Finger doses due to68Ga-labelled pharmaceuticals in PET departments-results of a multi-centre pilot study.

INTRODUCTION: Although the use of68Ga has increased substantially in nuclear medicine over the last decade, there is limited information available on occupational exposure due to68Ga. The purpose of this study is to determine the occupational extremity exposure during the preparation, dispensing and administration of68Ga-labelled radiopharmaceuticals. METHOD: Workers in eight centres wore a ring dosimeter for all tasks involving68Ga-labelled radiopharmaceuticals for a minimum of one month. Additionally, the fingertip dose was monitored in two centres and the hand with the highest ring dose during68Ga procedures was also identified in one centre. RESULTS: The median normalised ring dose for68Ga procedures was found to be 0.25 mSv GBq-1(range 0.01-3.34). The normalised68Ga ring doses recorded in this study are similar to that found in the literature for18F. This study is consistent with previous findings that the highest extremity dose is found on the non-dominant hand. A limited sub study in two of the centres showed a median fingertip to base of the finger dose ratio of 4.3. Based on this median ratio, the extrapolated annual68Ga fingertip dose for 94% of the workers monitored in this study would be below Category B dose limit (150 mSv) and no worker would exceed Category A dose limit (500 mSv). CONCLUSION: When appropriate shielding and radiation protection practices are employed, the extremity dose due to68Ga is comparable to that of18F and is expected to be well below the regulatory limits for the majority of workers.

Extremity exposure of nuclear medicine workers: results from an EANM and EURADOS survey.

BACKGROUND: Extremity exposure during the handling of unsealed radioactive sources is a matter of concern for nuclear medicine workers. Next to 99mTc and 18F, other radiopharmaceuticals have seen an increase in their use over the last decade. However, limited information on their impact on extremity dose is available. This study aimed to gain insight into the status of extremity exposure and dose monitoring in Europe. METHODS: A survey was conducted at the end of 2020 among the European Association of Nuclear Medicine community. It contained 24 questions considering department characteristics, worker tasks, dosimeter use, typical worker extremity dose, department workload for selected radionuclides (99mTc, 18F, 68Ga, 177Lu, 90Y) and protective measures. RESULTS: A total of 106 replies were received, 92% of which were from Europe. About half of the respondents were from academic hospitals. Ninety-nine departments implement extremity dose monitoring for a total of 1335 workers. Most workers (95%) wear a ring dosimeter, generally on the non-dominant hand, and 44% on the index finger. Monthly doses were generally low (median values at different ring position: 0.4-1.8 mSv), although higher doses were reported (20.8-38.8 mSv). About 1/3 of workers performed the full task range (preparation, dispensing, and administration). Administration is associated with significantly lower extremity doses. Interestingly, no correlation between department workload and collective dose was found. The adoption of vial and syringe shielding, as well as distance tools, was common. The workers dispensing 99mTc without syringe shielding or PET nuclides without automated system received a significantly higher dose. Handling 68Ga, 177Lu and 90Y did not appear to have an impact on the reported doses. CONCLUSIONS: Protective measures play a significant role in lowering extremity doses, while department workload and more recently introduced radionuclides seem not to be major dose determinants.

Need for harmonisation of extremity dose monitoring in nuclear medicine: results of a survey amongst national dose registries in Europe.

Staff handling radiopharmaceuticals in nuclear medicine (NM) may receive significant extremity doses. Over the last decade in particular there has been an increase in NM procedures and new radiopharmaceuticals have been introduced. However, literature provides limited recent data on the exposure of the extremities. In addition, proper assessment of the equivalent dose to the skin can be difficult when applied to the fingertips. In order to gain insight in the actual exposure and to find out how European countries are dealing with monitoring of the extremities, a survey was performed amongst European regulatory authorities. The questions covered general aspects of the national dose registries (NDRs), the measured extremity doses and the practice of the monitoring of workers. The survey shows that extremity dosimetry is performed for about 25%-50% of the monitored workers in NM. Also, the recorded extremity doses in the NDRs are low (mean values 5-29 mSv yr-1) compared to the dose limit. Despite the recommendations that have been published in the last 10 years, few countries provide guidance on the wearing position of extremity dosemeters and the correction factor to estimate the maximum equivalent skin dose from the measured dose. This may lead to an underestimation of the maximum skin dose. Thermoluminescence ring dosemeters are widely used, but wrist dosemeters are also very common, even though the correlation of the measurement with the maximum skin dose is worse than for ring dosemeters. Furthermore, not all countries had a central registration of the extremity dose at the time the survey was performed.

Review of extremity dosimetry in nuclear medicine.

The exposure of the fingers is one of the major radiation protection concerns in nuclear medicine (NM). The purpose of this paper is to provide an overview of the exposure, dosimetry and protection of the extremities in NM. A wide range of reported finger doses were found in the literature. Historically, the highest finger doses are found at the fingertip in the preparation and dispensing of18F for diagnostic procedures and90Y for therapeutic procedures. Doses can be significantly reduced by following recommendations on source shielding, increasing distance and training. Additionally, important trends contributing to a lower dose to the fingers are the use of automated procedures (especially for positron emission tomography (PET)) and the use of prefilled syringes. On the other hand, the workload of PET procedures has substantially increased during the last ten years. In many cases, the accuracy of dose assessment is limited by the location of the dosimeter at the base of the finger and the maximum dose at the fingertip is underestimated (typical dose ratios between 1.4 and 7). It should also be noted that not all dosimeters are sensitive to low-energy beta particles and there is a risk for underestimation of the finger dose when the detector or its filter is too thick. While substantial information has been published on the most common procedures (using99mTc,18F and90Y), less information is available for more recent applications, such as the use of68Ga for PET imaging. Also, there is a need for continuous awareness with respect to contamination of the fingers, as this factor can contribute substantially to the finger dose.

A European survey on the regulatory status for the estimation of the effective dose and the equivalent dose to the lens of the eye when radiation protection garments are used.

Following the proposal of the ICRP for the reduction of the dose limit for the lens of the eye, which has been adopted by the International Atomic Energy Agency and the European Council, concerns have been raised about the implementation of proper dose monitoring methods as defined in national regulations, and about the harmonisation between European countries. The European Radiation Dosimetry Group organised a survey at the end of 2017, through a web questionnaire, regarding national dose monitoring regulations. The questions were related to: double dosimetry, algorithms for the estimation of the effective dose, methodology for the determination of the equivalent dose to the lens of the eye and structure of the national dose registry. The results showed that more than 50% of the countries that responded to the survey have legal requirements about the number and the position of dosemeters used for estimation of the effective dose when radiation protection garments are used. However, in only five out of 26 countries are there nationally approved algorithms for the estimation of the effective dose. In 14 out of 26 countries there is a legal requirement to estimate the dose to the lens of the eye. All of the responding countries use some kind of national database for storing individual monitoring data but in only 12 out of 26 countries are the estimated effective dose values stored. The personal dose equivalent at depth 3 mm is stored in the registry of only seven out of 26 countries. From the survey, performed just before the implementation of the European Basic Safety Standards Directive, it is concluded that national occupational exposure frameworks require intensive and immediate work under the coordination of the competent authorities to bring them into line with the latest basic safety standards and achieve harmonisation between European countries.

High dose rate and flattening filter free irradiation can be safely implemented in clinical practice.

PURPOSE: We hypothesize that flattening filter free (FFF) high dose rate irradiation will decrease cell survival in normal and cancer cells with more pronounced effects in DNA repair deficient cells. Additionally, we hypothesize that removal of the flattening filter will result in an enhanced relative biological effectiveness independent of the dose rate. MATERIALS AND METHODS: Clonogenic survival was assessed after exposure to dose rates of 4 or 24 Gy/min (FFF 10 megavolt [MV] photon beam) using a Varian TrueBeam accelerator. Additionally, cells were exposed to 4 Gy/min with or without flattening filter. Relative biological effectiveness estimations were performed comparing the different beam photon spectra. RESULTS: Cell survival in tumor and normal cell lines was not influenced by high dose rate irradiation. The intrinsic radiation sensitivity of DNA repair deficient cells was not affected by high dose rate compared to normal dose rate. Furthermore, the relative biological effectiveness was not significantly different from unity in any of the cell lines for both FFF and conventional flattened beam exposures. CONCLUSIONS: High dose rate irradiation did not affect long-term survival and DNA repair for cell lines of different tissues. This suggests that high dose rate does not influence treatment outcome or treatment toxicity and could be safely implemented in clinical routine.

Recommendations on detectors and quality control procedures for brachytherapy beta sources.

BACKGROUND AND PURPOSE: It is estimated that one third of the institutes applying clinical beta sources does not perform independent dosimetry. The Netherlands commission on radiation dosimetry (NCS) recently published recommended quality control procedures and detectors for the dosimetry of beta sources. The main issues of NCS Report 14 are summarized here. MATERIALS AND METHODS: A dosimetry survey was performed among 23 institutes in The Netherlands and Belgium. Well ionization chambers, a plastic scintillator, plane-parallel ionization chamber, diode and radiochromic film were used for determination of source strength (dose rate at reference distance) and uniformity of intravascular and ophthalmic sources. The source strength of multiple sources of each type was measured and compared with the source strength specified by the manufacturer. RESULTS: The standard deviation of the difference between measured and specified source strength was mostly about 3%, but varied between 0.8 and 15.8% depending on factors such as source type, detector, phantom and manufacturers calibration. The average non-uniformity was about 7% for intravascular sources and 20% for ophthalmic sources. It is estimated that the total relative standard uncertainty can be kept below +/-4% (1 sigma) with all detectors tested. Maximum deviations in source strength of 10% and a non-uniformity below 10% (intravascular) and 30% (ophthalmic) are recommended. CONCLUSIONS: Dosimetric and non-dosimetric quality control procedures on beta sources are recommended. They enable standardized measurements, including the determination of relative source strength and non-uniformity. Absolute calibrations depend on the future introduction of primary standards for clinical beta sources.