dr. farzad khalvati – chief technology officer [email protected] march 2012 overcoming...

Dr. Farzad Khalvati – Chief Technology [email protected]

March 2012 www.segasist.com

Overcoming Variability in Medical Image Contouring

SegasistTM

mailto:[email protected]

Contouring

Any medical image (CT/MRI/US/PET etc.)

Region of interest (ROI), e.g. tumour

Contouring by clinician (radiologist, oncologist, pathologist etc.)

Copyright © Segasist Technologies 2008-11

ebo-enterprises.com

Contouring is necessary

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• Cancer treatment needs contouring

• Cancer occurs frequently; e.g. Prostate cancer: • The most common non-skin cancer for

adult males• The third leading cause of cancer death

for men in Canada with incidence rates on the rise

• One in six men in Canada will be afflicted by prostate cancer during their lifetimes.

• Contouring is an important part of diagnosis, monitoring, and treatment


Software A Software B Software C Software D Software E

Many modalities/cases: 664 Billion images/year in the US alone

Prostate MR Breast U/S Brain CT Prostate U/S Lung X-Ray

Extracted lesion/tissue/organ used for diagnosis/treatment planning/intervention

Contouring: The Challenge of Segmentation

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Small Problem:

- 5 -Copyright © Segasist Technologies 2008-11

Small Problem: Contouring takes time


Demand Snapshot: Radiation Oncology

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2010-2020: The number of cancer patients will increase by 22%, while the number of radiation oncologists will increase by just 2%. Study published in The Journal of Clinical Oncology, October 18, 2010

Contouring is a major bottleneck (0.25-3 hours/patient)

7

Volume Contouring Dose Calculation Treatment

Bigger Problem: Experts contour differently


Contouring is qualitative….

First expert

Second expert

First expert

Second expert

Inter-Observer Variability

Biggest Problem: Same expert contours differently


Contouring is qualitative….

First expert

First expert contours again

First expert

First expert contours again

Intra-Observer Variability

Inter- and Intra-Observer Variability

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"The failure by the observer to measure or identify a phenomenon accurately, which results in an error. Sources for this may be due to the observer's missing an abnormality, or to faulty technique resulting in incorrect test measurement, or to misinterpretation of the data."

Source: National Library of Medicine

Inherent anatomical vagueness/ambiguity Limitations of imaging devices Level of expertise of the expert (Partial) Subjectivity


The Curse of Variability: Solution

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• There is no Perfect segmentation algorithm

• Consensus Contour: for a given organ/tumour, consensus contour of multiple contours is the one that agrees with all of them the most

• Different algorithms can be used: STAPLE

• The result contour has maximum sensitivity and specificity with all input contours


The Curse of Variability: Examples

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Soft-tissue sarcoma: 13% [Roberge et al., Cancer/Radiothérapie 2011]

Prostate: 18% [White et al., Clinical Oncology 2009]

Bladder: 32% [Foroudi et al., Med. Imaging & Rad. Onc., 2009]

Abdominal aorta: 40% [England et al., Radiography 2008]

Breast lumpectomy cavity: 45% [Dzhugashvili et al., Rad.Onc. 2009]

Pulmonary nodules: 54% [Bogot et al., Academic Radiology 2005]

…

Conventional Consensus Building


It requires experts actually contour the same image

Not feasible: Too costly to afford!

Semi-Conventional Consensus Building


• Instead of experts actually contour the same image;

• Use previously created Atlases of the experts to generate contours

• Use the Atlas-based generated contours to build consensus

Conventional Atlas-Based Segmentation

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Atlas New Image

Best Match Registration


Consensus Building


Average Weighted average Distance optimization STAPLE algorithm

Segasist Reconcillio


Variability captured

One user

Consistency verification

intra-observer variability

All users

Consensus building

inter-observer variability

Segasist Reconcillio


ComputationalConsensus

Segasist Technologies


• University of Waterloo Spin-off

• Founded in 2008

• Toronto-based

• Products:• Prostate Auto-Contouring: FDA cleared• Segasist Auto-Contouring• Segasist Reconcillio

Thank You

Questions?

Dr. Farzad Khalvati, Ph.D. – Chief Technology Officer

[email protected]

www.segasist.com

SegasistTM

mailto:[email protected]

dr. farzad khalvati – chief technology officer [email protected] march 2012 overcoming...

Documents

contouring cancer

expert contours

tumour contouring

cancer treatment

prostate cancer

curse of variability

number of cancer patients

small problem