Room: ePoster Forums
Purpose: To determine the optimal irradiation interval of fractionated stereotactic radiosurgery (SRS) by an improved cellular automata (CA) model.
Methods: The tumor growth process was simulated by considering the amount of oxygen and the density of blood vessels, which supply oxygen and nutrient required for cell growth. Cancer cells died by the mitotic death process due to radiation, which was quantified by the LQ-model, or the apoptosis due to the lack of nutrient. The radiation caused increased oxygen permeation through the blood vessel or the breakdown of the vasculature resulting in a decrease of oxygen and nutrient. Consequently, these changes lead to a change in the tumor growth rate after irradiation. The optimal model parameters were determined by matching the simulation results with experimental data of the mice tumor volume for various doses. We did 1000 simulations per case. The Î±/Î² value of the LQ model was set to 5. The tumor control probability (TCP) was defined as the ratio of the number of histories in which all cancer cells died after the irradiation to the total number of the histories per simulation. The optimal irradiation interval was defined as the irradiation interval that TCP was the maximum.
Results: The model parameters, which reproduced the experimental curves of the mice tumor volume, were 0.6 days, 6 days, and 10 days for the tumor doubling time, the clearance time of dead cells, and the half-life of apoptotic cell death, respectively. The optimal irradiation interval for two-fraction SRS (13.5 Gy x 2) was 6 day.
Conclusion: The new model could fit the mice experimental data very well. The amount of nutrient and the oxygen available for cancer cells strongly influenced tumor proliferation, consequently TCP. Furthermore, we showed that the improved CA model could be used to optimize the irradiation interval.