The assessment of treatment response in glioblastoma is difficult with MRI because reactive blood-brain barrier alterations with contrast enhancement can mimic tumor progression. In this study, we investigated the predictive value of PET using O-(2-18 F-fluoroethyl)-L-tyrosine ( 18 F-FET PET) during treatment. Methods: In a prospective study, 25 patients with glioblastoma were investigated by MRI and 18 F-FET PET after surgery (MRI-/FET-1), early (7-10 d) after completion of radiochemotherapy with temozolomide (RCX) (MRI-/FET-2), and 6-8 wk later (MRI-/FET-3). Maximum and mean tumor-to-brain ratios (TBR max and TBR mean , respectively) were determined by region-of-interest analyses. Furthermore, gadolinium contrastenhancement volumes on MRI (Gd-volume) and tumor volumes in 18 F-FET PET images with a tumor-to-brain ratio greater than 1.6 (T vol 1.6 ) were calculated using threshold-based volume-ofinterest analyses. The patients were grouped into responders and nonresponders according to the changes of these parameters at different cutoffs, and the influence on progression-free survival and overall survival was tested using univariate and multivariate survival analyses and by receiver-operating-characteristic analyses. Results: Early after completion of RCX, a decrease of both TBR max and TBR mean was a highly significant and independent statistical predictor for progression-free survival and overall survival. Receiver-operating-characteristic analysis showed that a decrease of the TBR max between FET-1 and FET-2 of more than 20% predicted poor survival, with a sensitivity of 83% and a specificity of 67% (area under the curve, 0.75). Six to eight weeks later, the predictive value of TBR max and TBR mean was less significant, but an association between a decrease of T vol 1.6 and PFS was noted. In contrast, Gd-volume changes had no significant predictive value for survival. Conclusion: In contrast to Gd-volumes on MRI, changes in 18 F-FET PET may be a valuable parameter to assess treatment response in glioblastoma and to predict survival time.

SBRT for stage I NSCLC was safe and effective in this multi-institutional, academic environment, despite considerable interinstitutional variability and time trends in SBRT practice. Radiotherapy dose was identified as a major treatment factor influencing local tumor control and OS.

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