Fluorescence Diagnostics of Basal Cell Carcinomas Comparing Methyl-aminolaevulinate and Aminolaevulinic Acid and Correlation with Visual Clinical Tumour Size

Abstract

Fluorescence diagnostics based on aminolaevulinic acid (ALA) fluorescence has been suggested as an in vivo pre-surgical tool for tumour demarcation. We performed fluorescence diagnostics of 35 basal cell carcinomas (BCCs) undergoing photodynamic therapy (PDT) using methylaminolaevulinate (MAL). In addition, a semi-automated thresholding algorithm was implemented to detect the potential tumour region. The mean tumour fluorescence contrast was found to be 1.65±0.06 during the first MAL-PDT session, and increased to 1.84±0.07 at the second treatment (p < 0.01). This could imply that disruption of the skin barrier and inflammatory responses after the first session of PDT led to higher accumulation of protoporphyrin IX during the second session of PDT. The tumour areas detected based on fluorescence in small BCCs (< 1 cm2) were in general (n = 18/23) larger than the visual clinical tumour size. In addition, the fluorescence contrast using MAL (1.65±0.06) was found to be significantly higher (p<10–4) than the contrast (data from previous study) after application of ALA (1.20±0.06). Thus, MAL generally provides higher tumour contrast than ALA in BCCs, and should be preferred for use in fluorescence diagnostics. Correlation between fluorescence, lack of treatment response and/or pain was not observed.