Effective and equivalent dose minimization for personnel in PET procedures: how far are we from the goal?

Development of the occupational exposure during the production and application of radiopharmaceuticals in Germany

An increasing number of radiopharmaceuticals and proteins are available for diagnosing and treating various diseases. The demand for existing and newly developed pharmaceutical radionuclides and proteins is steadily increasing. The radiation exposure levels of workers in the radiopharmaceutical industry and nuclear medicine field are closely monitored, specifically their effective dose and equivalent dose, leading to the question, of whether the dawn of radiopharmaceuticals affects the occupational exposure level. This development is analyzed and evaluated with data from the German National Dose Register. Data shows that the effective dose in the work categories production and distribution of radioisotopes as well as nuclear medicine slightly decreased from 1997 to 2021. Over the same period, the hand equivalent dose in nuclear medicine increases steadily, with no discernible trend in production and distribution of radioisotopes. Over the past few decades, intentional efforts and measures have been taken to ensure radiation protection. Instruments for monitoring and dose reduction must be continuously applied. Given the low effective dose, the focus in future shall be on dose reduction following theaslowasreasonablyachievable principle. The development of the hand equivalent dose should be carefully observed in the upcoming years.

The relative contribution of photons and positrons to skin dose in the handling of PET radiopharmaceuticals

BACKGROUND

Despite recommendations to use syringe and vial shields to reduce exposure of the hands of staff when manipulating PET radiopharmaceuticals, operators sometimes prefer to work without shields, believing that the faster handling limits the equivalent dose. The aim of this work is to show that this approach does not properly consider the contribution of positrons to the dose.

MATERIALS AND METHODS

Using the Varskin+ code, skin doses were calculated for syringes of various sizes, filled with ¹⁸F, ¹¹C or ⁶⁸Ga solution. Syringes without shielding, or shielded with 2 mm and 10 mm of tungsten were considered.

RESULTS

Dose rate values in mSv/s per MBq, averaged on a 1 cm² surface at a depth of 0.07 mm were calculated for all the above conditions. For example, in the case of 3 mL ¹⁸F syringe at 1 mm from the skin, the dose rate without shielding is 1.32E-02 and 8.63E-04 for positrons and photons respectively. For ¹¹C, the corresponding dose rates are 4.70E-02 and 8.90E-04 respectively, and for ⁶⁸Ga, 8.52E-02 and 9.48E-04.

CONCLUSIONS

Our results show that the dose due to positrons is the principal component of skin irradiation, by a factor of 3-100, depending on the conditions. The use of shields for syringes and vials is necessary to avoid unjustified skin exposures, that may challenge dose limits. In our opinion, automatic systems for dispensing and allowing injection with shielded syringes, or automatic injectors, are economically justified and should be adopted in PET.

A simple, reliable and accurate approach for assessing [131I]-capsule activity leading to significant reduction of radiation exposure of medical staff during radioiodine therapy

PURPOSE

According to German law, the [¹³¹I]-capsule activity has to be checked in the context of radioiodine therapy (RIT) immediately before application. The measurement leads to significant radiation exposure of the medical personnel, especially of their hands. We aimed to establish a method for estimating [¹³¹I]-capsule activity by measuring the dose rate (DR) at contact of the delivered lead closed container carrying the [¹³¹I]-capsules and to evaluate radiation exposure in comparison to conventional [¹³¹I]-capsule measurement using a dose calibrator.

METHODS

DR on the surface of the closed lead container was measured at two locations and correlated linearly with the [¹³¹I]-capsule activity measured in a dose calibrator to create calibrating curves. The hand and whole body (effective) doses were determined with official dose meters during validation of our method in clinical practice.

RESULTS

The determination coefficients (R²) of linear calibration curves were greater than 0.9974. The total relative uncertainty for estimating [¹³¹I]-capsule activity with our method was <±7.5% which is lower than the uncertainty of the nominal activity and quite close to the threshold limit for the maximum allowed uncertainty of ± 5% for measuring activity in radioactive drugs. The reduction of the hand dose caused by our method was 97% compared with the conventional measurements of the [¹³¹I]-capsules in a dose calibrator.

CONCLUSION

Measuring DR on the surface of the closed lead containers enables the [¹³¹I]-capsules activity to be estimated simply, reliably and with sufficient accuracy leading to significant reduction of the radiation exposure for the medical staff.

Using Monte Carlo methods for Hp(0.07) values assessment during the handling of 18F-FDG

The dose limit for the skin of the hand is typically converted to a surface of 1 cm², which means that one needs to measure point doses in different places on the hand. However, the commonly used method of measuring doses on the hand, i.e., using a dosimetric ring including one or several thermoluminescent detectors worn at the base of a finger, is not adequate for manual procedures such as labeling or radiopharmaceutical injection. Consequently, the purpose of this study was to create and conduct a series of computer simulations that, by recreating the actual working conditions, would provide information on the values of ionizing radiation doses received by the most exposed parts of the hands of employees of radiopharmaceutical production facilities, as well as those of nurses during the injection of radiopharmaceuticals. The simulations were carried out using Monte Carlo radiation transport calculations. The H_p(0.07) personal dose equivalent values obtained for the fingertips of the index and middle fingers of nursing staff and chemists were within the range limited by the minimum and maximum H_p(0.07) values obtained as a result of dosimetric measurements carried out in diagnostic and production centers. Only in the case of the nurse's fingertip, the simulated value of H_p(0.07 slightly exceeded the measured maximum H_p(0.07) value. The comparison of measured and simulated dose values showed that the largest differences in H_p(0.07) values occurred at the thumb tip, and for ring finger and middle finger of some of the nurses investigated.

Use of a radiopharmaceutical multidose dispenser for positron emission tomography: Risk assessment and mitigation measures for infection prevention

Positron emission tomography (PET) imaging necessitates the use of multidose vials for radiopharmaceutical delivery to patients. Conventional practices involve manual extraction of radiopharmaceuticals from a multidose vial prior to each PET procedure, which exposes the technologist to increasing levels of radiation and poses a potential infection risk to patients with frequent handling and access of the vial. New technologies for automated dosing and infusion delivery are available, however these incorporate both a multidose vial and a multi-patient infusion set. There is an absence of guidance for infection prevention (IP) units regarding the safety and acceptability of these devices. This paper describes the process of risk assessment and the mitigation measures for training, workflows, and documentation which led to the safe introduction of an automated PET infusion device in a large tertiary public healthcare facility.