SUV max as measured by 18F-FDG PET in the second week of radiotherapy predicted two-year survival, according to a study published in the October issue of The Journal of Nuclear Medicine. Previous studies have hinted at the prognostic value of 18F-FDG PET uptake in patients with non-small cell lung cancer. These data are critical as response assessment early in the radiotherapy treatment could help tailor treatments to individual patients.
Wouter van Elmpt, MD, from the department of radiation oncology at Maastricht University Medical Center in the Netherlands, and colleagues hypothesized that early changes in FDG uptake could predict treatment success.
The researchers enrolled 34 consecutive lung cancer patients scheduled for radical radiotherapy from July 2008 to December 2008. They performed 18F-FDG PET/CT prior to therapy and in the second week of radiotherapy and completed a quantitative analysis of 18F-FDG uptake using SUV. Two-year overall survival served as the endpoint.
“The maximum SUV and mean SUV inside the PET volume for the entire population was 10.0 +/- 4.9 and 6.6 +/-3.2, respectively, for the pretreatment scan, compared with 8.8 +/- 4.2 and 5.9 +/- 2.9, respectively for the mid-treatment scan,” wrote van Elmpt et al.
The researchers observed significant differences in mean SUV among patients who survived for two years compared with those who did not. The average change in mean SUV inside the PET volume was -20.2 percent +/- 20.5 percent for patients who survived for two years. The corresponding range for those who did not survive was +2.1 percent +/- 21.9 percent.
van Elmpt and colleagues used the European Organization for Research and Treatment of Cancer (EORTC) threshold of 15 percent for partial metabolic response to divide the cohort into two groups. A total of 92 percent of patients with an SUV decrease of more than 15 percent survived for two years. In contrast, 33 percent of patients with a mean SUV decrease less than 15 percent survived for two years. Thus, the current study confirmed the EORTC criteria correlate with two-year survival.
“This is one of the first studies showing that repeated 18F-FDG PET early during radiotherapy has added value by being a predictive factor for survival before CT changes become evident. …The simplicity of calculating the average 18F-FDG uptake inside the primary tumor is one of the factors that could be exploited in clinical practice for individualizing treatment,” the researchers wrote.
van Elmpt et al called for future larger studies, which might uncover additional prognostic or predictive factors that incorporate stage or histologic types.
They also explained how the PET data might be applied in practice. For responders, therapy could continue as planned, and a new treatment plan might be developed for nonresponders. However, they cautioned that a clinical trial is required before this strategy could be deployed in practice.