Comparison of pulsed and continuous wave light in photodynamic therapy of papillomas: an experimental study

Papillomavirus infection of the upper aerodigestive tract is a serious and potentially life-threatening disease which can result in complete respiratory obstruction. Papillomas are the most common benign neoplasm of the larynx in children but have been shown to have an equal propensity to occur in adults. The hallmark of this disease is one of multiple recurrences despite adequate surgical removal, often resulting in a frustrating and prolonged clinical course. Multiple treatment modalities have been used throughout the years, unfortunately with limited success. Recent reports on the treatment of virally induced lesions with photodynamic therapy (PDT) using hematoporphyrin derivative (HPD) or its newly purified form dihematoporphyrin ether (DHE) as photosensitizing agents have appeared in the literature. The successful treatment of papillomas in both the animal model and humans holds great promise. The most commonly used activating light source has been the argon pumped-dye laser (ADL) which produces a continuous wave of coherent light at 630 nm. Although the ADL has proved efficacious in most studies, its cost, size, special cooling water requirements, and large electrical power requirements with limited power output have made it a less than desirable clinical tool. The gold vapor laser (GVL) has been recently proposed as a possible alternate light source for PDT. This laser appears to be more efficient and offers greater power output while requiring less electrical energy than the ADL. The GVL does not produce the same continuous wave light as the ADL but emits pulsed light with high peak power pulses. Some reports have shown a greater tumor response using the GVL at 628 nm, possibly because of greater tissue penetration from the high-peak power pulses. At this time, no studies have investigated the effects of pulsed light during PDT on virally induced papillomas. The present study was conducted to evaluate the efficacy of pulsed light from a GVL as compared to continuous wave light of the ADL in the treatment of papillomas with DHE phototherapy. Statistical analysis of the rate of tumor response, histological changes, and molecular analysis of viral DNA from the involved tissues were performed. Results have shown that the GVL did produce a greater initial rate of tumor response during the first 3 weeks after PDT but did not improve the overall cure rate. Histological and molecular analysis of the treated tissues demonstrated that similar results were obtained when either the ADL or GVL were used as activating light sources.