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. 2021 Oct 16:20:34-39.
doi: 10.1016/j.phro.2021.10.001. eCollection 2021 Oct.

Optimisation and validation of an integrated magnetic resonance imaging-only radiotherapy planning solution

Laura M O'Connor  1   2 , Kate Skehan  1 , Jae H Choi  3 , John Simpson  1   3 , Jarad Martin  1   3 , Helen Warren-Forward  2 , Jason Dowling  4   5 , Peter Greer  1   3
Affiliations

Optimisation and validation of an integrated magnetic resonance imaging-only radiotherapy planning solution

Laura M O'Connor et al. Phys Imaging Radiat Oncol. .

Abstract

Background and purpose: Magnetic resonance imaging (MRI)-only treatment planning is gaining in popularity in radiation oncology, with various methods available to generate a synthetic computed tomography (sCT) for this purpose. The aim of this study was to validate a sCT generation software for MRI-only radiotherapy planning of male and female pelvic cancers. The secondary aim of this study was to improve dose agreement by applying a derived relative electron and mass density (RED) curve to the sCT.

Method and materials: Computed tomography (CT) and MRI scans of forty patients with pelvic neoplasms were used in the study. Treatment plans were copied from the CT scan to the sCT scan for dose comparison. Dose difference at reference point, 3D gamma comparison and dose volume histogram analysis was used to validate the dose impact of the sCT. The RED values were optimised to improve dose agreement by using a linear plot.

Results: The average percentage dose difference at isocentre was 1.2% and the mean 3D gamma comparison with a criteria of 1%/1 mm was 84.0% ± 9.7%. The results indicate an inherent systematic difference in the dosimetry of the sCT plans, deriving from the tissue densities. With the adapted REDmod table, the average percentage dose difference was reduced to -0.1% and the mean 3D gamma analysis improved to 92.9% ± 5.7% at 1%/1 mm.

Conclusions: CT generation software is a viable solution for MRI-only radiotherapy planning. The option makes it relatively easy for departments to implement a MRI-only planning workflow for cancers of male and female pelvic anatomy.

Keywords: DVH, dose volume histogram; HU, Hounsfield Unit; ICRU, International Commission on Radiation Units and Measurements; MRI only radiation therapy; Prostate cancer; RED, Relative electron density; Radiation therapy treatment planning; Radiotherapy; Rectal cancer; Synthetic CT; sCT, synthetic computed tomography.

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Conflict of interest statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Figures

Fig. 1
Fig. 1
Linear relationship between the mean isocentre dose differences for two fat tissue electron density values ±1 SD. The x-intercept represents the optimal electron density used for fat.
Fig. 2
Fig. 2
DVH results by structure for REDsCT and REDsCT,mod applied to sCT.
See this image and copyright information in PMC

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