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Head and Neck Cancer Radiation Therapy
Atlas-based Auto-contouring –
Balancing Accuracy with Efficiency in OnQ rts ®
Susan Barley, 1 Clare Antoine, 2 Gareth Webster, 2 Marie Tiffany, 2 Navinah Nundlall, 2 Rosemary Simmons 3 and Andrew Hartley 4
1. Lead Clinical Scientist, Oncology Systems Limited, Shrewsbury, UK; 2. Medical Physicist; 3. Specialist Radiographer;
4. Clinical Oncologist, Queen Elizabeth Hospital, Birmingham, UK
Abstract Atlas-based auto segmentation with OnQ rts ® has been shown to deliver time-savings for the delineation of organs at risk in head and
neck patients being treated with intensity-modulated radiotherapy. However, as the initial time to set up atlases can be high in busy
departments the optimal number of atlas cases needed for auto-contouring was investigated. Using conformity index and mean distance
to conformity to compare automatically generated with gold standard clinical contours, it was found that the majority of contours were
unaffected by reducing the number of atlas cases from 30 to 10. The optimum number of atlas cases, however, was considered to be 20
due to the reduction in accuracy of the mandible, larynx and brain, below this level.
Keywords Radiation therapy, atlas-based segmentation, radiotherapy planning, deformable image registration, OnQ rts
Disclosures: Susan Barley is an employee of Oncology Systems Limited. Clare Antoine, Gareth Webster, Marie Tiffany, Navinah Nundlall, Rosemary Simmons and Andrew
Hartley have no conflicts of interest to declare.
Compliance with Ethical Guidelines: All procedures were followed in accordance with the responsible committee on human experimentation and with the Helsinki
Declaration of 1975 and subsequent revisions, and informed consent was received from the patients involved in this study.
Received: 13 October 2014 Accepted: 2 December 2014 Citation: European Oncology & Haematology, 2014;10(2):98–101
Correspondence: Susan Barley, Oncology Systems Limited (OSL), 14 Longbow Close, Shrewsbury, SY1 3GZ, UK. E: email@example.com
Support: The publication of this article was supported by Oncology Systems Limited.
Delineation of contours remains the one part of radiotherapy that
is completely manual in the majority of centres and therefore the
potential for time-saving is huge, 1 being estimated to range from
23 % 2 to 41 %. 3 One of the additional benefits of auto-contouring is the
reduction in inter-observer variation, which in general is not quantified
in radiotherapy. Balik et al., 4 showed that, when comparing the
demons and small deformation inverse consistent linear elastic (SICLE)
algorithm for propagating contours between cone beam computed
tomography (CBCT) scans of non-small cell lung carcinoma (NSCLC)
patients taken weekly, over 7 weeks that the Dice similarity coefficient
(DSC) for the two algorithms was similar to the DSC seen for manual
contouring between different trained observers. This shows that all
contours should be independently checked by a separate clinician. 3,5
However, if atlas-based contours are computer generated, the need for
the second clinician is replaced by one clinician checking the contours
produced by the software: 3 another potential manpower saving of an
create customised atlases, knowing what will work and how many
atlases are needed in the library is too much of a challenge to already
over-stretched centres, despite the time savings of a fully operational
system being well cited in the literature.
One cancer centre that has embraced the use of atlas-based segmentation
to outline the normal anatomy for all radical head and neck radiotherapy
treatment plans is Queen Elizabeth Hospital (QEB), Birmingham, UK.
Following on from research that showed that the use of OnQ rts (Oncology
Systems Limited, UK) (one of a number of commercially available software
products that can be used for atlas-based auto segmentation) could
reduce outlining time by 36 minutes – from 90 down to 54 minutes – work
has now been performed to establish the optimal number of atlases
required in the atlas library for the contouring of head and neck structures
and which structures are most affected by the number of atlases used.
This work will be reported in this paper.
Background Sharp et al. 6 performed an overview of the current status of auto
segmentation in clinical radiotherapy. One of the main findings of the
paper was that the atlases used should be customised and department
specific. The slow uptake in clinical use by centres that have purchased
commercially available software products that perform atlas-based
segmentation is in many cases linked to the need for atlases to
be customised and department specific. The initial input of time to
98 OnQ rts is a stand-alone software product that has been designed for
the display, evaluation, co-registration and fusion of medical images,
auto-contouring of anatomical structures and display of radiation
therapy dose distributions to aid in radiation therapy planning. The
auto-contouring protocol uses atlas-based segmentation of CT image
data and is available for the following anatomical sites: head and neck,
male pelvis, and thorax.
Eur op ean On c ol og y & Ha e matolog y