Fig. 3.

a Survival times for different chemotherapy doses in our model. Red point B depicts the maximum survival time; here, $T_s=120$ days correspond to $u=0.2192$. Points A and C are chosen to represent different behaviors of the tumor cells population for $u=0.1732$ ($T_s=80$ days) and $u=0.3704$ ($T_s=96$ days), respectively. b–d Evolution of the volumes of sensitive and resistant subpopulations, carrying capacity and total volume of the tumor for three different values of chemotherapy u corresponding to the points A, B, and C in a. The dotted lines mark the point at which the tumor volume reaches the critical level $N_{\mathrm{crit}}$. The initial condition is chosen as [280, 20, 650]