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

Abstract

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 MRI‐images). A common image geometry was defined between the DRR‐ and CkV‐image for each patient. A rigid registration between the GFM center of mass (CoM) coordinates was performed and the distance between each of the GFM in the DRR‐ and registered CkV‐image was calculated. The same methodology was used to assess GFM migration for 31 patients in a CT‐based radiotherapy workflow. The distance calculated was considered a measure of GFM migration. A statistical test was performed to assess any difference between the cohorts. The mean absolute distance difference for the GFM CoM between the DRR‐ and CkV‐image in the MRI‐only cohort was 1.7 ± 1.4 mm. The mean 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 GFM implantation procedure could be used to confirm GFM identification from MRI‐images. GFM migration was present but did not constitute a problem.

MR-PROTECT: Clinical feasibility of a prostate MRI-only radiotherapy treatment workflow and investigation of acceptance criteria

“…After successful implementation of MRI-only, in a clinical routine MRI-only workflow, QA-routines to compensate for the missing CT-information are needed. The GFM-identification process can be verified using for instance X-ray images acquired during GFM-implantation [33]. MRI-only GFM-identification which earlier has been reported a problem in MRI-only [14,17] may thereby be managed using MEGRE.…”

End‐to‐end validation of fiducial tracking accuracy in robotic radiosurgery using MRI‐only simulation imaging

“…Fiducials were inserted using a 15 mm × 15 mm × 15 mm patch around the implanted fiducial centroid. Sites that perform MRI‐only simulation typically voxel burn fiducials in sCT images so this method was included in this study 22 . The fiducial marker contour defined on MRI was voxel burned on sCT to 10000HU.…”

“…Fiducial markers appear as small dark signal voids on MRI and cannot be directly used with robotic radiosurgery fiducial marker tracking software 18–20 . For the clinical use of MRI‐only simulation with standard C‐arm linear accelerator (linac)‐based treatments, fiducials identified on MRI are voxel burned at the same location in their corresponding sCT images 21,22 . In treatments using C‐arm linacs, radiation therapists typically manually identify fiducial locations, which is why a voxel‐burned fiducial suffices 8 .…”

“…[18][19][20] For the clinical use of MRI-only simulation with standard C-arm linear accelerator (linac)based treatments, fiducials identified on MRI are voxel burned at the same location in their corresponding sCT images. 21,22 In treatments using C-arm linacs, radiation therapists typically manually identify fiducial locations, which is why a voxel-burned fiducial suffices. 8 However, in robotic radiosurgery, fiducial detection algorithms are designed to automatically detect fiducial markers in X-ray images using methods such as normalized cross correlation and template matching.…”

Radiation induced therapeutic effects in cancerous and tumor cells: A review

“…85 The diagnostic method is magnetic resonance imaging (MRI) using intraprostatic gold fiducial markers (GFM). 86 Modern radiotherapy techniques of intensity-modulated radiotherapy are used to modify risk. 87 Prostate cancer cells become metastatic, altering the organ microenvironment and their interactions.…”