Is eye lens dosimetry needed in nuclear medicine?

Determination of a reliable assessment for occupational eye lens dose in nuclear medicine

The most recent statement published by the International Commission on Radiological Protection describes a reduction in the maximum allowable occupational eye lens dose from 150 to 20 mSv/year (averaged over 5‐year periods). Exposing the eye lens to radiation is a concern for nuclear medicine staff who handle radionuclide tracers with various levels of photon energy. This study aimed to define the optimal dosimeter and means of measuring the amount of exposure to which the eye lens is exposed during a routine nuclear medicine practice. A RANDO human phantom attached to Glass Badge and Luminess Badge for body or neck, DOSIRIS and VISION for eyes, and nanoDot for body, neck, and eyes was exposed to ^99mTc, ¹²³I, and ¹⁸F radionuclides. Sealed syringe sources of each radionuclide were positioned 30 cm from the abdomen of the phantom. Estimated exposure based on measurement conditions (i.e., air kerma rate constants, conversion coefficient, distance, activity, and exposure time) was compared measured dose equivalent of each dosimeter. Differences in body, neck, and eye lens dosimeters were statistically analyzed. The 10‐mm dose equivalent significantly differed between the Glass Badge and Luminess Badge for the neck, but these were almost equivalent at the body. The 0.07‐mm dose equivalent for the nanoDot dosimeters was greatly overestimated compared to the estimated exposure of ^99mTc and ¹²³I radionuclides. Measured dose equivalents of exposure significantly differed between the body and eye lens dosimeters with respect to ¹⁸F. Although accurately measuring radiation exposure to the eye lenses of nuclear medicine staff is conventionally monitored using dosimeters worn on the chest or abdomen, eye lens dosimeters that provide a 3‐mm dose equivalent near the eye would be a more reliable means of assessing radiation doses in the mixed radiation environment of nuclear medicine.

Radiation doses to the eye lenses of radiologic technologists who assist patients undergoing computed tomography

The present study aimed to determine the amount of radiation exposure to the eye lenses of radiologic technologists while assisting patients undergoing computed tomography imaging and the effects of wearing lead glasses on dose reduction. Monthly radiation doses were collected for 12 months. Dose quantities at a depth of 3 mm (H_p(3)) were measured at the neck using personal optically stimulated luminescence (OSL) dosimeters. We also estimated H_p(3) as converted air kerma using small OSL dosimeters at the neck and at six positions on the lead glasses near the eyes. The total dose-length product at the time of patient assistance was 53,341 mGy·cm/y. The H_p(3) from the personal dosimeter was 9.13 mSv/y and the highest dose recorded by the small OSL dosimeters attached outside the lead glasses was 8.47 mSv/y. The lead glasses reduced the radiation exposure by ~ 60%.

A cost-effective way to reduce the equivalent eye lens dose fromYttrium-90 radiopharmaceuticals

PURPOSE

We analyzed the effect of the use of Eye Protective Equipment (EPE) and the best position to use individual dosimeters to estimate the eye lens radiation dose to a medical staff that works with yttrium-90.

METHODS

Three Alderson-Head-Phantoms were exposed to 58MBq of ⁹⁰Y for 24h, in two different experiments: (1) at different dosimeter placements and (2) with and without the use of EPE. The measurements were carried on by thermoluminescent technique.

RESULTS

Doses received by dosimeters on both lenses were more closely represented by the ones placed between the eyes than those on the temples, which underestimated the doses by a factor of 3. Also, the transmission factors showed that the EPE was able to reduce the H_p(3) values from about 78% to 92%.

CONCLUSIONS

This study demonstrated that the use of EPE can optimize the ⁹⁰Y eye lens dose. An individual dosimeter should be worn between the eyes for an appropriate estimate of this equivalent dose.

MEASUREMENT OF OPERATIONAL DOSIMETRY QUANTITIES FOR NUCLEAR MEDICINE STAFF

According to the ALARA principle, exposure to radiation should be reduced as low as reasonably achievable. This principle is very important in nuclear medicine (NM), and different investigations have been performed by establishing protocols and standards for staff protection. This study aims to measure the operational quantities, personal dose equivalent, Hp (10), Hp (0.07) and Hp (3) for NM staff in Shiraz hospitals, and comparison with dose limits. Two types of dosimeters, TLD-100 and GR-200, were used in this study. In the first step, the calibration of dosimeters was performed using different phantoms. Then, a group of dosimeters was prepared and used for 1 month on the heads, wrists and chests of the staff for measurement of Hp (3), Hp (0.07) and Hp (10), respectively. The obtained values of Hp (10) were compared with the results of their personal dosimetry, film badge. The results of this study show good consistency in the measurements using the two dosimeters.

Calibration of the LiF - thermoluminescent detectors used for personal dose equivalent Hp(3) assessment

AIMS

The issue of exposure of eye lenses of employees exposed to ionizing radiation is an interesting topic not only from the point of view of deterministic effects related to the occurrence of cataracts, but also dosimetric aspects, in particular the calibration of detectors in units enabling the assessment of eye lens exposure or personal dose equivalent Hp(3). The paper presents the idea of calibrating thermoluminescent detectors designed for the Hp(3) values measurement of gamma radiation, which the source is the process of annihilation of positrons emitted by the deoxyglucose marker - ¹⁸F radionuclide.

METHODS

The method was based on the value of air kerma Ka to Hp(3) conversion coefficients (Hp(3,0°)/Ka) developed as part of the ORAMED project. High-sensitivity thermoluminescent detectors (MCP-N) produced in Poland were used in the measurements. During the exposure of the detectors, a ¹³⁷Cs gamma radiation source (irradiator ¹³⁷Cs/⁶⁰Co) and a 20cm diameter cylinder filled with water were used.

RESULTS & CONCLUSIONS

The value of conversion coefficient Hp(3,0°)/Ka for energy 511 keV is 1.31Sv/Gy and the calibration factor is (3.46±0.03)·10^-4 mSv/N (N - number of counts). Verification of the value of the obtained coefficient carried out using a cylinder with a diameter of 20cm showed a difference of less than 2% in relation to the value obtained by the method described in this paper.

Demonstrating Compliance With Proposed Reduced Lens of Eye Dose Limits in Nuclear Medicine Settings

Based on ongoing research on ionizing radiation thresholds for cataracts, the International Commission on Radiological Protection has proposed new guidelines lowering the annual occupational lens of eye dose limit from 150 mSv to 20 mSv. The International Atomic Energy Agency has operationalized these new guidelines. Subsequently, national/regional radiation protection regulators are reviewing their lens of eye dose limits with an aim of moving towards the proposed new limits, resulting in licensees having to demonstrate compliance. In health care settings, fluoroscopic interventional practices generally have higher lens of eye doses and nuclear medicine settings generally have lower doses. A prospective cohort (n = 19) of nuclear medicine technologists wore dedicated lens of eye dosimeters for a 3 mo period synchronized with their body dosimeter schedules. The lens of eye dosimeters were validated to have a linear response in the anticipated dose ranges. The participants worked in a relatively high-volume nuclear medicine practice, which included general and cardiac, positron emission tomography/computed tomography, radiopharmacy, and cyclotron operations. The annualized dose ranges were 0.0-3.68 mSv (lens of eye) and 0.48-4.72 mSv (whole body). There was a good correlation between lens of eye and body dosimeter readings (R = 0.67). There were no significant differences in lens of eye dose by work type, worker sex, or side on which the dosimeter was worn. The findings should be generalizable to other similar practices, especially in North America, and should be sufficient to demonstrate regulatory compliance in nuclear medicine settings with the proposed new lens of eye dose limits.

68Ga-DOTA-TATE-a source of eye lens exposure for nuclear medicine department workers

INTRODUCTION

Obtaining ⁶⁸Ga-DOTA-TATE (a radioconjugate consisting of the somatostatin analogue tyrosine-3-octreotate (Tyr3-octreotate or TATE) labelled with the positron emission tomography tracer gallium ⁶⁸Ga via the macrocyclic chelating agent dodecanetetraacetic acid (DOTA)) is a complex process and, as with any radiopharmaceutical whose basis is a short-lived radionuclide generator, it is based on a sequence of procedures beginning from the ⁶⁸Ge/⁶⁸Ga generator elution, labelling ligands with a radioisotope, dispensing doses of ⁶⁸Ga-DOTA-TATE for patients and finally injection of the preparation to patients. The complexity of this process may contribute to an increased exposure of eye lenses of the staff who perform the above-mentioned procedures, which is especially important at a time when the dose limit on the lens of the eye is being reduced from 150 to 20 mSv yr^-1.

OBJECTIVE

The work presents the exposure of eye lenses of the personnel of a nuclear medicine department who prepare and inject ⁶⁸Ga-DOTA-TATE.

MATERIALS AND METHODS

Radiochemists and nurses were monitored by dosimetry measurements with thermoluminescent detectors (TLDs).

RESULTS

The values of Hp(3)/A-normalised personal eye dose equivalent recorded in the group of radiochemists during the procedure of dispensing the doses of ⁶⁸Ga-DOTA-TATE for patients exceeded the value of 274 μSv/GBq.

CONCLUSIONS

The estimated annual Hp(3) values may exceed 20 mSv, which is particularly important due to the fact that procedures using the ⁶⁸Ga radioactivity are only a small part of the daily professional activity of the staff, resulting from the performance of other procedures that require the use of other radioisotopes.

THYROID EXPOSURE DURING 18F-FDG PRODUCTION PROCEDURES

The production of radiopharmaceuticals for the needs of positron emission tomography (PET), in particular 18F-FDG, is a multi-step process performed most often by physicists and chemists. The monitoring of occupational exposure of staff employed in radiopharmaceutical production centres includes the measurement of the Hp(10) and Hp(0.07) values. Occupational exposure to ionising radiation means that the thyroid may be, among others, affected by the radiation field. This work analyses the exposure of the thyroid gland of employees of centres that produce the isotopes for PET, in particular fluorine-18. The analysis take into account the employment structure and work system of the discussed centres. Measurements were carried out by using high-sensitivity thermoluminescence detectors (MCP-N). The measurements covered 17 employees. Our results show that the estimated maximum annual thyroid gland exposure will not exceed 30 mSv.