Internal dosimetry for yttrium-90 adjuvant therapy against breast cancer

In recent years, the use of compounds labeled with the beta- emitter yttrium-90 is becoming popular in adjuvant therapies following breast cancer resection. The aim of these locoregional approaches is to kill the residual cancer cells in the lesion site (the so-called ”tumor bed”) after surgery. In particular, an interesting technique is the intraoperative avidination of yttrium-90-biotin. This method, fulfilling the definition of pre-targeted radioimmunotherapy (pRIT), is based on the administration of avidin to the tumor bed and subsequent injection of yttrium-90-biotin, which binds avidin and provides irradiation to the region of interest. The main aim of this study, conceived in collaboration with the Medical Physics Unit of the Istituto Romagnolo per lo Studio dei Tumori (IRST) ”Dino Amadori” in Meldola (FC), is to compute the absorbed dose in the tissue with the Monte Carlo method using the Geant software. The absorbed dose will be first computed in generalized geometries, such as spheres or cylinders, and then in virtual voxelized phantoms generated using PET/CT images of patients, in order to obtain 3D dose maps of clinical relevance. Finally, since the imaging quality guaranteed by yttrium-90 is not optimum due to its very low production of gamma rays, another study of interest using the same simulation framework is the comparison of this nuclide with other possible radioactive agents, namely beta emitters with different energy spectra and more intense gamma emissions.