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Proceedings Paper

Impact of region contouring variability on image-based focal therapy evaluation
Author(s): Eli Gibson; Ian A. Donaldson; Taimur T. Shah; Yipeng Hu; Hashim U. Ahmed; Dean C. Barratt
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Paper Abstract

Motivation: Focal therapy is an emerging low-morbidity treatment option for low-intermediate risk prostate cancer; however, challenges remain in accurately delivering treatment to specified targets and determining treatment success. Registered multi-parametric magnetic resonance imaging (MPMRI) acquired before and after treatment can support focal therapy evaluation and optimization; however, contouring variability, when defining the prostate, the clinical target volume (CTV) and the ablation region in images, reduces the precision of quantitative image-based focal therapy evaluation metrics. To inform the interpretation and clarify the limitations of such metrics, we investigated inter-observer contouring variability and its impact on four metrics.

Methods: Pre-therapy and 2-week-post-therapy standard-of-care MPMRI were acquired from 5 focal cryotherapy patients. Two clinicians independently contoured, on each slice, the prostate (pre- and post-treatment) and the dominant index lesion CTV (pre-treatment) in the T2-weighted MRI, and the ablated region (post-treatment) in the dynamic-contrast- enhanced MRI. For each combination of clinician contours, post-treatment images were registered to pre-treatment images using a 3D biomechanical-model-based registration of prostate surfaces, and four metrics were computed: the proportion of the target tissue region that was ablated and the target:ablated region volume ratio for each of two targets (the CTV and an expanded planning target volume). Variance components analysis was used to measure the contribution of each type of contour to the variance in the therapy evaluation metrics.

Conclusions: 14–23% of evaluation metric variance was attributable to contouring variability (including 6–12% from ablation region contouring); reducing this variability could improve the precision of focal therapy evaluation metrics.

Paper Details

Date Published: 18 March 2016
PDF: 6 pages
Proc. SPIE 9786, Medical Imaging 2016: Image-Guided Procedures, Robotic Interventions, and Modeling, 97861K (18 March 2016); doi: 10.1117/12.2216654
Show Author Affiliations
Eli Gibson, Univ. College London (United Kingdom)
Radboud Univ. Medical Ctr. (Netherlands)
Ian A. Donaldson, Univ. College London (United Kingdom)
Taimur T. Shah, Univ. College London (United Kingdom)
Yipeng Hu, Univ. College London (United Kingdom)
Hashim U. Ahmed, Univ. College London (United Kingdom)
Dean C. Barratt, Univ. College London (United Kingdom)

Published in SPIE Proceedings Vol. 9786:
Medical Imaging 2016: Image-Guided Procedures, Robotic Interventions, and Modeling
Robert J. Webster; Ziv R. Yaniv, Editor(s)

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