In-vivo fluorescence dosimetry of aminolevulinate-based protoporphyrin IX (PpIX) accumulation in human nonmelanoma skin cancers and precancers
2009
PDT is clinically useful for precancers (actinic keratoses; AK) of the skin, but the optimal duration for 5-ALA
application is still controversial. For basal cell carcinoma (BCC) and squamous cell carcinoma (SCC), cure rates remain
inferior to surgical excision. Lack of knowledge about regional levels of PpIX levels within target tissues clearly
contribute to these suboptimal results. To investigate PpIX levels achievable in human skin neoplasias in-vivo, a clinical
study to monitor PpIX accumulation in vivo was performed. PpIX-fluorescence in patients undergoing ALA-PDT for
facial AK was monitored via real-time in-vivo fluorescence dosimetry, with measurements q20 min following
application of 5-ALA (Levulan Kerastick). PpIX accumulation followed linear kinetics in nearly all cases. The slopes
varied widely, and did not correlate with clinical outcome in all patients. Some patients with a low accumulation of
PpIX fluorescence had a good response to therapy, whereas others with high PpIX accumulation required repeat
treatment (although not necessarily of the same lesion). PpIX accumulation rates did correlate to a certain degree with
the overall amount of erythema. We conclude that unknown factors besides PpIX levels must be critical for the response
to treatment. To assess the relationship between PpIX levels in various skin cancers, patients undergoing routine Mohs
surgery for BCC or SCC were measured by in-vivo dosimetry at 2 h after 5-ALA application. Overall, a progressive
increase in PpIX signal during malignant progression was observed, in the following rank order: Normal skin < AK <
SCC ~ BCC.
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