¹⁶⁶Ho microsphere scout dose for more accurate radioembolization treatment planning

Excerpt

Radioembolization is nowadays dominated by ^99mTc MAA for pretreatment study of biodistribution and dosimetry, and by ⁹⁰Y microspheres for therapy Physical properties of such radionuclide are: 64 h half-life, beta emission maximal energy 2280 keV, beta abundance 99.9%, no gamma, and 32 positron emissions per million of transformations. A new kind of medical device available for therapy recently became commercially available also for planning: polylactic acid (PLLA) microspheres labeled with ¹⁶⁶Ho. Such radionuclide has a 26.8 h half-life, dual beta emission with maximal energy of 1770 keV (49%)–1850 keV (50%) and, new aspect, it is paramagnetic and it emits gamma photons at 81 keV, with low abundance (6.7%). Gamma photons allow SPECT/CT imaging and dosimetry (some days after therapy to avoid gammacamera saturation) [1], while paramagnetism gives the additional possibility of post-therapy MRI evaluation. Publications about the use of ¹⁶⁶Ho in therapy are available [2, 3], but this application is not under discussion here. …