Evaluation of an automatic MR-based gold fiducial marker localisation method for MR-only prostate radiotherapy

Abstract

An MR-only radiotherapy planning (RTP) workflow would reduce the cost, radiation exposure and uncertainties introduced by CT-MRI registrations. In the case of prostate treatment, one of the remaining challenges currently holding back the implementation of an RTP workflow is the MR-based localisation of intraprostatic gold fiducial markers (FMs), which is crucial for accurate patient positioning. Currently, MR-based FM localisation is clinically performed manually. This is sub-optimal, as manual interaction increases the workload. Attempts to perform automatic FM detection often rely on being able to detect signal voids induced by the FMs in magnitude images. However, signal voids may not always be sufficiently specific, hampering accurate and robust automatic FM localisation. Here, we present an approach that aims at automatic MR-based FM localisation. This method is based on template matching using a library of simulated complex-valued templates, and exploiting the behaviour of the complex MR signal in the vicinity of the FM. Clinical evaluation was performed on seventeen prostate cancer patients undergoing external beam radiotherapy treatment. Automatic MR-based FM localisation was compared to manual MR-based and semi-automatic CT-based localisation (the current gold standard) in terms of detection rate and the spatial accuracy and precision of localisation. The proposed method correctly detected all three FMs in 15/17 patients. The spatial accuracy (mean) and precision (STD) were 0.9 mm and 0.5 mm respectively, which is below the voxel size of [Formula: see text] mm and comparable to MR-based manual localisation. FM localisation failed (3/51 FMs) in the presence of bleeding or calcifications in the direct vicinity of the FM. The method was found to be spatially accurate and precise, which is essential for clinical use. To overcome any missed detection, we envision the use of the proposed method along with verification by an observer. This will result in a semi-automatic workflow facilitating the introduction of an MR-only workflow.

Improving fiducial and prostate capsule visualization for radiotherapy planning usingMRI

“…There have been a number of studies investigating dedicated MRI sequences for fiducial detection . Both balanced steady‐state free precession sequences and sequences based on spoiled gradient‐echoes have been employed in 2D and 3D acquisitions, relying on T2*‐related signal loss to create a detectable signal void in the vicinity of the fiducials. The averaging of consecutive echoes in multi‐echo recalled sequences, such as the one used here is an attractive mechanism to increase the signal‐to‐noise ratio.…”

“…The accuracy of fiducial detection is paramount and can be either manual or automatic . However, ultimately, this must be performed automatically, especially if intrafractional imaging is to be used.…”

“…However, ultimately, this must be performed automatically, especially if intrafractional imaging is to be used. Different methods have been described for automatic algorithms including feature extraction and template matching . The fiducial detection is dependent on the signal loss, which varies with factors including seed orientation and TE .…”

“…Studies so far for similar sequences have focused on accuracy of fiducial detection . In this article we examine the T2*W sequence and investigate whether it is possible to use this sequence alone in prostate studies, considering geometric integrity, the ability to locate marker positions and the ability to provide enough contrast for prostate volume outlining.…”

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

“…In T2‐weighted (T2w) MRI‐images, GFM, calcifications and bleeding will have similar signal behavior and be depicted as signal voids . This makes differentiating between these objects a challenging task using solely MRI‐images in an MRI‐only radiotherapy workflow.…”