Synthesis, characterization and dosimetry of Ho and HoZr radioactive seeds for breast cancer treatment

This study addresses the synthesis, characterization and dosimetry of radioactive bioglass seeds of Ho and HoZr aiming to produce a booster of absorbed dose by breast brachytherapy with Ho-166 seeds, complementary to the teletherapy or applied in a unique way. The methodology consisted in the synthesis and chemical, nuclear and metallurgical characterizations of the bioglass seeds with holmium and holmium-zirconium. A compressed breast phantom has been enhanced to dosimetric evaluations, as well as the construction of a breast phantom in natural position. The experimental dosimetry of brachytherapy with implants of radioactive bioglass Ho-166 seeds was performed with radiochromic films, and compared with theoretical dosimetry by code MCNP-5. The experimental dosimetry in radiotherapy planning for natural breast phantom was also performed, and compared with computational dosimetry from radiotherapy planning. As a result the bioglass Ho and HoZr seeds of 0.6 mm diameter and 1.6 mm length were obtained and encapsulated in polymer and resin. The UV-VIS spectrophotometry showed the presence of Ho-165 at a concentration of 30.7% in HoZr. K or L-edge X-ray emissions of Zr and gamma rays of Ho-166 were quantified. The scanning electron microscopy identified the surface topology of the bioglass seeds and their grain size. The characteristic peaks of Si, Ca, Ho were identified by X-ray fluorescence by EDS, where the weight concentrations of C, O, Si, Ca, were obtained. Ho and Zr were also identified by X-ray fluorescence with Am-241 excited source. The evaluation of the Zr mass attenuation coefficient showed to be 10 times higher than Ho. After evaluation of radioactive contaminants, the activity of Zr-97 was negligible compared with natural activity of the human body. The phantoms reproduced an equivalent radiological response to the human breast. The measured doses in brachytherapy from beta emissions of HoZr bioglass seed showed equivalence into the range of 2.7 to 10 mm to data generated by MCNP-5. The same occurred for gamma emissions in the range of 11 to 21 mm. The breast phantom dosimetry showed the spatial distribution of doses, being equivalent to the radiotherapy planning, in which 2.28 Gy was applied. The results suggest that implants of the Ho and HoZr radioactive bioglass seeds in breast may be an alternative to radiotherapy, producing a spatial distribution of absorbed dose in tissue, additional to the teletherapy. (author)