Multimodality imaging with CT, MR and FDG-PET for radiotherapy target volume delineation in oropharyngeal squamous cell carcinoma

Abstract

BackgroundThis study aimed to quantify the variation in oropharyngeal squamous cell carcinoma gross tumour volume (GTV) delineation between CT, MR and FDG PET-CT imaging.MethodsA 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.ResultsSignificant differences in mean GTV volume were found between CT (11.9 cm3) and CT-MR (14.1 cm3), p < 0.006, CT-MR and PET (9.5 cm3), p < 0.0009, and MR (12.7 cm3) 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 cm3) and oncologists (14.6 cm3) for all modalities (p = 0.001).ConclusionsThe 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 registrationISRCTN Registry: ISRCTN34165059. Registered 2nd February 2015.

Interobserver reliability of computed tomographic contouring of canine tonsils in radiation therapy treatment planning

“…Improving the repeatability and reliability of tumor delineation is critical in the era of highly conformal RT. In human oropharyngeal squamous cell carcinoma multimodality imaging with CT, MRI, and 18‐fluoride 2‐deoxyglucose/positron emission tomography for radiotherapy target volume delineation revealed that using the three imaging modalities produced significantly different gross tumor volumes which varied in volume and/or position . A recent study found no significant difference between average gross tumor volumes delineated using CT or MRI, whereas average gross tumor volumes utilizing positron emission tomography/CT were smaller.…”

“…Access to positron emission tomography scan facilities is limited in veterinary medicine. It has been reported that canine normal tonsils as well as inflammation or brown fat also uptake 18‐fluoride 2‐deoxyglucose which may affect the interpretation of tonsil loacalization …”

Evaluating diffusion‐weighted magnetic resonance imaging for target volume delineation in head and neck radiotherapy

“…The increase in GTV volume with additional imaging modalities compared to CT alone (13.37 cm 3 on average compared to 10.92 cm 3 for CT and 10.52 cm 3 for CT/PET) may be attributed to several factors such as how the observer interprets the images, the amount of experience the observer has and any delineation guidelines that may be in use . Furthermore, imaging modalities such as PET can have excellent contrast but low spatial resolution which can also impact GTV delineation . Having slightly larger GTV volumes with DWI may not be an issue as it is thought that current clinically used GTVs for primary HN tumours created by radiation oncologists may already be an overestimation of the actual GTV .…”

“…21 Furthermore, imaging modalities such as PET can have excellent contrast but low spatial resolution which can also impact GTV delineation. 23 Having slightly larger GTV volumes with DWI may not be an issue as it is thought that current clinically used GTVs for primary HN tumours created by radiation oncologists may already be an overestimation of the actual GTV. 2,24 On the other hand, it could be inferred that DWI adds uncertainty and therefore radiation oncologists contour larger volumes and this would increase the statistical likelihood of the volumes being incorrect.…”

Considerable interobserver variation in delineation of pancreatic cancer on 3DCT and 4DCT: a multi-institutional study

“…For the patients in our study, registration between the diagnostic CT and the planning CT was not performed because of a different position of the patient and a different anatomy as a result of the placement of the biliary stents and fiducial markers between both scans. Image registration between a diagnostic scan and planning CT scan may improve accuracy in target delineation and reduce interobserver variation as seen for other tumor sites [27–29]. …”