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.
Highlights
The use of magnetic resonance imaging (MRI) for target delineation in prostate cancer radiotherapy is widespread due to the superior soft tissue contrast of MRI compared to computed tomography (CT)
In a conventional radiotherapy workflow for prostate, CT, and MRI are used in combination by registering the images into a common frame of reference
We suggest that the gold fiducial markers (GFM) position information from the X‐ray images could be used to differentiate GFM from other objects in the MRI‐images
Summary
The use of magnetic resonance imaging (MRI) for target delineation in prostate cancer radiotherapy is widespread due to the superior soft tissue contrast of MRI compared to computed tomography (CT). Prostate external beam radiotherapy workflows where CT is excluded and solely based on MRI, referred to as an MRI‐only radiotherapy workflow, have been introduced into the clinic.[1,2]. Systematic uncertainties such as image registration errors between CT and MRI could thereby be eliminated.[3,4]. Two commercial solutions for prostate sCT generation exist, Philips MRCAT and Spectronic MriPlanner.[5,6]. Both solutions have been independently validated and have been or are being used in clinical studies.[1,7,8]. Two commercial solutions for prostate sCT generation exist, Philips MRCAT and Spectronic MriPlanner.[5,6] Both solutions have been independently validated and have been or are being used in clinical studies.[1,7,8] Multiple other solutions for generating a sCT have been presented and were recently reviewed.[9]
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