An estimation of radiobiologic parameters from clinical outcomes for radiation treatment planning of brain tumor

Purpose: To estimate a plausible set of radiobiologic parameters such as α, α/β values, from clinical outcomes for biologically based radiation treatment planning of brain tumors. Methods and Materials: Linear-quadratic (LQ) formalism and the concept of equivalent uniform dose were used to analyze a series of published clinical data for malignant gliomas involving different forms of radiation therapy. Results: A plausible set of LQ parameters was obtained for gliomas: α = 0.06 ± 0.05 Gy-1, α/β = 10.0 ± 15.1 Gy, the tumor cell doubling time Td = 50 ± 30 days, with the repair half-time of 0.5 h. The present estimated biologic parameters can reasonably predict the effectiveness of most of the recently reported clinical results employing either single or combined radiation therapy modalities. Different LQ parameters between Grade 3 and Grade 4 astrocytomas were found, implying the radiosensitivity for different grade tumors may be different. Smaller α, β from in vivo was observed, indicating lower radiosensitivity occurred in vivo as compared with in vitro. Conclusions: A plausible set of radiobiologic parameters for gliomas was estimated based on clinical data. These parameters can reasonably predict most of the clinical results. They may be used to design new treatment fractionation schemes and to evaluate and optimize treatment plans