DNA double strand breaks (DSBs) pose serious threat to life. Efficient repair of DSBs is crucial for maintaining genomic integrity. Dynamic investigations of DSB repair have received intensive attention. However

previous models do not take into account the relation between extrinsic and intrinsic DNA damage. Therefore

a refined Monte Carlo model was constructed by considering spontaneous DNA damage and setting a threshold for cell cycle reentry. The refined model can better describe the dynamic DSB repair under stressed conditions. Extrinsic DSBs induced by irradiation were first fixed. When the level of damage falls below the threshold

intrinsic DNA damage will then emerge and both the extrinsic and intrinsic DSBs will possibly be simultaneously repaired during a specific period. The current model integrates both extrinsic and intrinsic DNA damage and sets a fertile ground for other models with DNA damage repair process.