results

3.1. Questionnaire Information

3.2. On-site Visit

3.3. Blind Test

3.4. Measurement Deviation Analysis

4. Discussions

5. Conclusion

Declarations

References

Additional Declarations

Status:

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