Feasibility of the analytical dose calculation method for Au-198 brachytherapy

A dose calculation algorithm Computed Tomography (CT)-based analytical dose calculation method (CT_anly), which can correct for subject inhomogeneity and size-dependent scatter doses, was applied to the ¹⁹⁸Au seed. In this study, we evaluated the effectiveness of the CT_anly method by comparing the gold standard Monte Carlo (MC) method and the conventional TG43 method on two virtual phantoms and patient CT images simulating oral cancer.

As virtual phantoms, a water phantom and a heterogeneous phantom with soft tissue inserted cubic fat, lung, and bone were used. A 2-mm-thick lead plate was also inserted into the heterogeneous phantom as a dose attenuator. Virtual ¹⁹⁸Au seeds and a 2-mm-thick lead plate were placed on the patient CT images. Dose distributions obtained via the TG43 and CT_anly methods were compared with those of the MC by gamma analysis with 2%/2-mm thresholds. The computation durations were also compared.

In the water phantom, dose distributions comparable to those obtained via the MC method were obtained regardless of the algorithm. For the inhomogeneity phantom and patient case, the CT_anly method showed an improvement in the gamma passing rate and dose distributions similar to those of the MC method were obtained. The computation time, which was days with the MC method, was reduced to minutes with the CT_anly method.

The CT_anly method is effective for ¹⁹⁸Au seed dose calculations and takes a shorter time to obtain the dose distributions than the MC method.