☆ 4.7 Article

Online adaptive MR-guided radiotherapy for rectal cancer; feasibility of the workflow on a 1.5T MR-linac: clinical implementation and initial experience

RADIOTHERAPY AND ONCOLOGY (2021)

Journal

RADIOTHERAPY AND ONCOLOGY

Volume 154, Issue -, Pages 172-178

Publisher

ELSEVIER IRELAND LTD

DOI: 10.1016/j.radonc.2020.09.024

Keywords

Radiotherapy; Rectal cancer; Magnetic resonance imaging; Image-guided radiation; Neoadjuvant therapy

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Abstract

This study evaluates the feasibility and implementation of MR-guided radiotherapy for rectal cancer on a 1.5T MR-linac. Results show that daily online adaptation of the CTV can reduce margins effectively and achieve good treatment outcomes. The treatment process takes about 48 minutes per fraction.

Background and purpose: Daily online adaptation of the clinical target volume (CTV) using MR-guided radiotherapy enables margin reduction of the planning target volume (PTV). This study describes the implementation and initial experience of MR-guided radiotherapy on the 1.5T MR-linac and evaluates treatment time, patient compliance, and target coverage, including an initial assessment of margin reduction. Materials and methods: Patients were treated on a 1.5T MR-linac (7MV, FFF). At each fraction a 3D T2 weighted (T2w) MR-sequence was acquired on which the CTV was adapted after a deformable registration of the contours from the pre-planning CT scan. Based on the new contours a full online replanning was done after which a new 3D T2w MR-sequence was acquired for position verification. A 5 field Intensity Modulated Radiotherapy (IMRT) plan was delivered. Results: Forty-three patients with rectal cancer were treated with 25 Gy in 5 fractions of which 18 with reduced margins. In total, 204 of 215 fractions were delivered on the MR-linac all of which obtained a clinically acceptable treatment plan. Median in-room time per fraction was 48 min (interquartile range 8). No fractions were canceled or interrupted because of patient intolerance. CTV coverage after margin reduction was good on all post-treatment scans but one due to passing gas. Conclusion: MR-guided radiotherapy using daily full online recontouring and replanning on a 1.5T MR-linac for rectal cancer is feasible and currently takes about 48 min per fraction. (C) 2021 The Authors. Published by Elsevier B.V.

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Clinical Applications of Magnetic Resonance-Guided Radiotherapy: A Narrative Review

Colton Ladbury, Arya Amini, Amanda Schwer, An Liu, Terence Williams, Percy Lee

Summary: Magnetic resonance-guided radiotherapy (MRgRT) combines an onboard MRI scanner with radiation delivery technology, enabling real-time low-field or high-field MRI acquisition and improving soft tissue delineation, adaptive treatment, and motion management. Research has shown that MRgRT can effectively shrink treatment margins, decrease toxicity in certain cancers, and improve oncologic outcomes in others, while also enabling clear soft tissue delineation and gating for specific indications. The use of MRgRT has the potential to significantly improve patient outcomes and quality of life. This narrative review aims to discuss the rationale for MRgRT, current and future technology, existing studies, and future directions and challenges associated with the advancement of MRgRT.

CANCERS (2023)