Methods:  The dose volume constraint data for 12 organs at risk (OAR) corresponding to no grade ≥ 3 toxicity for SBRT, hypofractionated and convectional fractionation treatments were compiled from various sources such as TG101, QUANTEC and clinical trial database. These data cover 10 fractionation schemes. A linear-quadratic-linear (LQ-L) model was used to extract model parameters (e.g., $$\alpha/\beta$$,  $$\gamma/\alpha$$ and $$d_t$$) from fitting the Iso-BED curves of those dose volume constraints for the OARs using an in-house python code. The obtained model parameters were integrated into a practical workflow in MIM software. Their practicality was tested for treatment planning of re-irradiation.
Results:   The LQ-L model fitted the data well as indicated by smooth transition curves from SBRT to conventional fractionation data. The organ-specific model parameters were obtained, for example, $$\alpha/\beta$$=2.57Gy,  $$\gamma/\alpha$$=9.07Gy and $$d_t$$=7.65Gy, and $$\alpha/\beta$$=2.34Gy,  $$\gamma/\alpha$$=9.67Gy and $$d_t$$=6.80Gy for spinal cord and brainstem, respectively. The composite dose plans for retreatment of head and neck cancers with considering the obtained model parameters show up to 10% difference in physical dose constraints from traditional EQD2 method with $$\alpha/\beta$$=3.0Gy.