Assessing the impact of magnetic resonance treatment simulation (MRSIM) on target volume delineation and dose to organs at risk for oropharyngeal radiotherapy

Abstract

Introduction: Assessing the use of a radiation therapy (RT) planning MRI performed in the treatment position (pMRI) on target volume delineation and effect on organ at risk dose for oropharyngeal cancer patients planned with diagnostic MRI (dMRI) and CT scan. Methods: Diagnostic MRI scans were acquired for 26 patients in a neutral patient position using a 3T scanner (dMRI). Subsequent pMRI scans were acquired on the same scanner with a flat couch top and the patient in their immobilisation mask. Each series was rigidly registered to the patients planning CT scan and volumes were first completed with the CT/dMRI. The pMRI was then made available for volume modification. For the group with revised volumes, two IMRT plans were developed to demonstrate the impact of the modification. Image and registration quality was also evaluated. Results: The pMRI registration led to the modification of target volumes for 19 of 26 participants. The pMRI target volumes were larger in absolute volume resulting in reduced capacity for organ sparing. Predominantly, modifications occurred for the primary gross tumour volume (GTVp) with a mean Dice Similarity Coefficient (DSC) of 0.7 and the resulting high risk planning target volume, a mean DSC of 0.89. Both MRIs scored similarly for image quality, with the pMRI demonstrating improved registration quality and efficiency. Conclusions: A pMRI provides improvement in registration efficiency, quality and a higher degree of oncologist confidence in target delineation. These results have led to a practice change within our department, where a pMRI is acquired for all eligible oropharyngeal cancer patients.

MRI sequence optimisation methods to identify cranial nerve course for radiotherapy planning

“…For patients receiving intracranial treatment, the isotropic nature of the entire MRI protocol allowed for the use of a 20‐channel head and neck coil, or a 32‐channel head coil for image acquisition. For patients who were receiving treatment to the head region, extending outside of the cranium and into the neck, neck flexion caused difficulty in the rigid registration process between scans, therefore the radiation therapy treatment position had to be accounted for 1 …”

“…For patients who were receiving treatment to the head region, extending outside of the cranium and into the neck, neck flexion caused difficulty in the rigid registration process between scans, therefore the radiation therapy treatment position had to be accounted for. 1 …”

“…For patients who were receiving treatment to the head region, extending outside of the cranium and into the neck, neck flexion caused difficulty in the rigid registration process between scans, therefore the radiation therapy treatment position had to be accounted for. 1 The region of interest and cranial nerves of interest were requested by the treating radiation oncologist. The first 12 patients identified were used for the initial validation phase for radiation oncologist feedback and sequence optimisation, before routine clinical application.…”

“…It is common practice to import diagnostic images to radiation therapy planning systems, however, diagnostic images can result in suboptimal image fusion due to differences in patient position and inherent distortions in diagnostic scans, particularly in the translation of small structures. 1 Deformable image registration techniques are currently utilised clinically to overcome these image registration obstacles. However, if appropriate deformable software is unavailable to a clinic, or in the absence of reference CT, such as in the case of MRI-based treatment planning, it is important to investigate the adaptation of MRI protocols This is an open access article under the terms of the Creative Commons Attribution-NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes.…”

“…With the advent of MRI simulators and MRI LINACS, it has become necessary to understand the concepts of MRI and adaption for radiation treatments. It is common practice to import diagnostic images to radiation therapy planning systems, however, diagnostic images can result in suboptimal image fusion due to differences in patient position and inherent distortions in diagnostic scans, particularly in the translation of small structures 1 . Deformable image registration techniques are currently utilised clinically to overcome these image registration obstacles.…”