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

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 ( GTV s) and organs at risk ( OAR s) 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 GTV prostate 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 GTV P 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 GTV T 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.