Strengthening the weakest link: improving tumour definition Marianne C Aznar marianne.aznar@manchester.ac.uk University of Manchester / The Christie NHS Clinical Trial Service Unit, University of Oxford @RT_physics
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The weakest link Fiorino R&O 1998
Uncertainties today in the treatment chain: an example Delineation ~ 3 mm (systematic) Residual set-up error ~ 2 mm (assuming daily CBCT and appropriate fixation) Image registration ~ 1-2 mm Intrafraction motion (depending on site) ~ 1-10 mm (NB: not exhaustive!)
Inter-observer studies in the literature (2017) Prostate: Roach (PMB), Lee (Radiat Oncol J), Alasti (R&O), Rylander (R&O), Westendrop (Brachytherapy), Harvey (BJR), Lung: MacWilliam (R&O), Mercieca (R&O), Karki (IJROBP), Hou (J Med Im Radiat Onc) Breast: Al-Hammadi (Radiol Oncol), Francolini (R&O), Wennistg (R&O), Pogson (IJROBP)
Quantifying the problem then what? Measure of overlap Increased awareness of the problem Potential improvement after intervention Standard deviation Incorporate in margin recipe Aznar et Acta Oncol 2017
How do we proceed from here? Improving tumour definition Image-based techniques Other approaches Multi-modality Image processing Artefact reduction / contrast enhancement Guidelines Workshops Fiducials
Non-image based approaches
Workshop / education De Bari R&O 2017
Workshop / education Pre-teaching post-teaching GTV 0.82 0.85 CTV 0.68 0.89 De Bari R&O 2017
Delineating the tumour which isn t there : post-operative RT Sassowsky R&O 2017 use of EORTC guidelines in salvage RT for prostate cancer, SAKK 09/10 trial
MRI reduces variation in patients without clips However, clips are still superior Al Hammali Radiol Oncol 2017
Delineating the tumour which isn t there.
Hodgkin Lymphoma: using pretreatment/diagnostic imaging Pre-chemo PET/CT Planning CT Involved Node RT if optimal pre-chemo imaging (in RT position, etc ) Involved Site RT if differences (larger CTV volumes) Even with best pre-chemo imaging available, 3 mm interobserver variation in definition of CTV (Aznar Acta Oncol 2017)
Image based approaches
Multi-modality imaging Reduction of delineation variability by FDG-PET Steenbackers IJROBP 2006 CT SD 1.0cm PET SD 0.4cm Benefit of FDG-PET: Largest in regions of atelectasis
Multi modality imaging Karki IJROBP 2017: adding novel MRI sequences The Christie NHS provides Foundation Trust new information
Examples of tumor overlap between tumor defined from DWI (blue contour), 18F-FDG PET/MR (green contour), and T2-weighted MR (red contour). Jacob H. Rasmussen et al. J Nucl Med 2017;58:69-74 How do we handle discrepancies between different modalities??
Consistency/precision vs accuracy Pathology Phantoms Kovacs R&O 2017 Daisne Radiology 2004
Dual Energy CT Acquisitions: 120 kvp (standard), 80 kvp, 140 kvp (Siemens Somatom imar) Reconstruction with different weighting of low and high energies Application of Metal Artefact Reduction (MAR) software DECT MAR Kovacs et al R&O 2017
Improved precision AND accuracy Combination of MAR and DE CT most promising for H&N and pelvis, DE CT alone for spine Kovacs et al R&O 2017
Dual Energy CT Patients with metal implants (teeth, spine, hip) Qualitative (blind) evaluation : DECT-MAR images are most appropriate for delineation Kovacs et al R&O 2017
Removing motion artifacts: motion compensation Mercieca R&O 2017
Automatic delineation Atlas from consensus guidelines 20 OARs, nasopharyngeal carcinoma Improvement for some structure (superior pharyngeal constrictor muscle) but not others (parotids) Tao R&O 2015
Automatic delineation with machine learning? Kawata Physica Medica 2017
Conclusion Many approaches have proven efficient Education and guidelines are available for many treatment sites (target and OARs) Improvement in CT imaging / automated contouring solutions Novel imaging techniques are promising: costs/availability differ widely between approaches When performing a study, make sure the information is presented in terms of contour deviations, not just overlap