Systematic investigation on the validity of partition model dosimetry for Y-90 radioembolization using Monte Carlo simulation

摘要

We aimed to investigate the validity of the partition model (PM) in estimating the absorbed doses to liver tumour (D-T), normal liver tissue (D-NL) and lungs (D-L), when cross-fire irradiations between these compartments are being considered. MIRD-5 phantom incorporated with various treatment parameters, i. e. tumour involvement (TI), tumour-to-normal liver uptake ratio (T/N) and lung shunting (LS), were simulated using the Geant4 Monte Carlo (MC) toolkit. 10(8) track histories were generated for each combination of the three parameters to obtain the absorbed dose per activity uptake in each compartment (D-T(AT), D-NL(ANL), and D-L(AL)). The administered activities, A were estimated using PM, so as to achieve either limiting doses to normal liver, D-NL(lim) or lungs, D-L(lim) (70 or 30 Gy, respectively). Using these administered activities, the activity uptake in each compartment (A(T), A(NL), and A(L)) was estimated and multiplied with the absorbed dose per activity uptake attained using the MC simulations, to obtain the actual dose received by each compartment. PM overestimated D-L by 11.7% in all cases, due to the escaped particles from the lungs. D-T and D-NL by MC were largely affected by T/N, which were not considered by PM due to cross-fire exclusion at the tumour-normal liver boundary. These have resulted in the overestimation of D-T by up to 8% and underestimation of D-NL by as high as -78%, by PM. When D-NL(lim) was estimated via PM, the MC simulations showed significantly higher D-NL for cases with higher T/N, and LS <= 10%. All D-L and D-T by MC were overestimated by PM, thus D-L(lim) were never exceeded. PM leads to inaccurate dose estimations due to the exclusion of cross-fire irradiation, i.e. between the tumour and normal liver tissue. Caution should be taken for cases with higher TI and T/N, and lower LS, as they contribute to major underestimation of D-NL. For D-L, a different correction factor for dose calculation may be used for improved accuracy.