3D photogrammetry quantifies the size of basal cell carcinoma lesions with submillimeter accuracy: high correlation with lesion response to photodynamic therapy.

SIGNIFICANCE: Noninvasive imaging to accurately measure subtle changes in tumor size is underutilized when assessing therapeutic responses in the skin. During photodynamic therapy (PDT) for basal cell carcinoma (BCC), a better definition of the tumor size threshold for PDT responsiveness is needed.

AIM: We aim to quantitatively demonstrate the first clinical evidence of tumor shrinkage after multiple rounds of PDT using a robust measurement and analysis approach.

APPROACH: Tumors were monitored experimentally using a 3D camera and software system (stereo photogrammetry). A total of 122 BCC tumors in 35 patients were treated with PDT (5-ALA and blue light) in three sessions. Calculated volumes and heights were used to plot changes in tumor size.

RESULTS

In total, 70% of BCC cleared completely. Measured heights correlated with histological tumor depth; average heights were ∼ 10 % to 20% of actual tumor depth. From photogrammetry at baseline, an average height of < 0.15    mm was found to predict a complete therapeutic response. Thus, our 3D morphometric technique provides a surrogate measure of BCC tumor depth that predicts PDT response and is accurate to well below the millimeter level.

CONCLUSIONS

3D photogrammetry can inform the selection of BCC tumors for PDT with exceptionally high spatial accuracy, dramatically better than can be quantified by a clinician.