Fig. 1

Estimated tumour volume at time of therapy initiation (V_est) calculated using three different post-therapy tumour volume regression models versus true tumour volume at time of therapy initiation (V_i). The regression models were: Lin: Linear regression of the first two volume measurements after therapy, Exp: Exponential regression of the first two volume measurements after therapy, and EXP: Long-term exponential regression of tumour volume after therapy using all data until tumour volume reaches the minimum. Regression equations (intercept = 0): Lin: V = 0.91 Vi, (p < 0.00001); Exp: V = 2.30 Vi, (p < 0.01); EXP: V = 0.93 V_i, (non-significant). For the EXP model, the regression equation was V_est = 0.7 V_i, when an outlier point (V_est = 83.2, V_i = 5.7), which is not shown in this figure, was excluded and R² = 0.4 and was the correlation was still non-significant