  Background: Radiotherapy outcomes are usually predicted using the Linear
Quadratic model. However, this model does not integrate complex features of
tumor growth, in particular cell cycle regulation.
  Methods: In this paper, we propose a multiscale model of cancer growth based
on the genetic and molecular features of the evolution of colorectal cancer.
The model includes key genes, cellular kinetics, tissue dynamics, macroscopic
tumor evolution and radiosensitivity dependence on the cell cycle phase. We
investigate the role of gene-dependent cell cycle regulation in the response of
tumors to therapeutic irradiation protocols.
  Results: Simulation results emphasize the importance of tumor tissue features
and the need to consider regulating factors such as hypoxia, as well as tumor
geometry and tissue dynamics, in predicting and improving radiotherapeutic
efficacy.
  Conclusion: This model provides insight into the coupling of complex
biological processes, which leads to a better understanding of oncogenesis.
This will hopefully lead to improved irradiation therapy.
