Occupational radiation exposure of health professionals and cancer risk assessment for Lithuanian nuclear medicine workers

https://doi.org/10.1016/j.envres.2020.109144Get rights and content

Highlights

  • A pool of 2059 doses of occupationally exposed nuclear medicine workers has been reconstructed and investigated.

  • Additional performance of PET/CT examinations does not increase the doses to nuclear medicine staff significantly.

  • Exposure doses measured at ring position are 2–3 times lower than doses to fingertips.

  • Radiation risk for the development of thyroid cancer is higher for female nuclear medicine staff.

Abstract

Background

Reconstruction and analysis of low doses received by the occupationally exposed medical radiation workers, especially nuclear medicine staff dealing with radioisotopes may significantly contribute to the understanding of radiation impact on individuals, assess and predict radiation related risks for the development of cancer or other specific diseases.

Methods

A pool of 2059 annual effective doses corresponding to 272 job's positions occupied by nuclear medicine and radiology workers for a certain time period over 26 years in five Lithuanian hospitals was investigated in order to analyze the occupational exposure tendencies to medical staff. Requested data, measured in terms of whole body dose, personal dose equivalent Hp(10), was obtained from the National Register of Sources of Ionizing Radiation and Occupational Exposure. Considering that nuclear medicine staff is dealing with open sources/radioisotopes, doses to extremities, Hp(0.07), were measured using thermoluminescent dosimeters (TLD) of LiF:Mg, Ti type. Lifetime risk estimations for the development of specific cancer (thyroid cancer and leukemia) for exposed radiation workers were performed using risk models included in BEIR VII report (BEIR VII, 2006). The conservative assessment of the thyroid exposure was performed using RadRAT 4.1.1 tool.

Results

Doses to radiology technologists and radiology nurses were found to be highest over the years. However, their annual doses never exceeded dose limit of 20 mSv and were following the same decreasing tendency as the doses of other personnel. There was no increase of doses to nuclear medicine staff observed after installation of two new PET/CT machines, indicating increased radiation protection culture and application of relevant technical and protective measures by the staff. Measured fingertip doses were 2–3 times higher than the hand doses measured with TLD ring and were dependent on the type and frequency of the nuclear medicine examination procedure and on the type and activity of isotopes used for examination.

Conclusions

For the first time, retrospective dose evaluation for the cohort of medical radiation workers was performed in the country. It enabled estimation of lifetime attributable risk for the development of two cancer types: thyroid and leukemia cancer among occupationally exposed medical radiation staff. Projected risk was low, ~10−5, however it was found that the risk of thyroid cancer for female staff was 5.7 times higher than for the males. Obtained results will be used for the predictive assessment of possible radiation induced health effects to occupationally exposed medical radiation workers.

Introduction

Different physical, biological, chemical and other occupational risks of health professionals can alter according to the profession, the work itself and the unit of the hospital, and must be assessed centrally taking into account employee's working history, working environment and conditions as well as possible interactions and impacts of different risks (Ulutasdemir and Tanir, 2017). Ionizing radiation is one of the most important physical hazard, which may lead to the development of radiation induced cancer (e.g. leukemia and other circulatory diseases, skin, brain, thyroid, breast cancer) or other non-communicable diseases of medical radiation workers (Bernier et al., 2018; Ko et al., 2017; Wang et al., 2016; Azizova et al., 2018; Kitahara et al., 2018; Seo et al., 2018, Cardis et al., 2005, Yoshinaga et al., 2004). A new study on the assessment of cancer and other disease risks in U.S radiologic technologists (No. NCT02911155 (2016–2022) is still ongoing. The increased interest to radiation induced health effects of occupationally exposed medical workers clearly indicates that there is an urgent need to expand and upgrade available limited information on the average annual and time-trend doses from occupational radiation exposures. More dose-related data are needed to characterize organ-specific doses that could later be used to quantify lifetime risks for specific radiation-related disease outcomes, either directly through subsequent follow-up or indirectly through risk projection methods (Lee et al., 2018). Such studies may help to optimize standardized protocols for radiologic procedures, indicate the adequacy of currently used radiation protection measures for medical radiation workers and yield valuable insights on cancer risks that are associated with chronic radiation exposure. Since medical radiation workers are routinely exposed to the low doses due to the daily's activities their doses are monitored and stored. The investigation of these doses provides reliable complimentary information on radiation impact on human health to the dosimetry data from surveys of chronically exposed workers (after accidents) or data derived from environmental studies (McLean et al., 2017; Davesne et al., 2018; Magnusson et al., 2007).

Personnel working in nuclear medicine (NM) department is potentially experiencing the highest levels of radiation exposure relative to other medical radiation workers (Drozdovitch et al., 2014; Mettler et al., 2009) due to the fact that they are handling unsealed/open radiation sources, preparing and manipulating radiopharmaceuticals, and are exposed externally and internally (via possible inhalation of radioisotopes and wound). It should be noted, that the field of nuclear medicine has expanded rapidly since its inception in the mid-20th century. Improvement of imaging technologies (combined modalities like positron emission tomography-computed tomography, PET/CT, molecular imaging) and application of the new and emerging radioisotopes have generally reduced patient's exposure to radiation. However, the cumulative doses to nuclear medicine staff are expected to have increased due to the growing frequency of the performed nuclear medicine procedures and less used lead aprons that in fact, are less effective in protecting of workers, especially during PET/CT examinations, as compared to other radiation-related procedures (Kitahara et al., 2015). This may put workers at higher risk for cancers and other health problems that are related to radiation.

There is currently very little information about radiation-related risks associated with performing nuclear medicine procedures due, in part, to limited information on occupational doses associated with current nuclear medicine practices. The last survey on doses of the exposed nuclear medicine workers was reported in 2008 (UNSCEAR, 2008). Moreover, while estimation of doses received by different tissues and organs of patients exposed to radionuclide radiation during diagnostic examination or treatment is a part of the nuclear medicine procedure, occupationally received doses to individual organs/tissues are rarely estimated for medical personnel. In general, estimation of radiation doses for nuclear medicine personnel is performed for compliance purposes only. There are only very few cases when organ's doses to medical personnel are reconstructed. The data are usually used for the purpose of epidemiologic studies in order to estimate relationship between radiation dose and radiation induced health risks (Sigurdson et al., 2003; Simon et al., 2006, Simon, 2011; Gilbert, 2009).

Dose reconstruction for nuclear medicine department personnel presents unique challenges for a variety of reasons, including: (1) radiation doses to medical staff are low; (2) doses cannot be estimated with the same dose coefficients as for patients, who typically undergo specific diagnostic radiologic examinations according to established imaging protocols or are treated using specific radionuclides; (3) personnel monitoring data has to be carefully interpreted to give credible organ doses that properly account numerous assumptions about working and exposure conditions, also related to the involvement of the new technologies (IAEA, 2018 SSG-46).

The main radiation induced reactions in biological tissues are described by deterministic and stochastic effects that depend on irradiation dose (ICRP Publication 118:, 2012, Hamada and Fujimichi, 2014). High dose of ionizing radiation may cause detrimental or even acute health effects (deterministic effects) that are not pre-determined, but observed, when radiation incidents or accidents occur. Due to the evidence of biological injury, high dose impact on humans and dose evaluation methods are well established. Stochastic effects are incidental and have exposure related probabilistic character. Stochastic effects are low dose effects without occurrence of clinical symptoms in irradiated individuals and having highly reduced detection possibility for blood changes, thus radiation sensitivity, under the threshold dose of 500 mSv. Based on this, a lot of debates among scientists are ongoing, whether the low doses have any impact on human health (Calabrese and O’Connor, 2014; Burgio et al., 2018). However, everybody agrees, that radiation induced cancer risk exists. BEIR VII, UNSCEAR, ICRP risk models evaluate Lifetime Attributable Risk (LAR) of radiation induced cancer and fatal cancer as a function of absorbed dose received by organ or tissue of the exposed person. It is known, that in BEIR VII Life Attribute Risk for all induced cancers is estimated as 0.012% per mSv and for lethal all types of cancers - 0.006% per mSv; while accordingly in ICRP model radiation induced cancer risk is estimated as 0.017% per mSv and risk of cancer mortality – 0.004% per mSv. Performing this study we have followed the statements laid down in the of BEIR VII report (BEIR VII, 2006), where the risks of ionizing radiation exposure for cancer incidence rates as well as mortality were analyzed and estimated, reaffirming all previous conclusions that every (even the lowest) exposure to radiation produces a corresponding increase in cancer risk. BEIR VII statements are based on the results taken from a pooled analysis of studies of radiation workers, who were chronically exposed to low radiation doses in United States, Canada, United Kingdom, Italy, Central Europe countries Gilbert, 2001). Also direct epidemiological evidence from human populations indicating the increase of the risk of some cancers due to radiation exposure was taken into account (Brenner et al., 2003). It was shown (Gilbert, 2009), that increased radiation dose doesn't increase the severity of the cancer but increases the likelihood of cancer induction. BEIR VII risk assessment model was also applied by World Health Organization (WHO) for the estimation of health risks caused by the nuclear accident in Fukushima using preliminary estimated doses (WHO World Health Organization Report, 2013). It should be noted that the Linear no-Threshold (LNT) model was assumed by default for radiation induced cancer risk assessment, however many unsolved problems related to evaluation of biological effects produced by low level radiation were still left. These problems are worth of investigation, since due to the nuclear accidents in Chernobyl and Fukushima significant part of population remains chronically exposed to the low dose level. Since occupationally exposed workers are permanently under dose monitoring program the results of investigation of low doses received by staff during handling of radioactive substances in nuclear medicine department may contribute to the improvement of radiation protection and safety level in nuclear medicine department and also serve for the broader understanding of radiation induced long-term radiobiological effects and contribute to the further development of radiation risk assessment models.

The aim of this study was to analyze the dynamics of radiation doses received by occupationally exposed medical radiation workers in Lithuania during the last 26 years, to evaluate the doses to corresponding organs (hand/skin, thyroid) that are mostly affected by radiation when nuclear medicine staff is working with radioisotopes and to assess the life attributable health risk of the development of cancer and other specific diseases for the occupationally exposed staff.

Section snippets

Materials and methods

Individual whole-body doses from external exposure to various groups of medical radiation workers including staff from the nuclear medicine departments in five largest Lithuanian hospitals have been analyzed using data provided by Lithuanian National Register of Sources of Ionizing Radiation and Occupational Exposure (Register). Following personal data security restrictions, the numbers H1 to H5 were assigned to each of five hospitals and depersonalized dose data of medical radiation workers

Overall evaluation of doses to occupationally exposed radiation medicine workers

A pool of 2059 individual annual effective doses of occupationally exposed radiation medicine staff (272 persons) measured in terms of Hp(10) was analyzed. The total number of different hospital related job's positions taken from Register was 22. Particular numbers of employees/numbers of dose records during the whole period of 26 years (1992–2017) were as follows: cardiologists - 6/22 (starting from 2013), radio-onco-therapists - 28/368, radiologists - 39/261, doctors-residents - 11/29,

Conclusions

Retrospective evaluation of doses of 272 occupationally exposed radiation medicine workers during the period of 1992–2017 has been performed with a special focus to doses of nuclear medicine staff employed at five largest Lithuanian hospitals. Data was taken from The Lithuanian National Register of Sources of Ionizing Radiation and Occupational Exposure (total number of measurements - 2059).

Doses to 22 different job positions classified into four groups according to the assigned and performed

Declaration of interest

None.

Funding sources

This project is a part of the EU-COST action, CA 15129 (DiMoPEx), which is supported by the EU Framework Program Horizon 2020.

CRediT authorship contribution statement

D. Adliene: Conceptualization, Investigation, Supervision, Validation, Writing - review & editing. B. Griciene: Formal analysis, Methodology, Writing - original draft. K. Skovorodko: Data curation, Investigation, Writing - original draft. J. Laurikaitiene: Formal analysis, Investigation, Writing - original draft. J. Puiso: Data curation, Formal analysis, Writing - original draft.

Ackowledgements

The authors are grateful to Radiation Protection Centre of Lithuania for providing the data on occupationally exposed medical workers in Lithuania from State Register of sources of ionizing radiation and occupational exposure.

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