Due to the increasing complexity very precise evaluation
of the effective delivered dose in PDT seems today hardly reachable challenge.
Although the use of photosensitizer photobleaching in implicit dosimetry
is attractive in principle, there are a number of problems which must be
resolved for it to become routinely useful. We have tried to add few additional
aspects related to photobleaching of sensitizer as dose metrics, which
is widely discussed in the paper of Wilson et al
Other factor, which may have significant influence
on the use of photobleaching as dose metrics, is pH of the environment.
This is especially important for photosensitizers preferentially localizing
in lysosomes. The lower pH can increase the photostability of sensitizer
and change the coupling of the photobleaching with biological effect.
This work in part was supported by the Lithuanian State Science and Education Foundation and the Norwegian Research Council. S.B. and J.P. are indebted to Prof.J.Moan for the opportunity to perform experiments with ALA-induced porphyrins in his lab and for the fruitful discussions.