Clinical relevance of metal artefact reduction in computed tomography (iMAR) in the pelvic and head and neck region: Multi‐institutional contouring study of gross tumour volumes and organs at risk on clinical cases

INTRODUCTION: Artefacts caused by dental implants and hip replacements may impede target volume definition and dose calculation accuracy. The iterative metal artefact reduction (iMAR) algorithm can provide a solution for this problem. The present study compares delineation of gross tumour volumes (GTVs) and organs at risk (OARs) in the pelvic and the head and neck (H & N) regions using computed tomography (CT) with and without iMAR, and thus the practical applicability of iMAR for routine clinical use. METHODS: The native planning CT and CT-iMAR data of two typical clinical cases with image-distorting artefacts were used for multi-institutional contouring and analysis using the Dice similarity coefficient (DSC). GTV/OAR contours were compared with an intraobserver approach and compared to predefined reference structures. RESULTS: Mean volume for GTVprostate in the intraobserver approach decreased from 87 +/- 44 cm(3) (native CT) to 75 +/- 22 cm(3) (CT-iMAR) (P = 0.168). Compared to the reference, DSC values for GTVP rostate increased from 0.68 +/- 0.15 to 0.78 +/- 0.07 (CT vs. iMAR) (P < 0.05). In the H & N region, the reference for GTVT ongue (34 cm(3) ) was underestimated on both data sets. No significant improvement in DSC values (0.83 +/- 0.06 (native CT) versus 0.86 +/- 0.06 (CT-iMAR)) was observed. CONCLUSION: The use of iMAR improves the anatomical delineation at the transition of prostate and bladder in cases of bilateral hip replacement. In the H & N region, anatomical residual structures and experience were apparently sufficient for precise contouring.