Effects of the cell cycle on the tumor control probability (TCP) in radiation treatment and comparison of treatment protocols

An important quantity to predict treatment success is the Thmor Control Probability (TCP). Current TCP models assume homogeneous tumor populations. It is known, however, that during the cell cycle, radiosensitivity is different for cancerogenic cells. Recently, a TCP formalism has been developed taking the cell cycle effect into account by Dawson and Hillen (DH). We analyze this TCP and compare to the commonly used TCP by Zaider-Minerbo (ZM), which ignores the cell cycle. It is possible to reduce the DH model to the ZM model. If the cell cycle is slow and there exists a significant resting phase, then the cell cycle effect cannot be neglected. Sensitivity analysis on the TCP by DH shows that the parameters related to the resting phase have a major effect on the TCP. Synchronizing cells initially can increase the TCP. We also compare several fractionation protocols applied in the treatment of prostate cancer, and see for example that applying radiation once-per-day might be better than applying half twice-a-day.