We used 3-deoxy-3-18 F-fluorothymidine (FLT) PET-CT to delineate biological tumour volume in thoracic oesophageal carcinoma, for a treatment planning simulation. We compared results with that of 18 F-fluorodeoxyglucose (FDG) PET-CT, on the basis of dosimetric analysis. Methods: 22 patients with oesophageal squamous-cell carcinoma detected by FLT and FDG PET-CT were enrolled. We used the treatment planning system to compare hypothetical treatment plans based on the optimal threshold for standard

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... uptake value of FLT and FDG PET-CT. We compared parameters in dosevolume histograms of the two groups, planning fields in similar directions and ensuring the prescribed dose line surrounded 95% of the target volume. Findings: Gross tumour volume, clinical target volume, and planning target volume were less with FLT than with FDG PET-CT imaging. The conformity index and homogeneity index did not differ significantly between FLT and FDG PET-CT treatment planning. The difference in V 20 of bilateral lung, V 40 of heart, and maximum dose received by the spinal cord did not differ significantly between FLT and FDG. Values for mean lung dose, V 5 , V 10 , V 30 , V 40 , and V 50 of bilateral lung, and mean heart dose and V 30 of heart were significantly lower with FLT PET-CT based planning than with FDG PET-CT (t = -5.442 to À2.637, p < 0.05). Interpretation: Treatment planning based on FLT PET-CT had potential benefits for some organs at risk, such as lungs and heart.