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. 2019 May;124(5):400-407.
doi: 10.1007/s11547-018-0981-5. Epub 2018 Dec 19.

Feasibility of MR-only radiation planning for hypofractionated stereotactic radiotherapy of schwannomas using non-coplanar volumetric modulated arc therapy

Arivarasan Ilamurugu  1   2 , Anu Radha Chandrasekaran  3 , Anantharaman Ayyalusamy  4 , Subramanian Shanmugam  4 , Ramasubramanian Velayudham  3 , Gautham Reddy KattaCharu  4 , Shyama Prasanna Satpathy  4
Affiliations

Feasibility of MR-only radiation planning for hypofractionated stereotactic radiotherapy of schwannomas using non-coplanar volumetric modulated arc therapy

Arivarasan Ilamurugu et al. Radiol Med. 2019 May.

Abstract

Purpose: 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.

Methods: 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.

Results: 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.

Conclusion: 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.

Keywords: FSPGR MR image; Hypofractionated stereotactic radiotherapy; MRCT; MRI in radiation planning; Volumetric modulated radiation therapy.

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