Respiratory-gated (4D) contrast-enhanced FDG PET-CT for radiotherapy planning of lower oesophageal carcinoma: feasibility and impact on planning target volume

BACKGROUND: To assess the feasibility and potential impact on target delineation of respiratory-gated (4D) contrast-enhanced (18)Fluorine fluorodeoxyglucose (FDG) positron emission tomography - computed tomography (PET-CT), in the treatment planning position, for a prospective cohort of patients with lower third oesophageal cancer. METHODS: Fifteen patients were recruited into the study. Imaging included 4D PET-CT, 3D PET-CT, endoscopic ultrasound and planning 4D CT. Target volume delineation was performed on 4D CT, 4D CT with co-registered 3D PET and 4D PET-CT. Planning target volumes (PTV) generated with 4D CT (PTV(4DCT),) 4D CT co-registered with 3D PET-CT (PTV(3DPET4DCT)) and 4D PET-CT (PTV(4DPETCT)) were compared with multiple positional metrics. RESULTS: Mean PTV(4DCT), PTV(3DPET4DCT) and PTV(4DPETCT) were 582.4 ± 275.1 cm(3), 472.5 ± 193.1 cm(3) and 480.6 ± 236.9 cm(3) respectively (no significant difference). Median DICE similarity coefficients comparing PTV(4DCT) with PTV(3DPET4DCT,) PTV(4DCT) with PTV(4DPETCT) and PTV(3DPET4DCT) with PTV(4DPETCT) were 0.85 (range 0.65–0.9), 0.85 (range 0.69–0.9) and 0.88 (range 0.79–0.9) respectively. The median sensitivity index for overlap comparing PTV(4DCT) with PTV(3DPET4DCT,) PTV(4DCT) with PTV(4DPETCT) and PTV(3DPET4DCT) with PTV(4DPETCT) were 0.78 (range 0.65–0.9), 0.79 (range 0.65–0.9) and 0.89 (range 0.68–0.94) respectively. CONCLUSIONS: Planning 4D PET-CT is feasible with careful patient selection. PTV generated using 4D CT, 3D PET-CT and 4D PET-CT were of similar volume, however, overlap analysis demonstrated that approximately 20% of PTV(3DPETCT) and PTV(4DPETCT) are not included in PTV(4DCT), leading to under-coverage of target volume and a potential geometric miss. Additionally, differences between PTV(3DPET4DCT) and PTV(4DPETCT) suggest a potential benefit for 4D PET-CT. TRIAL REGISTRATION: ClinicalTrials.gov Identifier – NCT02285660 (Registered 21/10/2014).