Lung stereotactic ablative body radiotherapy: A large scale multi-institutional planning comparison for interpreting results of multi-institutional studies

• To compare from dosimetric and equivalent doses point of view, SABR plans of lung cancer patients from 26 centers.
• To compare plans with various TPS’s, delivery technologies and dose normalization approaches.
• To analyze the gEUD2, MLD2 and constraints fulfillment against planner expertise and involved technology.

PurposeA large-scale multi-institutional planning comparison on lung cancer SABR is presented with the aim of investigating possible criticism in carrying out retrospective multicentre data analysis from a dosimetric perspective.MethodsFive CT series were sent to the participants. The dose prescription to PTV was 54 Gy in 3 fractions of 18 Gy. The plans were compared in terms of PTV-gEUD2 (generalized Equivalent Uniform Dose equivalent to 2 Gy), mean dose to PTV, Homogeneity Index (PTV-HI), Conformity Index (PTV-CI) and Gradient Index (PTV-GI). We calculated the maximum dose for each OAR (organ at risk) considered as well as the MLD2 (mean lung dose equivalent to 2 Gy). The data were stratified according to expertise and technology.ResultsTwenty-six centers equipped with Linacs, 3DCRT (4% – 1 center), static IMRT (8% – 2 centers), VMAT (76% – 20 centers), CyberKnife (4% – 1 center), and Tomotherapy (8% – 2 centers) collaborated. Significant PTV-gEUD2 differences were observed (range: 105–161 Gy); mean-PTV dose, PTV-HI, PTV-CI, and PTV-GI were, respectively, 56.8 ± 3.4 Gy, 14.2 ± 10.1%, 0.70 ± 0.15, and 4.9 ± 1.9. Significant correlations for PTV-gEUD2 versus PTV-HI, and MLD2 versus PTV-GI, were observed.ConclusionsThe differences in terms of PTV-gEUD2 may suggest the inclusion of PTV-gEUD2 calculation for retrospective data inter-comparison.