(Sunday, 7/12/2020) [Eastern Time (GMT-4)]
Room: AAPM ePoster Library
Purpose: Beta particles from 90Y decay (Emax=2.23MeV) have mean range of 2-4 mm in tissue. Therefore, tumor margins and hypo-perfused cores may not receive the prescribed ablative doses in segmental 90Y-radioembolization where complete pathological response is desired. We present a parametric model for adjustments of prescribed dose to mitigate radiation dose losses at tumor margins and cores.
Methods: Spherical tumors (diameters 10
Results: The multi-parametric models were: Dmean(Dt,Fb) = 1-(4.6/Rt)*(1-Fb); Dmargin(l,Fb) = 1/[1.3*exp(0.8*l)+1]+Fb/[1.3*exp(-0.8*l)+1]; Dcenter(Dc,Fc) = 1.4*exp(-0.15*Dc)+0.4*exp(0.05*Dc)*Fc. Dmean in uniformly-perfused tumors ranged 0.84-0.95 for Dt >2cm but was underestimated as 0.55-0.84 for Dt =2cm. In tumors with Dt >2cm, Dmargin, found to be sigmoidal with l, was 0.76, 0.39, and 0.11 at l=-2mm (inside), 0mm (margin), and +2mm (outside) for all Rt with Fb=0. In hypo-perfused cores with rim thicknesses >1cm, Dcenter increased linearly with Fc and received additional dose contributions from the rim activity (from crossfire effect) when Dc <2cm.
Conclusion: The prescribed mean tumor dose needs to be increased by 250% and by 900% to achieve that same prescribed dose at the tumor margin and +2mm beyond the tumor margin. Hypo-perfused cores with diameters <1cm receive a minimum 20% of the prescribed dose even when there is no uptake in core. Parametric modelling has also been extended to other theranostic radionuclides, Ho-166 and Lu-177.
Funding Support, Disclosures, and Conflict of Interest: SCK serves as consultant for Boston Scientific, Sirtex, ABK Biomedical, Varian Medical. AM serves as consultant for Boston Scientific, Sirtex, ABK Biomedical.
Radiation Dosimetry, Nuclear Medicine, Tumor Control
IM- Nuclear Medicine General: Radiation dosimetry & risk