A planning-based feasibility study of MR-Linac treatment for anal cancer radiation therapy

Drew Smith; Kellie Knight; Jenny Sim; Daryl Lim Joon; Farshad Foroudi; Vincent Khoo

doi:10.1016/j.meddos.2023.07.001

A planning-based feasibility study of MR-Linac treatment for anal cancer radiation therapy

Med Dosim. 2023;48(4):267-272. doi: 10.1016/j.meddos.2023.07.001. Epub 2023 Jul 26.

Authors

Drew Smith¹, Kellie Knight², Jenny Sim², Daryl Lim Joon³, Farshad Foroudi⁴, Vincent Khoo⁵

Affiliations

¹ Department of Radiation Oncology, Olivia Newton-John Cancer Wellness & Research Centre, Austin Health, Heidelberg, Australia; Department of Medical Imaging and Radiation Sciences, Monash University, Clayton, Australia. Electronic address: Drew.Smith@austin.org.au.
² Department of Medical Imaging and Radiation Sciences, Monash University, Clayton, Australia.
³ Department of Radiation Oncology, Olivia Newton-John Cancer Wellness & Research Centre, Austin Health, Heidelberg, Australia.
⁴ Department of Radiation Oncology, Olivia Newton-John Cancer Wellness & Research Centre, Austin Health, Heidelberg, Australia; Department of Medical Imaging and Radiation Sciences, Monash University, Clayton, Australia.
⁵ Department of Radiation Oncology, Olivia Newton-John Cancer Wellness & Research Centre, Austin Health, Heidelberg, Australia; Department of Medical Imaging and Radiation Sciences, Monash University, Clayton, Australia; Department of Medicine, University of Melbourne, Melbourne, Australia; Department of Clinical Oncology, The Royal Marsden NHS Foundation Trust, London, United Kingdom.

PMID: 37507334
DOI: 10.1016/j.meddos.2023.07.001

Abstract

The hybrid magnetic resonance image (MRI) scanner and radiation therapy linear accelerator (MR-Linac) has the potential to enhance clinical outcomes for anal cancer (AC) patients with improved soft tissue visualization and daily plan adaption but has planning and delivery limitations due to the incorporation of MRI. We aimed to identify if Elekta Unity MR-Linac-based radiation therapy is feasible for anal cancer. Ten prospectively enrolled AC patients treated with radical chemoradiotherapy were replanned for MR-Linac treatment using departmental planning criteria. For comparison, and to reduce interobserver variability, volumetric modulated arc radiation therapy (VMAT) plans were also created for each patient by the same single senior radiation therapist. Plans were compared using departmental dosimetric plan criteria, as well as conformity and homogeneity indices, monitor units (MUs) and measured plan delivery (beam-on) time. Results were deemed clinically acceptable. Target and organ at risk (OAR) doses were comparable between MR-Linac plans and VMAT plans, although PTV45Gy D98% coverage was compromised in 3 of 10 MR-Linac plans due to caudocranial length exceeding the limits of the MR-Linac. MR-Linac plans had lower MUs, median of 689.1 vs 849.65 (p = 0.002), but took over twice as long to deliver, 529.5s vs 224s (p = <0.0001) as VMAT plans. MR-Linac planning and treatment of AC is feasible for a subset of patients. The current physical limitations of the Elekta Unity system mean patients with large caudocranial elective PTV45Gy target volumes may not be covered dosimetrically to the required clinical standard. Longer image verification and treatment delivery times of the MR-Linac also mean patient selection and intrafractional IGRT are likely to be integral to ensuring high quality clinical outcomes in this rare cancer.

Keywords: Anus; Cancer; MR-Linac; Radiation therapy; Radiotherapy; VMAT.

MeSH terms

Anus Neoplasms* / radiotherapy
Feasibility Studies
Humans
Particle Accelerators
Radiotherapy Dosage
Radiotherapy Planning, Computer-Assisted / methods
Radiotherapy, Intensity-Modulated* / methods