Purpose: This study aims to assess a dosimetric impact metal artifact reduction in carbon ion radiotherapy with dual-layer dual-energy computed tomography (DL-DECT) in terms of relative stopping power ratio (RSP).
Methods: DL-DECT images of 2 patients implemented metallic structure were analyzed. The scan were performed with a commercial DL-DECT system (IQon Spectral CT, Philips Healthcare). One patient had metal hip implants and the other had a dental implant. Each patient was scanned once and the images were reconstructed with metal artifact reduction (O-MAR) and without metal artifact reduction. When the images were reconstructed, the spectral based images (SBIs) were also acquired to extract effective atomic number (Zeff) and relative electron density (RED) map. By using the Zeff and RED, RSP for each image (i.e., with O-MAR and without O-MAR) were calculated.
Results: Metal artifacts in 120 kVp conventional images were significantly reduced when O-MAR was applied to each image set. In addition, artifacts in Zeff and RED map were also reduced. In both cases of metal hip replacement and dental implant, the difference in RSP ranged from -1.5 to 1.5.
Conclusion: The metal artifacts significantly affected the accuracy of Zeff, RED, RSP, and dose calculation for carbon ion radiotherapy. Adequate metal artifact reduction algorithm is required to be applied in case the patient had metallic implant.
Funding Support, Disclosures, and Conflict of Interest: This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korean government (No. NRF-2019M2A2B4095126 and NRF-2020R1F1A1073430)