Pulsed ultrasound measurements of depth and regression of basal cell carcinomas after photodynamic therapy: relationship to probability of 1-year local control

Abstract

The regression of clinical basal cell carcinoma (BCC) after photodynamic therapy (PDT) is poorly understood, but is potentially important when, as is increasingly the case, a second treatment is contemplated. High-frequency pulsed ultrasound provides noninvasive information on skin and lesion thickness. To relate pulsed ultrasound measurements before and after PDT to the probability of local control of BCC by PDT. Skin thickness and lesion thickness were measured by 20-MHz pulsed ultrasound in 181 patients diagnosed as having BCC. Maximal lesion thickness was determined by repeatedly sampling the BCCs. Measurements were made immediately prior to PDT with aminolaevulinic acid plus 630 nm visible light, and then at 1, 6 and 12 months. Skin thickness in individual patients did not vary with time in this study (mean +/- SD 2.3 +/- 0.6 mm; P = 0.8). In contrast, BCC mean +/- SD maximal thickness 4-6 weeks after PDT was significantly smaller than pretreatment (0.6 +/- 0.8 mm vs. 1.3 +/- 0.8 mm; P < 0.001). The overall probability of 1-year local control fell from 85% when only BCCs </= 1.5 mm thick were considered, to 75% when BCCs up to 3 mm were included. Ultrasound measurement of maximal pretreatment BCC thickness strongly predicts the probability of local control, defined clinically, at 1 year after a single PDT treatment. The degree of regression at 4-6 weeks is additionally predictive.