| 總結: | High-dose-rate (HDR) brachytherapy employing Iridium-192 is a recognized
technique for the treatment of tongue cancer, providing the benefit of delivering highly
conformal doses while protecting adjacent critical structures. The American Association of
Physicists in Medicine Task Group 43 (AAPM TG 43) formalism serves as the prevailing
clinical standard for dose calculations; however, it operates under the assumption of a
uniform water environment, thereby overlooking patient-specific anatomical differences.
This study examines the variances between the AAPM TG 43 formalism and Monte Carlo
(MC) simulations utilizing the egs_brachy application, which facilitates more precise patientspecific
dose calculations by incorporating heterogeneities.
CT datasets from three patients with tongue cancer who underwent HDR
brachytherapy were examined. Treatment plans based on AAPM TG-43 were created using
the Oncentra Brachy Treatment Planning System (TPS). Subsequently, these plans were
transferred into the egs_brachy MC simulation framework through the eb_gui interface,
enabling voxel-based modeling of patient anatomy and the simulation of dose distributions
with detailed tissue assignment schemes. Dose Volume Histograms (DVHs) and statistical
metrics such as D90, D100 for the Planning Target Volume (PTV), and D0.1cc, D1.0cc, and D2.0cc
for organs at risk (OARs) were evaluated across both methodologies. The results indicated
significant differences in the dosimetric parameters between the AAPM TG-43 and MC
simulations. The AAPM TG-43 approach typically overestimated doses to the GTV while
underestimating doses to specific OARs, highlighting its limitations in addressing patientspecific
anatomical complexities. These findings emphasize the potential of MC simulations using egs_brachy as a more precise and reliable alternative for dose calculation in HDR
brachytherapy, especially in anatomically intricate regions such as the oral cavity
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