Anatomical deformation due to horizontal rotation: towards gantry-free radiation therapy

Authors

Jarryd Buckley, University of Wollongong, Ingham Institute for Applied Medical ResearchFollow
Robba Rai, Ingham Institute for Applied Medical Research, South West Sydney Local Health District
Gary P. Liney, University of Wollongong, University of New South Wales, South West Sydney Local Health District, Ingham Institute for Applied Medical ResearchFollow
Jason A. Dowling, University of Wollongong, University of New South Wales, CSIROFollow
Lois C. Holloway, University of Wollongong, University of New South Wales, South West Sydney Local Health District, Ingham Institute for Applied Medical ResearchFollow
Peter E. Metcalfe, University of Wollongong, Ingham Institute for Applied Medical ResearchFollow
Paul J. Keall, Ingham Institute for Applied Medical Research, University of SydneyFollow

RIS ID

138720

Publication Details

Buckley, J. G., Rai, R., Liney, G. P., Dowling, J. A., Holloway, L. C., Metcalfe, P. E. & Keall, P. J. (2019). Anatomical deformation due to horizontal rotation: towards gantry-free radiation therapy. Physics in Medicine and Biology, 64 (17), 175014-1-175014-12.

Abstract

Gantry-free radiation therapy systems may be simpler and more cost effective, particularly for MRI-guided photon or hadron therapy. This study aims to understand and quantify anatomical deformations caused by horizontal rotation with scan sequences sufficiently short to facilitate integration into an MRI-guided workflow. Rigid and non-rigid pelvic deformations due to horizontal rotation were quantified for a cohort of 8 healthy volunteers using a bespoke patient rotation system and a clinical MRI scanner. For each volunteer a reference scan was acquired at 0° followed by sequential faster scans in 45° increments through to 360°. All fast scans were registered to the 0° image via a three-step process: first, images were aligned using MR visible couch markers. Second, the scans were pre-processed then rigidly registered to the 0° image. Third, the rigidly registered scans were non-rigidly registered to the 0° image to assess soft tissue deformation. The residual differences after rigid and non-rigid registration were determined from the transformation matrix and the deformation vector field, respectively. The rigid registration yielded mean rotations of  ⩽2.5° in all cases. The average 3D translational magnitudes range was 5.8  ±  2.9 mm-30.0  ±  11.0 mm. Translations were most significant in the left-right (LR) direction. Smaller translations were observed in the anterior-posterior (AP) and superior-inferior (SI) directions. The maximum deformation magnitudes range was: 10.0  ±  0.9 mm-28.0  ±  2.8 mm and average deformation magnitudes range: 2.3  ±  0.6 mm-7.5  ±  1.0 mm. Average non-rigid deformation magnitude was correlated with BMI (correlation coefficient 0.84, p   =  0.01). Rigid pelvic deformations were most significant in the LR direction but could be accounted for with on-line adjustments. Non-rigid deformations can be significant and will need to be accounted for in order to facilitate the delivery of gantry-free therapy with an automated patient rotation system.