Fig. 4

Best achievable root-mean-squared error (RMSE) values as a function of the latest used measurement time t_last for different fractions of systematic error f_syst of a 25%, b 50% and c 75%. The RMSE of the kidneys (filled black) and the tumours (open grey) for different number of time points TPs (2: square; 3: circle; 4: star) are depicted. The horizontal lines represent RMSE = 10 % (black dashed) and RMSE = 15% (grey dashed) representing the ad hoc assumed limits for the kidneys and tumours, respectively