Radiotherapy is a common method for cancer treatment. One of the factors that determine the tumor’s malignancy is the presence of cancer stem cells in tumors. These cells not only have a long lifespan but also are capable to proliferate infinitely and have inherent resistance against all therapy methods. The aim of this research is to consider biological processes and their effects on each other in growth and radiotherapy phases by modeling to make the simulation closer to reality. Two main cell’s nutrients, including oxygen and glucose, biological tumor structure, cell cycle phases and telomere length limitation for the mitotic division are considered in the growth phase. Furthermore, 5R factors, cell’s different radiosensitivity in different oxygen levels, and cell’s different radiosensitivity in different cell cycle phases not being allowed to pass checkpoints in cell cycle until the complete repair of sublethal damage caused by radiotherapy, considered in the treatment phase. Then, three radiotherapy patterns were simulated for a heterogeneous tumor having three subpopulations: healthy cells, cancer cells, cancer stem cells. Obtained results are in agreement with the researches in this field.

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