Purpose

Early assessment of tumour response to treatment with repeated FDG-PET-CT imaging has potential for treatment adaptation but it is unclear what the optimal time window for this evaluation is. Previous studies indicate that changes in SUVmean and the effective radiosensitivity (αeff, accounting for uptake variations and accumulated dose until the second FDG-PET-CT scan) are predictive of 2-year overall survival (OS) when imaging is performed before radiotherapy and during the second week. This study aims to investigate if multiple FDG-PET-derived quantities determined during the third treatment week have stronger predictive power.

Methods

Twenty-eight lung cancer patients were imaged with FDG-PET-CT before radiotherapy (PET1) and during the third week (PET2). SUVmean, SUVmax, SUVpeak, MTV41%–50% (Metabolic Tumour Volume), TLG41%–50% (Total Lesion Glycolysis) in PET1 and PET2 and their change (), as well as average αeff (α¯eff) and the negative fraction of αeff values (fαeff<0) were determined. Correlations were sought between FDG-PET-derived quantities and OS with ROC analysis.

Results

Neither SUVmean, SUVmax, SUVpeak in PET1 and PET2 (AUC = 0.5–0.6), nor their changes (AUC = 0.5–0.6) were significant for outcome prediction purposes. Lack of correlation with OS was also found for α¯eff (AUC = 0.5) and fαeff<0 (AUC = 0.5). Threshold-based quantities (MTV41%–50%, TLG41%–50%) and their changes had AUC = 0.5–0.7.

P-values were in all cases ≫0.05.

Conclusions

The poor OS predictive power of the quantities determined from repeated FDG-PET-CT images indicates that the third week of treatment might not be suitable for treatment response assessment. Comparatively, the second week during the treatment appears to be a better time window.