Automated biological target volume delineation for radiotherapy treatment planning using FDG-PET/CT

Background: This study compared manually delineated gross tumour
volume (GTV) and automatically generated biological tumour volume
(BTV) based on fluoro-deoxy-glucose (FDG) positron emission
tomography (PET)/CT to assess the robustness of predefined PET
algorithms for radiotherapy (RT) planning in routine clinical
practice. Methods: RT-planning data from 20 consecutive patients
(lung-(40\%), oesophageal-(25\%), gynaecological-(25\%) and
colorectal (10\%) cancer) who had undergone FDG-PET/CT planning
between 08/2010 and 09/2011 were retrospectively analysed, five of
them underwent neoadjuvant chemotherapy before radiotherapy. In
addition to manual GTV contouring, automated segmentation
algorithms were applied-among these 38\%, 42\%, 47\% and 50\%
SUVmax as well as the PERCIST total lesion glycolysis (TLG)
algorithm. Different ratios were calculated to assess the overlap
of GTV and BTV including the conformity index and the ratio GTV
included within the BTV. Results: Median age of the patients was 66
years and median tumour SUVmax 9.2. Median size of the GTVs defined
by the radiation oncologist was 43.7 ml. Median conformity indices
were between 30.0-37.8\%. The highest amount of BTV within GTV was
seen with the 38\% SUVmax algorithm (49.0\%), the lowest with 50\%
SUVmax (36.0\%). Best agreement was obtained for oesophageal cancer
patients with a conformity index of 56.4\% and BTV within GTV ratio
of 71.1\%. Conclusions: At present there is only low concordance
between manually derived GTVs and automatically segmented
FDG-PET/CT based BTVs indicating the need for further research in
order to achieve higher volumetric conformity and therefore to get
access to the full potential of FDG-PET/CT for optimization of
radiotherapy planning.