Usefulness of the total lesion glycolysis (TLG) ratio in predicting the therapeutic effect of head and neck cancer-A novel parameter-

Objectives In predicting therapeutic effect of head and neck cancer using FDG-PET/CT, both metabolic tumor volume (MTV) and total lesion glycolysis (TLG) are useful parameters. However, threshold of the measurement is various such as SUV2.5 (fixed value) or 40% of SUVmax. Moreover, these parameters do not reflect deviation of the glucose metabolism distribution. We might be able to estimate the cancer’s invasiveness and also therapeutic effect by calculating tumor glucose metabolism distribution such as the ratio of higher TLG lesion. In the current study, we developed novel parameter (TLG ratio) and evaluated the usefulness for predicting the effect of head and neck cancer treatment.

Methods We analyzed 31 head and neck cancer treated by chemotherapy or chemo-radio therapy retrospectively (hypopharyngeal cancer 8, gingival cancer 6, tongue cancer 6, laryngeal cancer 5, maxillary cancer 3, oropharyngeal cancer 3). FDG-PET/CT examinations were done at a week before the start of cancer therapy and at three months after the cancer therapy. According to PERCIST criteria, we divided all patients into two groups (Responders: CMR or PMR 19, Non-responders: SMD or PMD 12). We calculated two kinds of TLG by setting the lower threshold using SUV2.5 (named as TLG2.5) and lower threshold using the 70 % of SUVmax (named as TLG70%). TLG2.5 reflects glucose metabolism of the whole tumor, and TLG70% reflects a higher glucose metabolism lesion. Then we calculated TLG ratio by the formula TLG70%/TLG2.5 (named as TLG70%/2.5), which indicates the distribution of the higher metabolic lesion. We compared the FDG parameters of pre-therapy examination (SUVmax, SUVpeak, TLG2.5, TLG70% and TLG70%/TLG2.5) between the two groups. And we compared the accuracy of therapeutic effect among all FDG parameters under condition of the optimal cut-off level.

Results In the pre-therapy FDG-PET/CT, values of TLG70%, TLG2.5 and TLG70%/2.5 were significantly higher in responders group compared to those of non-responders group (Table). The predictive capability of cancer therapy was significantly higher in TLG70% and TLG70%/2.5. Although not statistically significant, TLG70%/2.5 had better diagnostic capability than TLG70% (Figure).

Conclusions Higher TLG value before the treatment was confirmed to be predictive factor for poor prognosis in head and neck cancer. In addition, TLG70%/TLG2.5 which is a ratio of high glucose metabolism lesion will be useful as an additional parameter in predicting the effect of therapy of head and neck cancer before the treatment. $$graphic_14077916-8F90-4E7B-BCE2-E22B42F6A468$$