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A CT-Based Monte Carlo Dose Calculation for Correction of Metal Artifacts Due to the Henschke Applicator


P Yu

P Yu1,2*, T Chao3, C Lee3, C Tung3, C Wu2, H Lee4, H Nien2, P Tu4, (1)National Tsing-Hua Univ, Hsinchu, ,(2) Cathay General Hospital, Taipei, Taiwan, ,(3) Chang Gung University, Tao-Yuan, ,(4) Sijhih Cathay General Hospital, New Taipei City, Taiwan

SU-E-T-323 Sunday 3:00:00 PM - 6:00:00 PM Room: Exhibit Hall

Purpose:
Monte Carlo method is the most accurate dose calculation system in the modern world. And we use it to evaluate the influence of computed tomography (CT) metal artifacts resulted from the Henschke applicator in intracavitary brachytherapy dose distribution.

Methods:
The CT images of the Plastic Water® phantom with Henschke applicator and the applicator associated metal artifacts are applied to the Monte Carlo N-Particle Transport Code X (MCNPX) for dose calculation. The accuracy of the CT images input is assessed by the phantom dose simulation with and without CT images based on our previous Monte Carlo parameters optimization. To reduce the effect of artifacts, the HU number of metal artifacts and metal materials in CT images are replaced by phantom HU number according to the redefined HU density table. Then the Henschke applicator geometry is superimposed on the corrected CT image. This corrected CT images are applied to MCNPX for dose calculation. The dose calculation with and without metal artifacts can be analyzed for the impact of metal artifacts.

Results:
This system can be implemented because the dose discrepancy with and without CT images is below 0.05%. We analyze the dose distribution with corrected CT-based phantom for the impact of metal artifacts. The dose distribution shows the largest dose discrepancy is 8-9% and which is located at the region above 2cm distal to ovoid edge.

Conclusions:
In this study, the dose at the region above 2cm distal to ovoid edge is significantly under prescription dose. The artifacts resulted from Henschke applicator leads to a certainly inaccurate dose calculation in the planning system. Thus, dose distribution must be evaluated before using new applicator. The CT-based Monte Carlo method can be used to evaluate the influence of CT metal artifacts in intracavity brachytherapy.

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