Using C‐Arm X‐ray images from marker insertion to confirm the gold fiducial marker identification in an MRI‐only prostate radiotherapy workflow

摘要

Prostate cancer radiotherapy workflows, solely based on magnetic resonance imaging (MRI), are now in clinical use. In these workflows, intraprostatic gold fiducial markers (GFM) show similar signal behavior as calcifications and bleeding in T2‐weighted MRI‐images. Accurate GFM identification in MRI‐only radiotherapy workflows is therefore a major challenge. C‐arm X‐ray images (CkV‐images), acquired at GFM implantation, could provide GFM position information and be used to confirm correct identification in T2‐weighted MRI‐images. This would require negligible GFM migration between implantation and MRI‐imaging. Marker migration was therefore investigated. The aim of this study was to show the feasibility of using CkV‐images to confirm GFM identification in an MRI‐only prostate radiotherapy workflow. An anterior‐posterior digitally reconstructed radiograph (DRR)‐image and a mirrored posterior‐anterior CkV‐image were acquired two weeks apart for 16 patients in an MRI‐only radiotherapy workflow. The DRR‐image originated from synthetic CT‐images (created from style="fixed-case">MRI‐images). A common image geometry was defined between the style="fixed-case">DRR‐ and CkV‐image for each patient. A rigid registration between the style="fixed-case">GFM center of mass (CoM) coordinates was performed and the distance between each of the style="fixed-case">GFM in the style="fixed-case">DRR‐ and registered CkV‐image was calculated. The same methodology was used to assess style="fixed-case">GFM migration for 31 patients in a style="fixed-case">CT‐based radiotherapy workflow. The distance calculated was considered a measure of style="fixed-case">GFM migration. A statistical test was performed to assess any difference between the cohorts. The mean absolute distance difference for the style="fixed-case">GFM CoM between the style="fixed-case">DRR‐ and CkV‐image in the style="fixed-case">MRI‐only cohort was 1.7 ± 1.4 mm. The mean style="fixed-case">GFM migration was 1.2 ± 0.7 mm. No significant difference between the measured total distances of the two cohorts could be detected (P = 0.37). This demonstrated that, a C‐Arm X‐ray image acquired from the style="fixed-case">GFM implantation procedure could be used to confirm style="fixed-case">GFM identification from style="fixed-case">MRI‐images. style="fixed-case">GFM migration was present but did not constitute a problem.