Tumor-to-muscle ratio of Cu-ATSM uptake may reflect outcome of treatment in head-and-neck cancers

Objectives Tracer distributions of [F-18]fluorodeoxyglucose (FDG) and [Cu-62]diacetyl-bis(N4-methlythiosemicarbazone) (Cu-ATSM), a hypoxic tissue imaging tracer, were compared in head-and neck cancers, and evaluated the predictability of effectiveness of tumor treatment.

Methods Twenty-seven patients with head-and-neck cancer (mean age: 65 ± 14 y.o.) underwent Cu-ATSM-PET and FDG-PET/CT within a week interval. For Cu-ATSM PET images, 10 to 20 min data after 600-800 MBq tracer injection were used for analysis. After co-registration of Cu-ATSM-PET and FDG-PET/CT images, region of interest (ROI) was placed on the tumour mass using the threshold of 40% of maximum value for each PET image to obtain standardized uptake values (SUV) of each tumour. Maximum SUV (SUVmax) for each tracer and progression-free survival (PFS) period after treatment were compared. SUV values of muscles in the head-and-neck region were also obtained and tumour-to-muscle (T/M) ratio was calculated. Relationships between PET parameters and PFS period were analyzed to assess which was the most appropriate parameter to predict prognosis of head-and neck cancers.

Results Twenty-two patients had squamous cell carcinoma and 5 had adenocarcinoma. Twenty-two of them received chemoradiation therapy and 5 underwent surgical treatment. They were followed up by US, CT or FDG-PET/CT and the end-point of the follow-up for PFS was set at the time of recurrence or metastasis of the cancer. Sixteen of the patient showed recurrence or metastasis and the mean PFS period was 6.5 ± 6.8 months. In the PET parameters of SUVmax and T/M ratio, only T/M ratio of Cu-ATSM showed correlation with the PFS when using the mean value as a cutoff (Kaplan-Meier Logrank analysis).

Conclusions In patients with head-and-neck cancer, degree of Cu-ATSM accumulation may predict the poor prognosis after treatment when using the T/M ratio. SUVmax values as well as FDG-T/M ratio did not show correlation with PFS after the cancer therapy.