Variation in Radiotherapy Target Volume Definition, Dose to Organs at Risk and Clinical Target Volumes using Anatomic (Computed Tomography) versus Combined Anatomic and Molecular Imaging (Positron Emission Tomography/Computed Tomography): Intensity-modulated Radiotherapy Delivered using a Tomotherapy Hi Art Machine: Final Results of the VortigERN Study

Aims: Contrast-enhanced computed tomography (CECT) is the current standard for delineating tumours of the head and neck for radiotherapy. Although metabolic imaging with positron emission tomography (PET) has been used in recent years, the studies were non-confirmatory in establishing its routine role in radiotherapy planning in the modern era. This study explored the difference in gross tumour volume and clinical target volume definitions for the primary and nodal volumes when FDG PET/CT was used as compared with CECT in oropharyngeal cancer cases. Materials and methods: Twenty patients with oropharyngeal cancers had a PET/CT scan in the treatment position after consent. Target volumes were defined on CECT scans by a consultant clinical oncologist who was blind to the PET scans. After obtaining inputs from a radiologist, another set of target volumes were outlined on the PET/CT data set. The gross and clinical target volumes as defined on the two data sets were then analysed. The hypothesis of more accurate target delineation, preventing geographical miss and comparative overlap volumes between CECT and PET/CT, was explored. The study also analysed the volumes of intersection and analysed whether there was any TNM stage migration when PET/CT was used as compared with CECT for planning. Results: In 17 of 20 patients, the TNM stage was not altered when adding FDG PET information to CT. PET information prevented geographical miss in two patients and identified distant metastases in one case. PET/CT gross tumour volumes were smaller than CECT volumes (mean +/- standard deviation: 25.16 cm(3) +/- 35.8 versus 36.56 cm(3) +/- 44.14; P < 0.015) for the primary tumour. Interestingly, our study showed no significant differences in gross tumour volume for T1/T2 disease, although differences in gross tumour volumes for advanced disease (T3/T4) were significant. The nodal target volumes (mean +/- standard deviation: CECT versus PET/CT 32.48 cm(3) +/- 36.63 versus 32.21 cm(3) +/- 37.09; P > 0.86) were not statistically different. Similarity and discordance coefficients were calculated and are reported. Conclusion: PET/CT as compared with CECT could provide more clinically relevant information and prevent geographical miss when used for radiotherapy planning for advanced oropharyngeal tumours. Also, PET/CT provided a smaller better-defined target volume when compared with CECT. PET/CT-based volumes could therefore be used for treatment planning and targeted dose painting in oropharyngeal cancers. (C) 2012 Published by Elsevier Ltd on behalf of The Royal College of Radiologists.