Room: Exhibit Hall
Purpose: A radiobiological model of reoxygenation and fractionation effects has been recently proposed. Based on this model, this work investigates the theoretical effect of reoxygenation in accelerated fractionation schemes for three tumour types.
Methods: Prostate cancer, glioblastoma and lung metastases have been selected to represent tumour cells with various radiobiological properties. The equivalent dose per fraction (EDF) is first calculated according to the linear-quadratic (LQ) model for the number of fractions less than the conventional fractionation schemes. EDF is then calculated using the newly proposed radiobiological model for reoxygenation. The portion of hypoxic cells becoming reoxygenated after each fraction Î” in the model is varied to observe its impact on EDF.
Results: In a single-fraction treatment for glioblastoma, the reoxygenation-corrected dose is found to be 22.4% and 39.0% higher than the LQ-predicted value assuming Î” = 0.1 and 0.3, respectively. For a 5-fraction treatment for prostate cancer, the differences are 23.0% and 33.4% assuming Î” = 0.1 and 0.3, respectively. For a 5-fraction treatment for glioblastoma and lung metastases with Î” = 0.1 (0.3), the differences are 28.2% (15.3%) and 1.4% (1.7%), respectively. The magnitude of the correction factors depend on the tumour type, radiotherapy schedule and Î”. Correction factors for some less extreme hypofractionated schemes are found to be less for Î” = 0.3 than for Î” = 0.1, while in the single-fraction treatments a larger correction factor is always associated with a larger value for Î”.
Conclusion: The required dose per fraction in an accelerated fractionation scheme according to the reoxygenation model is higher than what is obtained through the LQ model. The greatest difference is observed among the extreme hypofractionation schemes. Hypoxia in tumour during radiotherapy treatment should be further studied to verify the validity of the new model and to determine the optimal dose per fraction.