Jenny Hoang
The study was performed because we saw that clinicians were turning toward PET to provide information on early treatment or “intratreatment” response in head and neck squamous cell cancer (HNSCC). They saw an opportunity for intratreatment PET to detect favorable or unfavorable metabolic changes early in treatment and help to determine whether a particular therapeutic strategy should be maintained or changed.
However, a factor limiting interpretation of intratreatment PET is the intrinsic variability of standard uptake value (SUV) in the absence of treatment. This variability in SUV reflects biologic, technical, and observer variation, and it would be a major pitfall to misinterpret baseline fluctuation in SUV as early tumor response or tumor resistance to chemoradiation. Thus, the quantification of both baseline variability and intratreatment change is necessary in order to incorporate intratreatment PET imaging into adaptive therapy strategies for HNSCC.
We performed a prospective study to define the intrinsic (pretreatment) variability of tumor SUV and compared it with early treatment-induced (intratreatment) change in patients with HNSCC. We quantified repeatability for baseline studies and percentage change in SUV on the intratreatment PET. The main finding was that the repeatability coefficient (RC) derived for nodal metastatic disease was 10%, which implied that intratreatment change in SUV would have to be greater than 10% to be confident that the change represented more than baseline variability. In our study the only patient with intratreatment change in SUV above the RC was 1 of 2 patients with residual disease after chemoradiation.