Is the thin layer of methyl aminolevulinate used during photodynamic therapy sufficient?

If the recommended 1.0 mm layer of methyl aminolevulinate (MAL) is used during photodynamic therapy (PDT) of large areas with multiple actinic keratoses (AK) huge amounts of cream are needed.

To report the amount of MAL used for PDT of AK and basal cell carcinomas (BCC) in daily routine. The association of protoporphyrin IX (PpIX) fluorescence and thickness of MAL was investigated in a randomized paired study in healthy volunteers.

Amount of cream used per cm(2) during conventional and daylight PDT was recorded. In 16 healthy volunteers, 0.1 mm, 0.2 mm, 0.5 mm and 1.0 mm MAL cream were applied for 3 h on tape-stripped areas on each forearm randomized to light-permeable or light-impermeable occlusion. PpIX fluorescence was measured.

Less than 0.4 mm MAL was used during PDT of BCC and 0.2 mm for AK. No difference in PpIX fluorescence was found between the different thicknesses of MAL using light-impermeable occlusion.

In daily routine <0.4 mm MAL was used during PDT of BCC and 0.1-0.2 mm MAL during PDT of AK. The recommended 1.0 mm MAL did not result in a higher accumulation of PpIX compared to thinner MAL layers after light-impermeable occlusion for 3 h.