Author: Makunda Aryal, Qiongge Li, Sook Kien Ng, Christopher F. Njeh, Edwin Quashie, Senthamizhchelvan Srinivasan, Yun Wang 👨🔬
Affiliation: Indiana University Medical School, Memorial Health Care System, Indiana University, Inova Hospital, Indiana University School of Medicine, Department of Radiation Oncology 🌍
Purpose: Linear-Quadratic-Linear (LQL) model is a modification of the traditional Linear-Quadratic model used in radiobiology to describe cell survival in response to radiation. The LQL model extends the LQA model to better account for cell survival at high fractional doses, where the LQ model is known to underestimate survival at higher fractional doses. While Equivalent dose in 2-Gy fractions (EQD2) based on biological effective dose (BED -LQ) is well documented, a formalism of EQD2 based on (BED-LQL) has not been established. This work is to introduce such a formulation of EQD2-LQL.
Methods: The EQD2-LQL formalism was derived by rearranging of the BED-LQL equation to isolate the total physical dose. The total physical dose is further simplified to account for the two distinct regains of the LQL model. Modeling parameters obtained from the BED-LQL model were used to calculate EQD2-LQL values for a standard fractionation of 30 x 200 cGy/fraction, with α/β values ranging from 2 to11 Gy.
Results: The EQD2-LQL equation was validated by comparing its results with EQD2-LQ for different α/β values across various fractionation schemes equivalent to 30 x 200cGy/fraction in BED. A 2% difference was observed in spinal cord, brainstem and esophagus. No differences were found for optic pathway and brachial plexus.
Conclusion: EQD2-LQL formalism provides novel approach to more accurately calculate homogenous physical dose distribution for high fractional dose as LQL model is more applicable in such situations.