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Verification imaging in prostate MR-only radiotherapy: Are fiducial markers necessary?

Lookup NU author(s): Dr Rachel Pearson, JJ Wyatt

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This work is licensed under a Creative Commons Attribution 4.0 International License (CC BY 4.0).

Abstract

© 2024 The Authors. Purpose/objective: MR-only radiotherapy planning exploits the benefits of MRI soft-tissue delineation, whilst negating the registration inaccuracies caused by MRI CT fusion. Fiducial markers have conventionally been used in prostate radiotherapy to reduce on-treatment image matching variability. However, this is an invasive procedure for the patient, and presents technical difficulties in an MR-only pathway as fiducial markers are difficult to visualise on MRI. This study compares MR-CBCT soft-tissue matching to fiducial matching in an MR-only prostate pathway. Material/methods: Four therapeutic radiographers reviewed first fraction CBCTs for 25 patients. The CBCT was compared to the planning MRI, a T2 weighted sequence for the soft-tissue match and compared to a T1 weighted MRI sequence for the fiducial match. Inter-observer variability was quantified using the inter-observer error and 95 % limits of agreement from a modified Bland-Altman analysis. Accuracy of the soft-tissue match was quantified by calculating the difference from the fiducial match. Results: Limits of agreement on the MR soft-tissue match were 1.5 mm, 4.0 mm, 3.5 mm and fiducial match 2.5 mm, 3.6 mm, 2.5 mm (lateral, longitudinal, vertical). Inter-observer error (±standard deviation) on the MR soft-tissue match were 0.6(±0.5) mm, 1.8(±1.1) mm, 1.7(±0.7) mm and fiducial match 0.7(±1.1) mm, 1.1(±1.5) mm, 0.8(±0.7) mm (lateral, longitudinal, vertical). The difference of the soft-tissue match from the fiducial match was 0.3(±1.1) mm, −0.1(±2.7) mm, 0.1(±1.9) mm (lateral, longitudinal, vertical). Conclusion: MR-CBCT soft-tissue matching has similar accuracy and inter-observer variability as fiducial matching. This suggests fiducial markers are not necessary in an MR-only prostate radiotherapy pathway. Implications for practice: MR-only prostate radiotherapy does not require fiducial markers since MR-CBCT soft tissue matching can be used for IGRT.

Publication metadata

Author(s): Brooks-Pearson RL, Pearson RA, O'Connor L, Skehan K, Redding D, Wilkins E, Taylor S, Wyatt JJ

Publication type: Article

Publication status: Published

Journal: Radiography

Year: 2025

Volume: 31

Issue: 1

Pages: 333-340

Print publication date: 01/01/2025

Online publication date: 27/12/2024

Acceptance date: 11/12/2024

Date deposited: 06/01/2025

ISSN (print): 1078-8174

ISSN (electronic): 1532-2831

Publisher: W.B. Saunders Ltd

URL: https://doi.org/10.1016/j.radi.2024.12.010

DOI: 10.1016/j.radi.2024.12.010

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