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Multimodality imaging with CT, MR and FDG-PET for radiotherapy target volume delineation in oropharyngeal squamous
David Bird1, Andrew F Scarsbrook2,3, Jonathan Sykes4
1Department of Radiotherapy Physics, St. James' University Hospital, Leeds Teaching Hospitals NHS Trust, Leeds, UK. david.bird3@nhs.net.
Background:
This study aimed to quantify the variation in oropharyngeal squamous cell carcinoma gross tumour volume (GTV) delineation between CT, MR and FDG PET-CT imaging.
Methods:
A prospective, single centre, pilot study was undertaken where 11 patients with locally advanced oropharyngeal cancers (2 tonsil, 9 base of tongue primaries) underwent pre-treatment, contrast enhanced, FDG PET-CT and MR imaging, all performed in a radiotherapy treatment mask. CT, MR and CT-MR GTVs were contoured by 5 clinicians (2 radiologists and 3 radiation oncologists). A semi-automated segmentation algorithm was used to contour PET GTVs. Volume and positional analyses were undertaken, accounting for inter-observer variation, using linear mixed effects models and contour comparison metrics respectively.
Results:
Significant differences in mean GTV volume were found between CT (11.9 cm(3)) and CT-MR (14.1 cm(3)), p < 0.006, CT-MR and PET (9.5 cm(3)), p < 0.0009, and MR (12.7 cm(3)) and PET, p < 0.016. Substantial differences in GTV position were found between all modalities with the exception of CT-MR and MR GTVs. A mean of 64 %, 74 % and 77 % of the PET GTVs were included within the CT, MR and CT-MR GTVs respectively. A mean of 57 % of the MR GTVs were included within the CT GTV; conversely a mean of 63 % of the CT GTVs were included within the MR GTV. CT inter-observer variability was found to be significantly higher in terms of position and/or volume than both MR and CT-MR (p < 0.05). Significant differences in GTV volume were found between GTV volumes delineated by radiologists (9.7 cm(3)) and oncologists (14.6 cm(3)) for all modalities (p = 0.001).
Conclusions:
The use of different imaging modalities produced significantly different GTVs, with no single imaging technique encompassing all potential GTV regions. The use of MR reduced inter-observer variability. These data suggest delineation based on multimodality imaging has the potential to improve accuracy of GTV definition.
Trial Registration:
ISRCTN Registry: ISRCTN34165059 . Registered 2nd February 2015.
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