A mask-compatible, radiolucent, 8-channel head and neck receive array for MRI-guided radiotherapy treatments and pre-treatment simulation. (7th July 2022)

• Record Type: Journal Article
• Authors: Zijlema, Stefan E; Breimer, Wico; Gosselink, Mark W J M; Bruijnen, Tom; Arteaga de Castro, Catalina S; Tijssen, Rob H N; Lagendijk, Jan J W; Philippens, Marielle E P; van den Berg, Cornelis A T
• Is Part Of: Physics in medicine & biology. Volume 67:Number 13(2022)
• Publication Date: 2022-07-07
• Subjects: MRI-guided radiotherapy -- mask-compatible -- head and neck -- radiolucent receive array -- MR-linac -- MRI-simulation; Biophysics -- Periodicals; Medical physics -- Periodicals; 610.153
• DOI: 10.1088/1361-6560/ac6ebd
• Languages: English
• ISSNs: 0031-9155

Abstract

Abstract: Immobilization masks are used to prevent patient movement during head and neck (H&N) radiotherapy. Motion restriction is beneficial both during treatment, as well as in the pre-treatment simulation phase, where magnetic resonance imaging (MRI) is often used for target definition. However, the shape and size of the immobilization masks hinder the use of regular, close-fitting MRI receive arrays. In this work, we developed a mask-compatible 8-channel H&N array that consists of a single-channel baseplate, on which the mask can be secured, and a flexible 7-channel anterior element that follows the shape of the mask. The latter uses high impedance coils to achieve its flexibility and radiolucency. A fully-functional prototype was manufactured, its radiolucency was characterized, and the gain in imaging performance with respect to current clinical setups was quantified. Dosimetry measurements showed an overall dose change of −0.3%. Small, local deviations were up to −2.7% but had no clinically significant impact on a full treatment plan, as gamma pass rates (3%/3 mm) only slightly reduced from 97.9% to 97.6% (clinical acceptance criterion: ≥95%). The proposed H&N array improved the imaging performance with respect to three clinical setups. The H&N array more than doubled (+123%) and tripled (+246%) the signal-to-noise ratio with respect to the clinical MRI-simulation and MR-linac setups, respectively. G -factors were also lower with the proposed H&N array. The improved imaging performance resulted in a clearly visible signal-to-noise ratio improvement of clinically used TSE and DWI acquisitions. In conclusion, the 8-channel H&N array improves the imaging performance of MRI-simulation and MR-linac acquisitions, while dosimetry suggests that no clinically significant dose changes are induced.