Considerations for the clinical implementation of MRI-guided ART for H&N and lung cancers
Clough, Abigael Pitt, Eleanor Nelder, Claire L Benson, Rebecca McDaid, Lisa Whiteside, Lee Davies, Lucy Parker, Jacqui Awofisoye, T. Freear, Linnea
Clough, Abigael
Pitt, Eleanor
Nelder, Claire L
Benson, Rebecca
McDaid, Lisa
Whiteside, Lee
Davies, Lucy
Parker, Jacqui
Awofisoye, T.
Freear, Linnea
Citations
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Abstract
Purpose or Objective
Clinical commissioning of complex treatment indications on the MR Linac (MRL) requires several considerations: selecting
the optimal image sequences for planning and treatment delivery, ensuring users are competent in MR image registrations,
adaptation strategy and identification of triggers for adaptation are identified. This work describes the steps taken to
select MRI sequences and validate inter-observer registration prior to the clinical implementation of MR-guided adaptive
radiotherapy for oropharyngeal (H&N) and lung cancers.
Materials and Methods
Prior to the clinical implementation on the MRL for H&N and lung cancer, patient volunteers were recruited to an
institutionally approved imaging study (PRIMER). Image quality was assessed using visual guided assessments (VGAs) to
determine the most suitable tissue weighting for daily image registration. Three observers (1 oncologist and 2
radiographers) independently scored visibility of the tumour and pre-determined organs at risk (OARs) on vendor provided
T1 and T2 weighted images for 10 H&N and 6 lung patients. Nine radiographers completed offline MRI to CT and MRI to MRI
rigid registrations in Monaco v5.11.02 (Elekta AB, Sweden) for 5 H&N and 4 lung patients, using bony and soft tissue matching
strategies. The resulting translations, registration time and confidence scores were recorded using a 5 point Likert scale.
Descriptive statistics were calculated in Microsoft Excel.
Results
The VGA scores demonstrated tumour visibility was unclear/not visible for all lung images, however, the lungs (44% vs 33%)
bronchial tree (67% vs 44%) and trachea (89% vs 78%) were more visible on T2 than T1. In the R/L (-0.002 vs -0.15,) and A/P
(0.05 vs 0.19) directions T2-CT mean inter-observer variation were lower than those for T1-CT for soft tissues matches. The
mean time taken for offline T1-CT and T2-CT image registration was 4 minutes. These times are longer than expected for
online registration which to date has averaged at 2:42 minutes. For H&N, T1 and T2 images have similar tumour visualisation
(58% vs 53%). T1 sequences demonstrated superior nodal (61%vs 41%), optic nerve (100% vs 38%) and parotid (91% vs 44%)
visualisation. Mean inter-observer variation and SD for T1-CT and T2-CT registration methods were greatest in the SI
directions for both bony and soft tissue matches with the greatest variation present for T2-CT. Radiographers had a 75%
agreement on whether to soft tissue or bony match on T1-CT image registration compared to 59% for T2-CT.The mean time
was identical for the T1-CT and T2-CT at 5 minutes, however online this has been significantly reduced to an average of 2:16 minutes Conclusion
Using systematic evaluations the interdisciplinary team was able to identify and agree on sequence selection for H&N (T1)
and lung (T2). This process will be used moving forward to future MRL indications (e.g., pancreas). Work continues outside
the vendor provided workflow to further optimise imaging.
Affiliation
Description
Date
2022
Publisher
Collections
Keywords
Type
Meetings and Proceedings
Citation
Clough A, Pitt E, Nelder C, Benson R, McDaid L, Whiteside L, et al. Considerations for the clinical implementation of MRI-guided ART for H&N and lung cancers. Radiotherapy and Oncology. 2022 May;170:S364-S6. PubMed PMID: WOS:000806764200014.