The impact of image acquisition time on registration, delineation and image quality for magnetic resonance guided radiotherapy of prostate cancer patients

Abstract

Background and Purpose Magnetic resonance (MR) guided radiotherapy utilizes MR images for (online) plan adaptation and image guidance. The aim of this study was to investigate the impact of variation in MR acquisition time and scan resolution on image quality, interobserver variation in contouring and interobserver variation in registration. Materials and Methods Nine patients with prostate cancer were included. Four T2-weighted 3D turbo spin echo (T2w 3D TSE) sequences were acquired with different acquisition times and resolutions. Two radiologists assessed image quality, conspicuity of the capsule, peripheral zone and central gland architecture and motion artefacts on a 5 point scale. Images were delineated by two radiation oncologists and interobserver variation was assessed by the 95% Hausdorff distance. Seven observers registered the MR images on the planning CT. Registrations were compared on systematic offset and interobserver variation. Results Acquisition times ranged between 1.3 and 6.3 min. Overall image quality and capsule definition were significantly worse for the MR sequence with an acquisition time of 1.3 min compared to the other sequences. Median 95% Hausdorff distance showed no significant differences in interobserver variation of contouring. Systematic offset and interobserver variation in registration were small (<1 mm) and of no clinical significance. Conclusions Our results can be used to effectively shorten overall fraction time for online adaptive MR guided radiotherapy by optimising the imaging sequence used for registration. From the sequences studied, a sequence of 3.1 min with anisotropic voxels of 1.2 × 1.2 × 2.4 mm 3 provided the shortest acquisition time without compromising image quality.

Evaluation of non-vendor magnetic resonance imaging sequences for use in bladder cancer magnetic resonance image guided radiotherapy

“…Workflow time for the 1.1min3mm sequence was reduced substantially above the time attributed to reduced image acquisition alone. Further time savings were due to smaller imaging data size and quicker data transfer steps within the workflow, also noted in previous studies [8] . As the 1.1min3mm sequence offered workflow time reduction whilst maintaining sufficient image quality, it was approved for clinical use by senior delegates from all professions within the MDT.…”

“…The qualitative review assessment was designed to reflect the purpose of the images within the bladder MRIgRT workflow. Other studies use similar qualitative reviews tailored to their workflow under investigation, including Likert or scoring scales aligned with our methodology [5] , [8] , [17] , [18] . Our approach was chosen to facilitate efficient assessment and reduce review ambiguity.…”

“…MRI sequences are provided for MR-linac workflows by the vendors; however, these are often designed for use over multiple anatomical areas and may not be fully optimised for the specific target site in question [3] , [4] . Alternative sequences may offer advantages such as improved image contrast, faster acquisition or motion assessment information, and new sequences have already been proposed for use in MR-linac workflows [5] , [6] , [7] , [8] . International derived consensus guidance is available for RT-specific MRI protocol optimisation, and gives recommendations for receiver bandwidth, resolution, and acquisition types [9] , [10] .…”

ICRU REPORT 97: MRI-Guided Radiation Therapy Using MRI-Linear Accelerators

“…As a result, the accuracy of target verification in the breathing direction may be somewhat compromised. Although these solutions are now commercially available, several groups have pursued the generation of 4D MRI sequences to characterize the full respiratory cycle (Nowee et al , 2021; Stemkens et al , 2018). The solutions that are based on a stack of stars acquisition typically have a T1-weighted or balanced contrast while providing T2-weighted contrast is more challenging.…”

Advancing the frontiers of MR-guided radiotherapy for pancreatic cancer

“…Therefore, improving image quality for online treatment adaptation, and tailoring sequences to the specific tumor site of interest should be a continuous area of research in MR-guided radiotherapy. [147][148][149] The PROPELLER sequence from Chapter 2 remains the prime candidate to be the nextgeneration MRI sequence for online adaptive planning. Its superior visual quality is obvious, it can be acquired out-of-the-box, and upcoming software updates will ensure geometric correction in 3D for this M2D scan.…”