Correlation between pretreatment FDG-PET biological target volume and anatomical location of failure after radiation therapy for head and neck cancers

Background and purposeTo assess whether the pretreatment FDG-PET-defined biologic target volume (PET-BTV) correlates with the anatomical sites of loco-regional failure (LRF) after RT for head and neck cancer (HNC).Materials and methodsWe retrospectively identified 61 HNC patients treated definitively with either 3-D CRT or IMRT who had a pre-therapy PET/CT. The GTV and high-risk CTV1 definitions included composite data obtained from diagnostic CT, PET/CT, physical examination, and MRI when available. The median CTV1 dose was 70 Gy. 95% received chemotherapy. For patients with LRF, a recurrence volume (Vr) was identified and was mapped to the pretreatment planning CT and pretreatment PET scan.ResultsAt a median follow-up of 22 months, 15% (9/61) patients had LRF. For patients with a LRF, 100% (9/9) of failures were inside the GTV. One of nine [11% (95% CI: 3–45%)] had Vr which mapped outside of the pretreatment PET-BTV, while 8/9 patients had Vr within the PET-BTV. Predictors of LRF in our series included GTV volume (p = 0.003), but not mean SUV (p = 0.13) or max SUV (p = 0.25).ConclusionsFollowing treatment in which the GTV was defined based on the composite of imaging and physical examination, the majority, but not all, LRF occurred within the PET-BTV. These results support an important, but not exclusive, role of FDG-PET in defining the GTV.