Feasibility of reduced PTV margins in magnetic resonance image-guided online adaptive radiotherapy for bladder cancer: a personalised approach.
- 1The Royal Marsden NHS Foundation Trust, London, United Kingdom.
- 2The Institute of Cancer Research/The Royal Marsden NHS Foundation Trust, London, United Kingdom.
- 3Joint Department of Physics at the Royal Marsden and The Institute of Cancer Research, United Kingdom.
Abstract
Introduction
Bladder MRI-guided online adaptive radiotherapy (MRIgART) has enabled a reduction in planning target volume (PTV) margins, reducing normal tissue irradiation. Yet, further margin reduction is limited due to workflow duration and intra-fractional bladder variation. This study reports the feasibility of a 5 mm isotropic PTV in whole bladder MRIgART, 55 Gy in 20 fractions daily, and 36 Gy in 6 fractions weekly, with a personalised approach to margin expansion.Methods
Patients voided their bladders prior to treatment. Following setup, a daily MRI (MRDAILY) was acquired, and an adaptive workflow was performed. An MRI was acquired during delivery to coincide with treatment completion (MRPOST). Time from MRDAILY to MRPOST was recorded. Offline, target coverage of the clinical target volume (CTV) was visually monitored by comparing MRDAILY and MRPOST images. Images were reviewed by the radiation oncologist (RO) if the CTV was outside of the PTV on the MRPOST. Under RO discretion, margins were personalised to the minimum margin that would have encompassed the CTV and applied online for subsequent fractions. In retrospective analysis, MRPOST CTVs were recontoured, and the adaptive plan recalculated. CTV coverage was deemed acceptable if V95% ≥ 95%. If this objective was not met, the gross tumour volume (GTV) was delineated and the dose reported; coverage was deemed acceptable if GTV V95% ≥ 95%.Results
A total of 138 fractions from ten patients were analysed. Median (interquartile range) workflow time was 25.6 (20.8-30.7) minutes. PTV margins were personalised for 31 fractions in three patients. 119 MRPOST images were available for analysis. CTV coverage was achieved in 94% (112/119) of fractions. Where the CTV mandatory objectives were missed (6%; 7/119 fractions), GTV coverage was acceptable in 6 of the 7 fractions.Conclusion
Whole bladder MRIgART with 5 mm isotropic PTV margins with a personalised approach to margin expansion is feasible in achieving acceptable CTV coverage.
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BibTeX
@article{williams2026feasibility,
title = {{Feasibility of reduced PTV margins in magnetic resonance image-guided online adaptive radiotherapy for bladder cancer: a personalised approach.}},
author = {Bethany Williams and Saleh Sandoughdaran and Joan Chick and Alex Dunlop and Trina Herbert and Robert Huddart and Adam Mitchell and Simeon Nill and Shaista Hafeez and Helen A McNair},
journal = {Clinical and translational radiation oncology},
year = {2026},
month = oct,
doi = {10.1016/j.ctro.2026.101321},
url = {https://europepmc.org/article/MED/42926875},
note = {CC BY},
}
RIS
TY - JOUR
TI - Feasibility of reduced PTV margins in magnetic resonance image-guided online adaptive radiotherapy for bladder cancer: a personalised approach.
AU - Bethany Williams
AU - Saleh Sandoughdaran
AU - Joan Chick
AU - Alex Dunlop
AU - Trina Herbert
AU - Robert Huddart
AU - Adam Mitchell
AU - Simeon Nill
AU - Shaista Hafeez
AU - Helen A McNair
PY - 2026
DA - 2026/10/10
JO - Clinical and translational radiation oncology
DO - 10.1016/j.ctro.2026.101321
UR - https://europepmc.org/article/MED/42926875
AB - Introduction Bladder MRI-guided online adaptive radiotherapy (MRIgART) has enabled a reduction in planning target volume (PTV) margins, reducing normal tissue irradiation. Yet, further margin reduction is limited due to workflow duration and intra-fractional bladder variation. This study reports the feasibility of a 5 mm isotropic PTV in whole bladder MRIgART, 55 Gy in 20 fractions daily, and 36 Gy in 6 fractions weekly, with a personalised approach to margin expansion.Methods Patients voided their bladders prior to treatment. Following setup, a daily MRI (MRDAILY) was acquired, and an adaptive workflow was performed. An MRI was acquired during delivery to coincide with treatment completion (MRPOST). Time from MRDAILY to MRPOST was recorded. Offline, target coverage of the clinical target volume (CTV) was visually monitored by comparing MRDAILY and MRPOST images. Images were reviewed by the radiation oncologist (RO) if the CTV was outside of the PTV on the MRPOST. Under RO discretion, margins were personalised to the minimum margin that would have encompassed the CTV and applied online for subsequent fractions. In retrospective analysis, MRPOST CTVs were recontoured, and the adaptive plan recalculated. CTV coverage was deemed acceptable if V95% ≥ 95%. If this objective was not met, the gross tumour volume (GTV) was delineated and the dose reported; coverage was deemed acceptable if GTV V95% ≥ 95%.Results A total of 138 fractions from ten patients were analysed. Median (interquartile range) workflow time was 25.6 (20.8-30.7) minutes. PTV margins were personalised for 31 fractions in three patients. 119 MRPOST images were available for analysis. CTV coverage was achieved in 94% (112/119) of fractions. Where the CTV mandatory objectives were missed (6%; 7/119 fractions), GTV coverage was acceptable in 6 of the 7 fractions.Conclusion Whole bladder MRIgART with 5 mm isotropic PTV margins with a personalised approach to margin expansion is feasible in achieving acceptable CTV coverage.
SN - 2405-6308
ER -