The main purpose of this study was to compare the location of initial hypermetabolic regions on baseline 18F-FDG PET scans with the metabolic relapse sites after radio-chemotherapy in Head and neck squamous cell carcinoma (HNSCC)

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.

Head and neck squamous cell carcinoma (HNSCC) is the eighth most common cancer worldwide with over half a million new cases diagnosed annually. Approximately two-thirds of HNSCCs are already advanced at diagnosis with a 5-year survival below 50%. The high mortality rate is largely due to recurrence occurring in the majority of the cases locally and within the first two years after curative treatment.

The initial functional tumor volume was significantly higher for patients with proven local recurrence or residual disease (23.5 cc vs. 8.9 cc; p = 0.0005). The overlap between baseline and follow-up sub-volumes was moderate with an overlap fraction ranging from 0.52 to 0.39 between R40 and I30 to I60.

Pre and post-treatment PET/CT scans of ninety-four HNSCC patients treated with radio-chemotherapy were retrospectively reviewed. Follow-up 18F-FDG PET/CT images were registered to baseline scans using a rigid body transformation.

Comparision

Seven metabolic tumor sub-volumes were obtained on the baseline scans using a fixed percentage of SUVmax (I30, I40, I50, I60, I70, I80, and I90) and were subsequently compared with two post-treatment sub-volumes (R40, R90) in 38 cases of local recurrence or residual metabolic disease. 

Overlap fraction, Dice and Jaccard indices, common volume/baseline volume and common volume/recurrent volume were used to determine the overlap of the differently estimated sub-volumes.

"In our study, the overlap between baseline and post-therapeutic metabolic tumor sub-volumes was only moderate. These results need to be investigated in a larger cohort acquired with a more standardized patient repositioning protocol for sequential PET imaging," said the researcher.