Transport of Tb radioisotopes - Determination of A1 and A2 values

Nuclear medicine is a scientific branch that makes use of radioactive nuclei to diagnose and treat certain diseases. A very interesting chemical element for this purpose is terbium. This element has four different isotopes that can be applied in nuclear medicine. $^{149}$Tb and $^{161}$Tb can be used in the treatment of diseases using $\alpha$-therapy and $\beta^-$- and Auger therapy, respectively. $^{152}$Tb and $^{155}$Tb have applications in the Positron Emission Tomography (PET) and Singe Photon Emission Computed Tomography (SPECT) imaging techniques, respectively. Since the four isotopes are chemically similar, they can all bind to the same molecule that is used as a tracer. This makes terbium extremely useful in the branch of nuclear medicine that combines therapy and diagnostics: theranostics. For the transport of radiopharmaceuticals, so-called A1 and A2 values are determined for each radioisotope. These are the activity limits for the isotope to be transported in a type A package as a sealed source or open source, respectively. If the limits are exceeded, the isotope must be transported in a larger and more expensive type B package. The A1 and A2 values of $^{152}$Tb and $^{155}$Tb have not been determined yet, so that these isotopes are subject to very conservative limits. Right now, the expected activity at which $^{152}$Tb is expected to be produced in the future, exceeds its A2 value. To this end, the Belgian and the international regulation on transport of radioisotopes are investigated. The International Atomic Energy Agency (IAEA) provides regulations on the determination of A1 and A2 values using the so-called Q system. This system is used to calculate the activity limits for all four Tb isotopes. For every isotope five Q values, labeled QA through QE, have to be determined. IAEA defines each Q value and gives the appropriate formulas that need to be used for their calculation. However, it is not specified which source material or interpolation methods for tabulated values needs to be used. A comparison of the values calculated in this work with values calculated by a third-party software, shows that there are indeed some numerical differences between the two calculation methods. After the rounding of the values, the calculated A1 and A2 values do agree, except for $^{155}$Tb, where they differ slightly. To overcome this inconvenience, another methodology to calculate Q values is investigated in the last part of this work. Instead of using tabulated values from old experiments, Monte Carlo simulations are performed using the FLUKA software package. There seems to be some discrepancy between the values calculated the numerical way and the values calculated with FLUKA. However, when comparing the Monte Carlo results from this work with literature values that were also obtained using a Monte Carlo method, it seems that this method leads to more consistent results.