Evaluating the repeatability and set-up sensitivity of a large field of view distortion phantom and software for magnetic resonance-only radiotherapy. (April 2018)

• Record Type: Journal Article
• Authors: Wyatt, Jonathan; Hedley, Stephen; Johnstone, Emily; Speight, Richard; Kelly, Charles; Henry, Ann; Short, Susan; Murray, Louise; Sebag-Montefiore, David; McCallum, Hazel
• Is Part Of: Physics and imaging in radiation oncology. Volume 6(2018)
• Page Start: 31
• Page End: 38
• Publication Date: 2018-04
• Subjects: Geometric distortion -- Magnetic resonance imaging -- Radiotherapy -- MR-only radiotherapy planning; Radiotherapy -- Periodicals; Radiation dosimetry -- Periodicals; Cancer -- Imaging -- Periodicals; Oncology -- Periodicals; 615.842
• DOI: 10.1016/j.phro.2018.04.005
• Languages: English
• ISSNs: 2405-6316

Abstract

Abstract: Background and purpose: Magnetic Resonance (MR)-only radiotherapy requires geometrically accurate MR images over the full scanner Field of View (FoV). This study aimed to investigate the repeatability of distortion measurements made using a commercial large FoV phantom and analysis software and the sensitivity of these measurements to small set-up errors. Materials and methods: Geometric distortion was measured using a commercial phantom and software with 2D and 3D acquisition sequences on three different MR scanners. Two sets of repeatability measurements were made: three scans acquired without moving the phantom between scans (single set-up) and five scans acquired with the phantom re-set up in between each scan (repeated set-up). The set-up sensitivity was assessed by scanning the phantom with an intentional 1 mm lateral offset and independently an intentional 1° rotation. Results: The mean standard deviation of distortion for all phantom markers for the repeated set-up scans was < 0.4 mm for all scanners and sequences. For the 1 mm lateral offset scan 90 % of the markers agreed within two standard deviations of the mean of the repeated set-up scan (median of all scanners and sequences, range 78%–93%). For the 1° rotation scan, 80% of markers agreed within two standard deviations of the mean (range 69%–93%). Conclusions: Geometric distortion measurements using a commercial phantom and associated software appear repeatable, although with some sensitivity to set-up errors. This suggests the phantom and software are appropriate for commissioning a MR-only radiotherapy workflow.