Tumor Control Probability (TCP) and Normal Tissue Complication Probability (NTCP) with Consideration of Cell Biological Effect

Abstract In radiotherapy, Tumor Control Probability (TCP) is a parameter used to calculate the percentage of tumor killing, while its effect on normal tissue damage describe by Normal Tissue Complication Probability (NTCP). Both TCP and NTCP depend on fractionation and cell biological effects such as repopulation, repair, redistribution and re-oxygenation. It also depends on the statistical distribution model used. One model that can review the biological effects of cells is the Poisson model. In this research, we modified the Poisson model by considering the four biological effects mentioned above on TCP and only the effect of repair on NTCP. The objective of this research is to investigate the most dominant effect that influences TCP value and the effect of repair on NTCP. The results show that the effect of repair and repopulation cause tumor cells cannot be erased completely while the effects of resenitization (re-oxygenation and redistribution) can facilitate tumor cells to die. It can be seen that the most dominant biological effect is the repair effect on the tumor. This effect can be minimized by reducing the length of dose delivery time. Furthermore, the repair effect on normal tissue can reduce the value of NTCP about 9% compared with other models. By using the ISO-NTCP curve we also get the spinal cord repair time after 15 hours.