The first patients treated with MR-CBCT soft-tissue matching in a MR-only prostate radiotherapy pathway

J J Wyatt; R A Pearson; J Frew; C Walker; N Richmond; M Wilkinson; K Wilkes; S Driver; S West; P Karen; R L Brooks-Pearson; D Ainslie; E Wilkins; H M McCallum

doi:10.1016/j.radi.2023.01.015

The first patients treated with MR-CBCT soft-tissue matching in a MR-only prostate radiotherapy pathway

Radiography (Lond). 2023 Mar;29(2):347-354. doi: 10.1016/j.radi.2023.01.015. Epub 2023 Feb 1.

Authors

J J Wyatt¹, R A Pearson², J Frew³, C Walker³, N Richmond³, M Wilkinson³, K Wilkes³, S Driver³, S West³, P Karen³, R L Brooks-Pearson³, D Ainslie³, E Wilkins³, H M McCallum²

Affiliations

¹ Northern Centre for Cancer Care, Newcastle Upon Tyne Hospitals NHS Foundation Trust, Newcastle, UK; Translational and Clinical Research Institute, Newcastle University, Newcastle, UK. Electronic address: jonathanwyatt@nhs.net.
² Northern Centre for Cancer Care, Newcastle Upon Tyne Hospitals NHS Foundation Trust, Newcastle, UK; Translational and Clinical Research Institute, Newcastle University, Newcastle, UK.
³ Northern Centre for Cancer Care, Newcastle Upon Tyne Hospitals NHS Foundation Trust, Newcastle, UK.

PMID: 36736147
DOI: 10.1016/j.radi.2023.01.015

Abstract

Introduction: Magnetic Resonance (MR)-only radiotherapy for prostate cancer has previously been reported using fiducial markers for on-treatment verification. MR-Cone Beam Computed Tomography (CBCT) soft-tissue matching does not require invasive fiducial markers and enables MR-only treatments to other pelvic cancers. This study evaluated the first clinical implementation of MR-only prostate radiotherapy using MR-CBCT soft-tissue matching.

Methods: Twenty prostate patients were treated with MR-only radiotherapy using a synthetic (s)CT-optimised plan with MR-CBCT soft-tissue matching. Two MR sequences were acquired: small Field Of View (FOV) for target delineation and large FOV for organs at risk delineation, sCT generation and on-treatment verification. Patients also received a CT for validation. The prostate was independently contoured on the small FOV MR, copied to the registered CT and modified if there were MR-CT soft-tissue alignment differences (MR-CT volume). This was compared to the MR-only volume with a paired t-test. The treatment plan was recalculated on CT and the doses compared. Independent offline CT-CBCT matches for 5/20 fractions were performed by three therapeutic radiographers using the MR-only contours and compared to the online MR-CBCT matches using two one-sided paired t-tests for equivalence within ±1 mm.

Results: The MR-only volumes were significantly smaller than MR-CT (p = 0.003), with a volume ratio 0.92 ± 0.02 (mean ± standard error). The sCT isocentre dose difference to CT was 0.2 ± 0.1%. MR-CBCT soft-tissue matching was equivalent to CT-CBCT (p < 0.001), with differences of 0.1 ± 0.2 mm (vertical), -0.1 ± 0.2 mm (longitudinal) and 0.0 ± 0.1 mm (lateral).

Conclusions: MR-only radiotherapy with soft-tissue matching has been successfully clinically implemented. It produced significantly smaller target volumes with high dosimetric and on-treatment matching accuracy.

Implications for practice: MR-only prostate radiotherapy can be safely delivered without using invasive fiducial markers. This enables MR-only radiotherapy to be extended to other pelvic cancers where fiducial markers cannot be used.

Keywords: Cone beam computed tomography; Image guided radiation therapy; MR-Only radiotherapy planning; Magnetic resonance imaging; Prostate cancer; Radiotherapy.

MeSH terms

Humans
Magnetic Resonance Spectroscopy
Male
Pelvic Neoplasms*
Prostate / diagnostic imaging
Radiotherapy Planning, Computer-Assisted / methods
Spiral Cone-Beam Computed Tomography*