Brain and Head-and-Neck MRI in Immobilization Mask: A Practical Solution for MR-Only Radiotherapy.

Stefano Mandija,Joost J C Verhoeff,Alessandro Sbrizzi,Rob H N Tijssen,Federico D'Agata,Jan J W Lagendijk,Robin J M Navest,Cornelis A T Van Den Berg,Enrica Seravalli,Marielle E P Philippens,Cornelis P J Raaijmakers

doi:10.3389/fonc.2019.00647

Stefano Mandija, Joost J C Verhoeff + Show 9 more

Open Access

https://doi.org/10.3389/fonc.2019.00647

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Abstract

In brain/head-and-neck radiotherapy (RT), thermoplastic immobilization masks guarantee reproducible patient positioning in treatment position between MRI, CT, and irradiation. Since immobilization masks do not fit in the diagnostic MR head/head-and-neck coils, flexible surface coils are used for MRI imaging in clinical practice. These coils are placed around the head/neck, in contact with the immobilization masks. However, the positioning of these flexible coils is technician dependent, thus leading to poor image reproducibility. Additionally, flexible surface coils have an inferior signal-to-noise-ratio (SNR) compared to diagnostic coils. The aim of this work was to create a new immobilization setup which fits into the diagnostic MR coils in order to enhance MR image quality and reproducibility. For this purpose, a practical immobilization setup was constructed. The performances of the standard clinical and the proposed setups were compared with four tests: SNR, image quality, motion restriction, and reproducibility of inter-fraction subject positioning. The new immobilization setup resulted in 3.4 times higher SNR values on average than the standard setup, except directly below the flexible surface coils where similar SNR was observed. Overall, the image quality was superior for brain/head-and-neck images acquired with the proposed RT setup. Comparable motion restriction in feet-head/left-right directions (maximum motion ≈1 mm) and comparable inter-fraction repositioning accuracy (mean inter-fraction movement 1 ± 0.5 mm) were observed for the standard and the new setup.

Highlights

In daily radiotherapy (RT) clinical practice, Magnetic Resonance Imaging (MRI) is a principal image modality [1, 2]
We investigate and compare SNR, image quality, motion restriction and reposition accuracy of the proposed setups with respect to the standard used in daily brain and head-and-neck RT
The standard RT brain (RT-B) and the standard head-andneck (RT-HN) setups consisting of an individualized fivepoints head-and-shoulder mask (Posicast; Civco Sinmed, Reeuwijk, The Netherlands) fixated to an in-house developed base plate (Figure 1, black arrows), which was positioned on the MRI flat table top

Summary

Introduction

In daily radiotherapy (RT) clinical practice, Magnetic Resonance Imaging (MRI) is a principal image modality [1, 2]. An essential requirement in RT is the reproducibility of patient positioning between MRI, CT, and irradiation fractions [5]. For this purpose, immobilization masks are currently used for brain and head-and-neck RT [6]. The use of immobilization masks ensures that the MRI and CT exams. Brain/Head-and-Neck Radiotherapy Setup are performed in the same treatment position (TP). This allows reproducible patient positioning, minimization of registration errors, and guarantee correct dose calculation, it leads to several disadvantages from an MRI imaging perspective

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