Gross tumour volume (GTV) delineation on magnetic resonance imaging (MRI), for stage III lung cancer: consensus recommendations needed to ensure contouring consistency
van Herk, Marcel
AffiliationClinical Oncology, The Royal Marsden NHS Foundation Trust, London,
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AbstractIntroduction: MRI in the context of the radiotherapy (RT) planning workflow for locally advanced lung cancer (LALC) presents a number of advantages. MRI provides better soft tissue definition potentially reducing inter-observer contouring variability of GTV, allowing tighter margins. This could facilitate the development of intensified adaptive strategies. Defining the GTV on MRI in lung cancer is novel. Prior to inter-observer variability assessment, training of clinicians is paramount. Methods: Two training workshops were organised. The first workshop was web-based, led by an MRI radiologist. Fifteen radiation oncologists participated, from 9 centres internationally. Eight LALC cases were chosen to cover various anatomical scenarios including chest wall and mediastinal invasion, and superior sulcus tumours. The second workshop was face-to-face. The most challenging cases from the web-based workshop were reviewed, this time with applied contours checked by the same MRI radiologist. Subsequently, 10 radiation oncologists delineated the GTV on 3 separate cases. Delineation was performed on T1-weighted mid-position 4D radial VIBE MRI, registered with the mid-position 4DCT, PET CT and MRI sequences, including T2 TSE and TSE DIXON. These contours were compared with those produced by an MRI radiologist. Results: There are discrepancies in GTV delineation between MRI radiologists and radiation oncologists, particularly at sites of tumour invasion causing pleural reaction or bone oedema (Fig. 1). This demonstrates that recommendations for MRI GTV delineation must be developed collaboratively between both disciplines. Further work will involve contouring of 9 LALC cases on MRI, by a 'pair' of an MRI radiologist and a radiation oncologist from at least 8 international centres. These will be compared against blinded CT/ PET-CT contouring, and discussed, to produce recommendations for GTV delineation on MRI. Conclusion: Although GTV contouring on MRI is challenging it may provide better contrast information compared to CT. Novel MRI-guided adaptive strategies must be optimised collaboratively between MRI radiologists and radiation oncologists.
CitationShiarli A, Brown S, Dubec M, Bainbridge H, Koh D, Lalezari F, et al. Gross tumour volume (GTV) delineation on magnetic resonance imaging (MRI), for stage III lung cancer: consensus recommendations needed to ensure contouring consistency. Lung Cancer. 2019;127:S77-S.
TypeMeetings and Proceedings