A mask-compatible, radiolucent, 8-channel head and neck receive array for MRI-guided radiotherapy treatments and pre-treatment simulation

• Published in: Physics in medicine & biology 2022-07, Vol.67 (13), p.135006
• Main 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
• Format: Article
• Language: English
• Subjects: head and neck; mask-compatible; MR-linac; MRI-guided radiotherapy; MRI-simulation; radiolucent receive array
• ISSN: 0031-9155; 1361-6560
• DOI: 10.1088/1361-6560/ac6ebd

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 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 SNR 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.