Exposure of medical personnel to radiation during radionuclide therapy practices

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 (using^99mTc,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.

ICRP Publication 140: Radiological Protection in Therapy with Radiopharmaceuticals

Radiopharmaceuticals are increasingly used for the treatment of various cancers with novel radionuclides, compounds, tracer molecules, and administration techniques. The goal of radiation therapy, including therapy with radiopharmaceuticals, is to optimise the relationship between tumour control probability and potential complications in normal organs and tissues. Essential to this optimisation is the ability to quantify the radiation doses delivered to both tumours and normal tissues. This publication provides an overview of therapeutic procedures and a framework for calculating radiation doses for various treatment approaches. In radiopharmaceutical therapy, the absorbed dose to an organ or tissue is governed by radiopharmaceutical uptake, retention in and clearance from the various organs and tissues of the body, together with radionuclide physical half-life. Biokinetic parameters are determined by direct measurements made using techniques that vary in complexity. For treatment planning, absorbed dose calculations are usually performed prior to therapy using a trace-labelled diagnostic administration, or retrospective dosimetry may be performed on the basis of the activity already administered following each therapeutic administration. Uncertainty analyses provide additional information about sources of bias and random variation and their magnitudes; these analyses show the reliability and quality of absorbed dose calculations. Effective dose can provide an approximate measure of lifetime risk of detriment attributable to the stochastic effects of radiation exposure, principally cancer, but effective dose does not predict future cancer incidence for an individual and does not apply to short-term deterministic effects associated with radiopharmaceutical therapy. Accident prevention in radiation therapy should be an integral part of the design of facilities, equipment, and administration procedures. Minimisation of staff exposures includes consideration of equipment design, proper shielding and handling of sources, and personal protective equipment and tools, as well as education and training to promote awareness and engagement in radiological protection. The decision to hold or release a patient after radiopharmaceutical therapy should account for potential radiation dose to members of the public and carers that may result from residual radioactivity in the patient. In these situations, specific radiological protection guidance should be provided to patients and carers.

Dosimetry perspectives in radiation synovectomy

Rheumatoid arthritis (RA) is a chronic inflammatory disease that can potentially damage the synovial joints. One of the effective treatment modality for RA is radiation synovectomy (RSV) where properly selected radionuclide is injected into the joint space, enabling controlled destruction of diseased synovial membrane via radiation exposure. Radiation dosimetry in RSV appears challenging due to the heterogeneous nature of synovial membrane, nonuniform distribution and leakage of radionuclide from the synovial cavity. This article reviews the dosimetric perspective pertaining to RSV. Specifically, characteristics of radionuclide for RSV and radiation dose to target and non-target (i.e., articular cartilage, bone, bloodstream, gonads, etc.) tissues of patient have been discussed. The personal dose H_p(0.07) to the hands of medical staff (i.e., radiochemist, therapist physician, nurse) may be considerably high due to handling of high specific activities (∼500 MBq/ml for Y-90); such doses are typically measured using thermoluminescence dosimeters (TLD) ring dosimeters and ranges from 1 to 21.5, 0.1 to 40 and 0.1 to 5 µSv/MBq for the radiochemist, therapist physician and the nurse, respectively. Methods to minimize radiation doses to the patient, medical staff and public are elaborated. Contamination risks and precautionary measures are also reported.

Measurement of 131I activity in thyroid of nuclear medical staff and internal dose assessment in a Polish nuclear medical hospital

This paper presents results of 131I thyroid activity measurements in 30 members of the nuclear medicine personnel of the Department of Endocrinology and Nuclear Medicine Holy Cross Cancer Centre in Kielce, Poland. A whole-body spectrometer equipped with two semiconductor gamma radiation detectors served as the basic research instrument. In ten out of 30 examined staff members, the determined 131I activity was found to be above the detection limit (DL = 5 Bq of 131I in the thyroid). The measured activities ranged from (5 ± 2) Bq to (217 ± 56) Bq. The highest activities in thyroids were detected for technical and cleaning personnel, whereas the lowest values were recorded for medical doctors. Having measured the activities, an attempt has been made to estimate the corresponding annual effective doses, which were found to range from 0.02 to 0.8 mSv. The highest annual equivalent doses have been found for thyroid, ranging from 0.4 to 15.4 mSv, detected for a cleaner and a technician, respectively. The maximum estimated effective dose corresponds to 32% of the annual background dose in Poland, and to circa 4% of the annual limit for the effective dose due to occupational exposure of 20 mSv per year, which is in compliance with the value recommended by the International Commission on Radiological Protection.

Occupational radiation exposure of medical staff performing ⁹⁰Y-loaded microsphere radioembolization

PURPOSE

Radioembolization of liver cancer with (90)Y-loaded microspheres is increasingly used but data regarding hospital staff exposure are scarce. We evaluated the radiation exposure of medical staff while preparing and injecting (90)Y-loaded glass and resin microspheres especially in view of the increasing use of these products.

METHODS

Exposure of the chest and finger of the radiopharmacist, nuclear medicine physician and interventional radiologist during preparation and injection of 78 glass microsphere preparations and 16 resin microsphere preparations was monitored. Electronic dosimeters were used to measure chest exposure and ring dosimeters were used to measure finger exposure.

RESULTS

Chest exposure was very low for both products used (<10 μSv from preparation and injection). In our experience, finger exposure was significantly lower than the annual limit of 500 mSv for both products. With glass microspheres, the mean finger exposure was 13.7 ± 5.2 μSv/GBq for the radiopharmacist, and initially 17.9 ± 5.4 μSv/GBq for the nuclear medicine physician reducing to 13.97 ± 7.9 μSv/GBq with increasing experience. With resin microspheres, finger exposure was more significant: mean finger exposure for the radiopharmacist was 295.1 ± 271.9 μSv/GBq but with a reduction with increasing experience to 97.5 ± 35.2 μSv/GBq for the six most recent dose preparations. For administration of resin microspheres, the greatest mean finger exposure for the nuclear medicine physician (the most exposed operator) was 235.5 ± 156 μSv/GBq.

CONCLUSION

Medical staff performing (90)Y-loaded microsphere radioembolization procedures are exposed to safe levels of radiation. Exposure is lower than that from treatments using (131)I-lipiodol. The lowest finger exposure is from glass microspheres. With resin microspheres finger exposure is acceptable but could be optimized in accordance with the ALARA principle, and especially in view of the increasing use of radioembolization.

Exposure of personnel and public due to using 153Sm-labelled EDTMP-Quadramet® in nuclear medicine procedures

The main aim of this study was to highlight the problems of personnel exposure when administering (153)Sm-labelled ethylene diamine tetramethylene phosphonate-Quadramet(®) to patients and especially to evaluate hand exposure of the personnel. The exposure levels of patients' families and the people who takes care of the patients treated by Quadramet(®) were also estimated. Thermoluminescent detectors were used to measure the doses. The doses received during the injection of the Quadramet(®) by the nursing staff have been determined at the level of 1/150 dose limit for the skin. Exposure of members of the patient's family staying 1.5 m away from the patient being treated with Quadramet(®) has been estimated to be 0.40 mGy.

Radiosynovectomy in the therapeutic management of arthritis

Radiosynovectomy is a well-established therapy in arthritis and involves an intra-articular injection of small radioactive particles to treat a synovitis. In Europe, frequent indications are rheumatoid and poly-arthritis. Especially in Germany radiosynovectomy is the second common therapy in Nuclear Medicine with about 40,000–60,000 treated joints per year. In Spain, USA, Turkey, Argentines and Philippines the therapy is more use in hemophilic arthritis with excellent results. Especially in developing countries with low availability of clotting factors, the radiosynovectomy represent a cost effective therapeutic option for repeated bleedings in hemophilic arthropathy. The special focus in these countries is maintaining of mobility and work ability. Often only the knee and medium joints (ankle, elbow and shoulder) are treated using yttrium-90, rhenium-186 or phosphorus-32. However, in rheumatoid arthritis most common affected joints are the fingers. For the treatment in these small joints, erbium-169 is necessary. Unfortunately, erbium-169 is only available in Europe. Further indications for radiosynovectomy are osteoarthritis and the articular effusion after joint replacement. The reported response rates in rheumatoid and poly-arthritis range from 60% to 80% depends from the stage of previous arthrosis. The best effectiveness of therapy was observed in hemophilic arthritis with response rate of 90% and significant reducing of bleeding frequency. The therapy is well-tolerated with low rate of side effects. In respect of the specific uptake of particles in the synovia and short range of beta radiation, the radiation exposure outside the joint is very low. The radiosynovectomy has efforts in comparison to surgical synovectomy: it's a minor intervention with low costs; and simultaneous treatments of multiple joints or treatment in short intervals are possible. The presented paper summarized the published papers and reports our own experiences in >15,000 treated joints.

β-Radiation exposure to fingertips after using a trained routine application method during radiosynovectomy

There are few, but worrisome, data available on fingertip radiation exposure of medical personnel during radiosynovectomy (RSV). To reduce radiation exposure, we performed a dedicated application procedure. This report summarizes the acquired skin equivalent dose [Hp(0.07)] of the personnel involved in the preparation and administration of the three RSV β-emitters Y, Re and Er. Over a period of 3 years, 547 joints in 368 patients were treated with 52421 MBq of the aforementioned three radionuclides. The Hp(0.07) was recorded with thermoluminescence dosimeters worn on the dominant index fingertip and was analysed monthly. Eight staff members were exposed to an Hp(0.07) of 492 mSv. The cumulative dose was less than 10 μSv/MBq. The dose per person was 1.1 μSv/MBq in physicians and up to 4.5 μSv/MBq in technicians. The accumulated personal Hp(0.07) during RSV was far below the regulatory limit and published data.

External radiation exposure of personnel in nuclear medicine from 18F, 99mTC and 131I with special reference to fingers, eyes and thyroid

The radiation exposure of fingers, thyroid and eyes of workers handling radiopharmaceuticals during various nuclear medicine procedures was measured using thermoluminescent dosemeters. Dosemeters were placed on the finger tips of 19 workers on several different occasions for various procedures. Additionally, the routinely determined whole-body doses to various groups of workers were analysed. The finger dose measurements demonstrated clear differences between the various tasks, from 0.0012 µGy MBq(-1) (unpacking and installing (99)Mo/(99m)Tc-generator) to 3.0 µGy MBq(-1) (syringe withdrawal, injection and waste handling of (18)F-FDG). As long as the worker was handling (99m)Tc, the dose to the fingers was well below the ICRP dose limits, even when the activity was high. Special concern should, however, be devoted to the handling of (18)F, since the dose to the fingers could easily reach the dose limits. The estimated dose to eyes and thyroid was well below the dose limits. Since the introduction of the positron emission tomography/computed tomography facility, the annual whole-body dose has increased for those directly involved in the handling of (18)F. The annual whole-body dose of 0.2-2.5 mGy was, however, well below the dose limits.

Reduction of β-radiation exposure during preparation of 188Re-labelled Lipiodol for hepatocellular carcinoma treatment

Rhenium-188 (188Re) is of widespread interest for treating various diseases because of its attractive physical and chemical properties. The routine preparation of therapeutic doses of 188Re-labelled tracers can result in significant radiation exposure to the operator. We studied the impact of automating the preparation of 188Re-Lipiodol on the radiochemist's exposure, as well as the importance of the model of syringe shielding. To monitor radiation exposure continuously readable electronic personal dosimeters were used. Thermoluminescence dosimeters were fixed to the probable most exposed fingers of the radiochemist during preparation of the radiotracer and during the syringing. Dose rates were measured using a Babyline. Automation of the synthesis reduced personal dose equivalents from 2.60±4.35 to 1.61±1.20 µSv/GBq [Hp(10)] and from 38.37±55.28 to 21.84±16.14 µSv/GBq [Hp(0.07)]. Dose to the extremities was also reduced (-80% for the right hand; -58% for the left one). The Lemer-Pax PSWG syringe shield led to a slightly lower dose to the hands compared with the Medisystem (1.1±0.27 vs. 1.34±0.6 mSv/GBq for the right finger). Automation of the synthesis leads to a significant decrease in radiation exposure to the operator. The Lemer-Pax PSWG syringe shield provides better hand protection than the smaller Medisystem Mediclic.

Comparison of two different types of LiF:Mg,Cu,P thermoluminescent dosimeters for detection of beta rays (beta-TLDs) from 90Sr/90Y, 85Kr and 147Pm sources

Targeted radionuclide therapies in nuclear medicine departments increasingly depend on using unsealed beta radiation sources in the labeling of peptides and antibodies. Monitoring doses received by the fingers and hands during these procedures is best accomplished with TLD dosimeters that can be located at the fingertips. The present study examines the response of two TLD dosimeters (MCP-Ns and GR200A) to 90Sr/90Y, 85Kr, and 147Pm. The dosimeters were supplied by two different services, and all irradiations were performed at the PTB Institute in Germany. Each dosimetry service evaluated the dosimeters without knowledge that they had been purposefully irradiated. The accuracy and precision of the dosimeters were evaluated as a function of delivered dose, energy of beta particles and angular incidence. The results are compared to performance measures recommended by the IEC. Both dosimeter types displayed significant energy dependence. Angular dependence was moderate. Accuracy and precision as a function of dose (linearity) differed between the two systems, with the MCP-Ns being noticeably better than the GR200A. The superior precision makes the MCP-Ns much more useful for extremity dose measurements. The differences between these two dosimeter systems reinforce the need to evaluate a dosimeter carefully before using it in the daily work routine.

Radiation protection in 90Y-labelled DOTA-D-Phe1-Tyr3-octreotide preparations

OBJECTIVE

Beta-emitting radionuclides are being increasingly used in targeted radionuclide therapy in nuclear medicine. In particular, the pure high-energy beta-emitter 90Y (Emax=2.27 MeV) has a physical half-life compatible with the pharmacokinetics of peptides. The use of this isotope implies an increase in the radiation dose received by the nuclear medicine staff. The aim of this study is thus the evaluation of the personal beta-dosimetry data related to therapeutic 90Y-labelled DOTA-D-Phe1-Tyr3-octreotide preparation and administration in a nuclear medicine department.

METHODS

Personal dose measurements were carried out with a series of thin active layer ultrasensitive MCP-Ns (LiF: Mg, Cu, P) dosimeters fixed at the operator's fingertips and by means of some direct reading dosimeters; other individual protection devices, such as shielded aprons and anti-X gloves, were also used.

RESULTS

The 95th percentile of the chemist's skin equivalent dose distribution was 1.759 mSv/GBq by using 0.10-mm anti-X gloves and 0.265 mSv/GBq by using 0.20-mm anti-X gloves. The 95th percentile of the physician's skin equivalent dose distribution was 1.198 mSv/GBq by using 0.10-mm anti-X gloves. The use of an anti-X apron during administration permits saving absorbed doses by a factor over 97% for both Hp(10) and Hp(0.07).

CONCLUSION

Because of the physical properties of beta-emitters, an increased number of therapeutic sessions is to be expected. The dose values measured till now, resulting from a high radioprotection level modus operandi, have always respected the threshold limits reported by the European Directive EURATOM 96/29 05/13/1996 for exposed workers, even in addition to other clinical practices in the department.

Radiation dose measurements for personnel performing 90Y-ibritumomab tiuxetan administration: a comparison between two injection methods for dose reduction

The purpose of this study was to directly measure, using thermoluminescent dosimeters, the radiation doses received by radiation team members performing (90)Y-ibritumomab tiuxetan administration. The occupational doses associated with two injection methods for patient administration - an automatic syringe driver and an injection box - were compared. The associated risks, namely cancer induction and hereditary effect, were also estimated from the results and compared with risk factors recommended by the International Commission on Radiological Protection publication 103. The results showed that the doses received by the index and thumb of the right hand and the index finger of the left hand of the radiation oncologist were significantly reduced by using the injection box method. The difference in the dose received by the medical physicist using the two methods was not statistically significant. It was observed that three pairs of latex gloves could further reduce the dose to the hands. The radiological risks of cancer induction and hereditary effect were negligible: of the order of 10(-6) and 10(-7) per (90)Y-ibritumomab tiuxetan administration, respectively, for both methods. However, the results of our study also showed that it would be possible in a busy centre for pregnant women to receive a dose of (90)Y-ibritumomab tiuxetan that exceeds the recommended annual dose limit for the surface of the abdomen.