[P105] A theoretical assesment of patient induced radioactive waste, excreted through the sewers from a department of nuclear medicine

Purpose Planning a new department of Nuclear Medicine (dNM), the radioactivity concentration (rAC) emitted to the environment must be estimated, to ensure the amount released in the public systems remains below the threshold dictated by national regulations [1] . To estimate rAC we propose a theoretical model based on kinetic information from ICRP [2] as these are presumed to be the most accurate available. Methods The model includes known information like: opening hours of the dNM, sewage conditions (flow), patients per year, average dose for an examination, fraction of patients estimated to use the toilets during their stay at the dNM, typical time from injection to toilet visits, and furthermore the bladder activity content at the time of voiding at the dNM, estimated from the kinetic models from the ICRP data. Results We looked at both peak and average rACs. Peak rAC, defined as the concentration from a single flush, was found to be more than the exempt concentration for several examinations (e.g. 0.21 MBq/L HDP, bone scan). With peak rAC as reference, we found that for our new department there will be a need for using storage tanks. This could be the case for most dNM since the examinations exceeding the limits are amongst the most common in the field, however local conditions dictates the need. For an average rAC the exempt limits is easily obeyed at any hospital facility. Conclusions This theoretical way of predicting the release of radioactive waste from a dNM allows us to estimate the rAC emitted to the environment. The model is robust and easily adapted to local conditions. It is based on the best set of kinetic data available and can readily (though cumbersome) be verified experimentally. The work has raised questions - that forces us and our legislators to clarify the level of detail we need to work with when estimating rAC.