Understanding the Benefit of Magnetic Resonance-guided Adaptive Radiotherapy in Rectal Cancer Patients: a Single-centre Study

M Ingle; I White; J Chick; H Stankiewicz; A Mitchell; H Barnes; T Herbert; S Nill; U Oelfke; R Huddart; B Ng-Cheng-Hin; S Hafeez; S Lalondrelle; A Dunlop; S Bhide

doi:10.1016/j.clon.2022.10.008

Understanding the Benefit of Magnetic Resonance-guided Adaptive Radiotherapy in Rectal Cancer Patients: a Single-centre Study

Clin Oncol (R Coll Radiol). 2023 Feb;35(2):e135-e142. doi: 10.1016/j.clon.2022.10.008. Epub 2022 Nov 3.

Authors

M Ingle¹, I White², J Chick³, H Stankiewicz³, A Mitchell³, H Barnes³, T Herbert³, S Nill⁴, U Oelfke⁴, R Huddart⁵, B Ng-Cheng-Hin³, S Hafeez⁵, S Lalondrelle⁵, A Dunlop³, S Bhide⁵

Affiliations

¹ The Royal Marsden Hospital NHS Trust, London, UK; The Institute of Cancer Research, London, UK. Electronic address: manasi.ingle@icr.ac.uk.
² Guys and St Thomas NHS Trust, London, UK.
³ The Royal Marsden Hospital NHS Trust, London, UK.
⁴ The Institute of Cancer Research, London, UK.
⁵ The Royal Marsden Hospital NHS Trust, London, UK; The Institute of Cancer Research, London, UK.

PMID: 36336579
DOI: 10.1016/j.clon.2022.10.008

Abstract

Aims: Neoadjuvant chemoradiotherapy followed by surgery is the mainstay of treatment for patients with rectal cancer. Standard clinical target volume (CTV) to planning target volume (PTV) margins of 10 mm are used to accommodate inter- and intrafraction motion of target. Treating on magnetic resonance-integrated linear accelerators (MR-linacs) allows for online manual recontouring and adaptation (MRgART) enabling the reduction of PTV margins. The aim of this study was to investigate motion of the primary CTV (CTVA; gross tumour volume and macroscopic nodes with 10 mm expansion to cover microscopic disease) in order to develop a simultaneous integrated boost protocol for use on MR-linacs.

Materials and methods: Patients suitable for neoadjuvant chemoradiotherapy were recruited for treatment on MR-linac using a two-phase technique; only the five phase 1 fractions on MR-linac were used for analysis. Intrafraction motion of CTVA was measured between pre-treatment and post-treatment MRI scans. In MRgART, isotropically expanded pre-treatment PTV margins from 1 to 10 mm were rigidly propagated to post-treatment MRI to determine overlap with 95% of CTVA. The PTV margin was considered acceptable if overlap was >95% in 90% of fractions. To understand the benefit of MRgART, the same methodology was repeated using a reference computed tomography planning scan for pre-treatment imaging.

Results: In total, nine patients were recruited between January 2018 and December 2020 with T3a-T4, N0-N2, M0 disease. Forty-five fractions were analysed in total. The median motion across all planes was 0 mm, demonstrating minimal intrafraction motion. A PTV margin of 3 and 5mm was found to be acceptable in 96 and 98% of fractions, respectively. When comparing to the computed tomography reference scan, the analysis found that PTV margins to 5 and 10 mm only acceptably covered 51 and 76% of fractions, respectively.

Conclusion: PTV margins can be reduced to 3-5 mm in MRgART for rectal cancer treatment on MR-linac within an simultaneous integrated boost protocol.

Keywords: Adaptive radiotherapy; MR-linac; MRI; rectal cancer.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Humans
Magnetic Resonance Imaging / methods
Magnetic Resonance Spectroscopy
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Radiotherapy, Image-Guided* / methods
Radiotherapy, Intensity-Modulated* / methods
Rectal Neoplasms* / diagnostic imaging
Rectal Neoplasms* / pathology
Rectal Neoplasms* / radiotherapy
Tomography, X-Ray Computed

Abstract

Publication types

MeSH terms

Grants and funding