Is image registration of fluorodeoxyglucose-positron emission tomography/computed tomography for head-and-neck cancer treatment planning necessary?

To evaluate dosimetry and patterns of failure related to fluorodeoxyglucose-positron emission tomography (FDG-PET)-defined biological tumor volumes (BTVs) for head-and-neck squamous cell carcinoma (HNSCC) treated with definitive radiotherapy (RT).We conducted a retrospective study of 91 HNSCC patients who received pretreatment PET/CT scans that were not formally used for target delineation. The median follow-up was 34.5 months. Image registration was performed for PET, planning CT, and post-RT failure CT scans. Previously defined primary (CT(PRIMARY)) and nodal (CT(NODE)) gross tumor volumes (GTV) were used. The primary BTV (BTV(PRIMARY)) and nodal BTV (BTV(NODE)) were defined visually (PET(vis)). The BTV(PRIMARY) was also contoured using 40% and 50% peak PET activity (PET(40,) PET(50)). The recurrent GTVs were contoured on post-RT CT scans. Dosimetry was evaluated on the planning-CT and pretreatment PET scan. PET and CT dosimetric/volumetric data was compared for those with and without local-regional failure (LRF).In all, 29 of 91 (32%) patients experienced LRF: 10 local alone, 7 regional alone, and 12 local and regional. BTVs and CT volumes had less than complete overlap. BTVs were smaller than CT-defined targets. Dosimetric coverage was similar between failed and controlled groups as well as between BTVs and CT-defined volumes.PET and CT-defined tumor volumes received similar RT doses despite having less than complete overlap and the inaccuracies of image registration. LRF correlated with both CT and PET-defined volumes. The dosimetry for PET- and/or CT-based tumor volumes was not significantly inferior in patients with LRF. CT-based delineation alone may be sufficient for treatment planning in patients with HNSCC. Image registration of FDG-PET may not be necessary.