Synergic effects between the photosensitizer concentration, C, and light fluence, F, on the model parameters.

<p>The three model parameters (<i>T, r, k</i>) were analyzed with respect to C.F values. A) Any reduction of the time constant <i>T</i> suggests a faster decrease of the transient phase (positive therapeutic effect). Almost all the values of <i>T</i> below a reference threshold fixed to <i>log(T) = 0</i> correspond to a synergistic condition defined by C.F ≥5. B) Any reduction of the transformed cell index (TCI) growth rate <i>r</i> suggests a slow down of the steady-state growth rate during its post-transient phase (positive therapeutic effect). Conversely, any increase of it leads to locally degrading the therapeutic response. Almost all the values of <i>r</i> below a reference threshold fixed to <i>r = 0 (no steady-state growth)</i> correspond to a synergistic condition defined by C.F ≥5. C) Any positive enhancement of the magnitude of the transient decrease <i>k</i> suggests a deeper decrease of the TCI during its transient decrease (positive therapeutic effect). Conversely, any decrease of it leads to locally degrading the therapeutic response. The largest values of <i>k</i> all correspond to large values of the interaction between the concentration and the fluence.