Potential airborne releases of theranostic radionuclides 68Ga and 177Lu: a method of preventive assessment of the radiological impact

Introduction: The handling of radioactive solutions can lead to the production of airborne radioactivity which can potentially be released into the environment. To reduce this risk to a minimum, containment and protection systems are adopted. However, during processing, unwanted situations may occur, releasing some radioactivity. Given the high activity concentration levels of the products, even a small volume can contain significant radionuclide activity. In this work we present a method for preventive risk assessment, evaluating the potential release of radioactive gases in the case of two important theranostic radionuclides, 68Ga and 177Lu. Materials & Methods: The source term, the amount of radioactivity released to air, can be evaluated according to the method introduced by the US Department of Energy. For a liquid to be made airborne, in realistic situations, the bulk liquid must be subdivided into droplets small enough to be entrained in the local airflow. Not considering explosions or fires, this may have different causes, like heating the solution, fall and rupture of the container or resuspension due to the aerodynamic action of ventilation. The key point is the evaluation of the airborne release factor (ARF), the fraction of activity that is released to the air. For all the following calculations, we assumed a single, conservative ARF value of 3 × 10–5, according to DOE Handbook 3010 for heating of aqueous solutions. To assess the effective dose to the population living in the area surrounding the facility, two scenarios of clinical activity with a total use of 4.5 GBq/day of 68Ga and of 20 GBq of 177Lu twice per week were developed. The well-known code HotSpot was used to calculate the total effective dose, including resuspension effects, to the reference person of the population. In order to consider the worst-case scenario, the absence of filters was assumed. Results: The total annual releases in the worst case resulted of 29.9 MBq for 68Ga and of 60 MBq for 177 Lu. The maximum effective dose values calculated for the close proximity of the facility were 0.01 µSv/year for 177Lu and 0.0031 µSv/year for 68Ga. Conclusions: The requirements in radiation protection regulations regarding the control of the impact of Nuclear Medicine facilities on the environmental and population have become more stringent over the years. Requests to prepare preventive environmental impact assessments of effluents are increasing. In this work, we have presented a simple calculation method, using international reference documents and calculation codes, which are based on a solid scientific basis. The estimates we have presented using the two relevant theranostic radionuclides 68Ga and 177Lu as an example, show that the impact of the potential releases of an ‘average' center does not cause a radiologically relevant hazard, even in the very conservative assumed conditions.