Feasibility of MR-only radiation planning for hypofractionated stereotactic radiotherapy of schwannomas using non-coplanar volumetric modulated arc therapy
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To compare the dose calculation accuracy of plans done on a CT density-assigned MR image set for hypofractionated stereotactic radiotherapy (HSRT) using volumetric modulated radiation therapy containing non-coplanar beams.
Eighteen patients diagnosed with schwannoma treated with HSRT were selected retrospectively. These patients underwent planning CT (pCT) for radiation therapy (RT) and contrast-enhanced three-dimensional fast-spoiled gradient-echo image (3D FSPGR) to assist tumor delineation. CTplan is plan done on pCT. The structures body, bone, and air are contoured exclusively on MR image and assigned Hounsfield units of 25, + 1000, and − 1000, respectively. This is termed as MRCT. After registration, original plans from pCT are pasted on the MRCT. Dose calculation is done in two ways: (1) with preset MU values (DDC) and (2) with optimization (OPT_DC). Conformity indices and Dmax and D0.5cc of brainstem, gamma agreement index and correlation coefficient are analyzed. ANOVA test is carried out to find the significance of difference between plans.
The mean deviations of Dmax and D0.5cc of brainstem for CTplan versus DDC are 2.49% and 1.45% respectively. The mean deviations of Dmax and D0.5cc of brainstem for CTplan versus OPT_DC are − 1.56% and − 1.97%, respectively. Mean deviations of conformity index for DDC and OPT_DC are 0.84% and 0.89%, respectively. No significant difference was found with ANOVA test.
Results show that there is no difference between plans generated with actual CT data and MRCT data. Thus MR scans could be employed for radiation planning provided the verification image is available. This gives us confidence to reduce treatment margins where image registration process is avoided.
KeywordsMRI in radiation planning MRCT FSPGR MR image Hypofractionated stereotactic radiotherapy Volumetric modulated radiation therapy
Compliance with ethical standards
Conflict of interest
All authors contributed to this study declare that they have no conflict of interest with respect to the manuscript.
Institutional scientific and ethics board has approved this study. This article does not contain any studies with human participants performed by any of the authors.
The informed consent has been waived off by the ethics board of the institute considering this as a retrospective study.
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