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Parametric Model Adjustment of Prescribed Mean Radiation Dose to Ensure Complete Coverage at Tumor Margins During Ablative 90Y Radioembolization

S Kappadath1*, B Lopez1, A Braat2, R DiTusa1, A Mahvash1, B Toskich3, (1) University of Texas MD Anderson Cancer Center, Houston, TX, USA (2) University Medical Center, Utrecht, NL (3) Mayo Clinic, Jacksonville, FL, USA

Presentations

(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.

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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.

Keywords

Radiation Dosimetry, Nuclear Medicine, Tumor Control

Taxonomy

IM- Nuclear Medicine General: Radiation dosimetry & risk

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