Photodynamic therapy of tumours in gastroenterology—a review

Ultraviolet and laser radiation safety

Both ultraviolet radiation and laser radiation occupy pmt of the Spectrum designated "optical radiation". Thus, measurement techniques are similar and the same organs (eyes and skin) are at risk from accidental exposure. However, the equipment used to produce ultraviolet and laser radiation differs substantially and the harm caused by each type of radiation is also different. Another significant difference arises from the fact that ultraviolet radiation is natural with associated general population exposure. Consequently, the present article reviews the current status of both ultraviolet and laser radiation with the material divided into two sections where each hazard is considered separately.

In vivo determination of tumor optical parameters in esophageal carcinoma

BACKGROUND AND OBJECTIVE

Dose dependence of light cannot be discussed on the basis of dose alone. On a more fundamental scientific level, the propagation of light in tissue depends on optical parameters of treated tumor tissue. In a prospective, nonrandomized study, in vivo optical parameters of esophageal carcinoma were studied.

STUDY DESIGN/MATERIALS AND METHODS

Nineteen intraoperative measurements of tumor optical parameters in six patients with esophageal carcinoma were performed. After diagnostic work-up and clinical staging, right-sided, posterolateral thoracotomy, and dissection of the esophagus were carried out. The tumor site was exposed and continuous endoluminal irradiation was started during determination of light penetration at the level of the adventitia of the esophagus. The tumors were located exactly between the endoluminal irradiation source and measurement probe in the thoracic cavity. Measurements were performed on tumors having different diameters to show the relationship between tumor diameter, extinction coefficient, and light penetration depth.

RESULTS

The endoluminal incident intensity was 18.5 mW/cm(2). At a tumor diameter of 4, 6, 8, and 9 mm measured intensity of 5.12, 2.28, 0.88 and 0.65 mW/cm(2), an extinction coefficient of 0.321, 0.349, 0.381, and 0.373, as well as penetration depth of 3.21, 2.87, 2.62, and 2. 68 mm, respectively, could be measured. The correlation of tumor optical parameters, tumor diameter, penetration depth, and treatment time were expressed by the relative correction factor for different tumor diameters.

CONCLUSION

The knowledge of tumor optical properties seems to be necessary to adapt dosimetry to the individual situation and manage optimal results of PDT in esophageal cancer.

Long-term survival after photodynamic therapy for esophageal cancer

BACKGROUND/AIMS

Photodynamic therapy (PDT) has been adapted to the endoscopic treatment of digestive cancer, but its indications and efficacy remain uncertain. The aim of this study was to assess its feasibility in the curative treatment of small esophageal tumors.

METHODS

From 1983 to 1991, PDT was used to treat 123 patients with esophageal cancer who were recommended for nonsurgical treatment of squamous cell carcinoma (n = 104) and adenocarcinoma (n = 19). Endoscopic ultrasonography (EUS) was performed in 88 patients; 61 were staged uT1 and 27 were staged uT2. A hematoporphyrin derivative was injected 72 hours before laser irradiation with a 630-nm dye laser. PDT was applied alone in 56 patients and as part of a multimodal protocol in the 67 others.

RESULTS

The complete response rate at 6 months was 87%. The 5-year survival rate was 25% +/- 6%, and the 5-year disease-specific survival rate was 74% +/- 5%. The complete response rate and survival rate were not different (1) between the PDT alone and the PDT multimodal treatment groups, (2) between the adenocarcinoma and squamous cell carcinoma groups, and (3) between the uT1 and uT2 EUS groups. PDT-related complications were esophageal stenosis (n = 43) and cutaneous photosensitization (n = 16).

CONCLUSIONS

In patients with small esophageal tumors who pose high surgical risk, photodynamic therapy is an effective treatment.

Current role of laser and photodynamic therapy in gastrointestinal tumors and analysis of a 10-year experience

Laser energy can be used for a variety of neoplastic diseases including benign tumors, early stage malignancies, and advanced carcinomas, either with curative intent or for palliation. Nd:YAG laser photocoagulation of 168 colorectal adenomas allowed a complete eradication in 70% of cases, after a mean follow-up of 22 months. Advanced and obstructing tumors were treated with Nd:YAG laser to recanalize the lumen. In the upper gastrointestinal tract the recanalization of the lumen by means of laser photocoagulation improved the quality of life and survival. In fact, in our series of 308 patients treated, 1-year survival was 23% in recanalized patients and 7% in nonrecanalized patients. In the lower gastrointestinal tract, 289 cancer patients were treated and an amelioration of symptoms related to the obstruction was obtained in 93%. The current indication for photodynamic therapy is mainly the treatment of flat or ulcerative early stage tumors in the esophagus and stomach of high risk patients. Out of 17 patients treated, 14 were locally cured.

Lasers in surgery

In January 1991 the winter meeting of the Surgical Research Society was held at St. Bartholomew's Hospital and the Institute of Education, London. During the meeting a symposium was held entitled 'Shedding light on lasers'. Speakers addressed the general principles of lasers, laser-tissue interactions and the applications of lasers in gastro-enterology and in vascular disease. This was followed by an open discussion of the current indications, complications and outcome, together with future possible applications for lasers in medicine.

Palliative laser therapy for tumours of the gastrointestinal tract

The argon ion and Nd: YAG lasers were used initially in the mid 1970s to produce haemostasis in acutely bleeding peptic ulcers. With the evolution of treatment techniques, the main area of use of the Nd: YAG laser has now become the palliation of upper and lower GI malignancies. Thermal ablation of tumours may be achieved endoscopically by non-contact laser application at high power, or in the contact mode using artificial sapphire probes at much lower energy levels. Still lower powers can be employed therapeutically using interstitial hyperthermia, and this is best applied endoscopically to exophytic tumour nodules in the gut lumen or to tumours localized ultrasonically in solid organs, such as the liver or pancreas. PDT involves destruction of previously photosensitized tumours by the cytotoxic action of singlet oxygen released on exposure of the neoplastic tissue to light of an appropriate wavelength. Although the theory is attractive, the available experimental and clinical information suggests that treatment should, for the present, be confined to small or early malignancies whose depth of invasion can be verified by endoscopic ultrasound or other imaging techniques. PDT carries the biological advantage of healing by regeneration with preservation of connective tissue stroma, while the Nd: YAG laser causes destruction by thermal coagulation or vaporization and subsequent healing by fibrosis. Laser therapy of GI tumours expands the range of therapeutic endoscopic procedures in a relatively safe and readily repeatable manner which achieves high patient tolerance. By reducing morbidity, mortality and time spent in hospital, it offers significant advantages in the palliative treatment of conditions previously managed by conventional surgery, and also offers opportunities for treatment of previously inoperable disorders. Developments in laser technology and diagnostic imaging techniques are likely to promote laser therapy in the future as a primary treatment modality.