Abstract
BackgroundThe accurate definition of organs at risk (OARs) is required to fully exploit the benefits of intensity-modulated radiotherapy (IMRT) for head and neck cancer. However, manual delineation is time-consuming and there is considerable inter-observer variability. This is pertinent as function-sparing and adaptive IMRT have increased the number and frequency of delineation of OARs. We evaluated accuracy and potential time-saving of Smart Probabilistic Image Contouring Engine (SPICE) automatic segmentation to define OARs for salivary-, swallowing- and cochlea-sparing IMRT.MethodsFive clinicians recorded the time to delineate five organs at risk (parotid glands, submandibular glands, larynx, pharyngeal constrictor muscles and cochleae) for each of 10 CT scans. SPICE was then used to define these structures. The acceptability of SPICE contours was initially determined by visual inspection and the total time to modify them recorded per scan. The Simultaneous Truth and Performance Level Estimation (STAPLE) algorithm created a reference standard from all clinician contours. Clinician, SPICE and modified contours were compared against STAPLE by the Dice similarity coefficient (DSC) and mean/maximum distance to agreement (DTA).ResultsFor all investigated structures, SPICE contours were less accurate than manual contours. However, for parotid/submandibular glands they were acceptable (median DSC: 0.79/0.80; mean, maximum DTA: 1.5 mm, 14.8 mm/0.6 mm, 5.7 mm). Modified SPICE contours were also less accurate than manual contours. The utilisation of SPICE did not result in time-saving/improve efficiency.ConclusionsImprovements in accuracy of automatic segmentation for head and neck OARs would be worthwhile and are required before its routine clinical implementation.
Highlights
The accurate definition of organs at risk (OARs) is required to fully exploit the benefits of intensity-modulated radiotherapy (IMRT) for head and neck cancer
The parotid-sparing intensity-modulated versus conventional radiotherapy in head and neck cancer (PARSPORT) trial demonstrated the incidence of grade ≥2 xerostomia one year after treatment was significantly reduced with parotid-sparing IMRT compared to 3Dconformal radiotherapy (38% versus 74%) [9]
The mean Dice similarity coefficient (DSC) were significantly reduced for Smart Probabilistic Image Contouring Engine (SPICE) contours compared with manual for all structures (Figure 2)
Summary
The accurate definition of organs at risk (OARs) is required to fully exploit the benefits of intensity-modulated radiotherapy (IMRT) for head and neck cancer. Manual delineation is time-consuming and there is considerable inter-observer variability. There is considerable inter-observer variability; [3,4,5,6] which can result in significant differences in radiation dose to OARs [4]. This has implications for: evaluation of radiotherapy plans; Following head and neck radiotherapy, adverse late effects are highly prevalent and these impact on both organ function and more general domains of well-being, such as physical, mental and social health [8]. Relatively modest reductions in dose (to less than 35Gy) may be of benefit [13]
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