Identification of recurrence sites using initial PET/CT in head and neck cancer treated by radio-chemotherapy.

Objectives: Head and neck squamous cell carcinoma (HNSCC) treated by radio-chemotherapy have a significant local recurrence rate. It has been previously suggested that 18F-FDG PET could identify the high uptake areas that can be potential targets for dose boosting. The purpose of this study was to compare the location of the initial hypermetabolic lesions and with the location of the relapses after radio-chemotherapy in HNSCC.

Methods: 40 HNSCC patients treated with radio-chemotherapy were retrospectively included in this analysis. A rigid registration was performed on both baseline and follow-up 18F-FDG PET-CT. Seven metabolic tumor sub-volumes were obtained on the baseline scans using a fixed percentage threshold of SUVmax (I30, I40, I50, I60, I70, I80, and I90) and were subsequently compared with two post-treatment sub-volumes (R40, R90) in cases of local recurrence or residual disease. Overlap fraction, Dice and Jaccard indices, common volume/baseline volume and common volume/recurrent volume were used to estimate the overlap of the different estimated sub-volumes.

Results: The initial tumor volume was significantly higher for 18 patients with proven local recurrence or residual disease (21.2cc vs. 11.2cc; p=0 .0005). The overlap between baseline and follow-up sub-volumes were moderate with an overlap fraction range from 0.25 to 0.4 for R40 and I30 to I60.

Conclusion: In our study the overlap between baseline and post therapeutic metabolic tumor sub-volumes was moderate. These preliminary results need to be investigated in a larger cohort with a more standardized repositioning method. Research Support: none