Photodynamic therapy

Revisiting photodynamic therapy dosimetry: reductionist & surrogate approaches to facilitate clinical success

Photodynamic therapy (PDT) can be a highly complex treatment, with many parameters influencing treatment efficacy. The extent to which dosimetry is used to monitor and standardize treatment delivery varies widely, ranging from measurement of a single surrogate marker to comprehensive approaches that aim to measure or estimate as many relevant parameters as possible. Today, most clinical PDT treatments are still administered with little more than application of a prescribed drug dose and timed light delivery, and thus the role of patient-specific dosimetry has not reached widespread clinical adoption. This disconnect is at least partly due to the inherent conflict between the need to measure and understand multiple parameters in vivo in order to optimize treatment, and the need for expedience in the clinic and in the regulatory and commercialization process. Thus, a methodical approach to selecting primary dosimetry metrics is required at each stage of translation of a treatment procedure, moving from complex measurements to understand PDT mechanisms in pre-clinical and early phase I trials, towards the identification and application of essential dose-limiting and/or surrogate measurements in phase II/III trials. If successful, identifying the essential and/or reliable surrogate dosimetry measurements should help facilitate increased adoption of clinical PDT. In this paper, examples of essential dosimetry points and surrogate dosimetry tools that may be implemented in phase II/III trials are discussed. For example, the treatment efficacy as limited by light penetration in interstitial PDT may be predicted by the amount of contrast uptake in CT, and so this could be utilized as a surrogate dosimetry measurement to prescribe light doses based upon pre-treatment contrast. Success of clinical ALA-based skin lesion treatment is predicted almost uniquely by the explicit or implicit measurements of photosensitizer and photobleaching, yet the individualization of treatment based upon each patients measured bleaching needs to be attempted. In the case of ALA, lack of PpIX is more likely an indicator that alternative PpIX production methods must be implemented. Parsimonious dosimetry, using surrogate measurements that are clinically acceptable, might strategically help to advance PDT in a medical world that is increasingly cost and time sensitive. Careful attention to methodologies that can identify and advance the most critical dosimetric measurements, either direct or surrogate, are needed to ensure successful incorporation of PDT into niche clinical procedures.

Uptake and cell-killing activities of a series of Victoria blue derivatives in a mouse mammary tumour cell line

The triarylmethane dye Victoria blue BO (VBBO) is a known photosensitizer which has been shown to induce a cytotoxic response in vitro. Several novel Victoria blue derivatives, with varying physicochemical properties, have been compared to VBBO, with respect both to dark toxicity and phototoxicity, on a mouse mammary tumour cell line, EMT6. Photosensitizer uptake was observed using confocal fluorescence microscopy. The chemical differences, particularly in the naphthyl substitution of the derivatives were shown to alter the light:dark toxicity differential and the uptake of the photosensitizers.

Blood pO2 and blood flow at the optic disc

A fundus camera-based phosphorometer to noninvasively and quasicontinuously measure the blood partial pressure of oxygen (pO(2,blood)) in the microvasculature of the pig optic nerve using the principle of the phosphorescence quenching by O(2) is described. A porphyrin dye is injected into the venous circulation and the decay of its phosphorescence emission is detected locally in the eye, after excitation with a flash of light. Combined with blood flow measurements by means of a laser Doppler flowmeter mounted on the phosphorometer, we demonstrate the capability of the instrument to determine the time course of optic nerve blood flow and pO(2,blood) in response to various physiological stimuli, such as hyperoxia and hypercapnia. This instrument appears to be a useful tool for the investigation of the oxygenation of the optic nerve.

Lasers in veterinary medicine--where have we been, and where are we going?

Future use of lasers in medicine depends on the active participation of veterinarians in the inception and development of new devices that meet the needs of the entire medical profession. The sensible clinical approach that must be taken every day in the practice of veterinary medicine equips the veterinarian with a unique ability to understand the practical applications of biomedical lasers. Veterinary medicine can and should be in the forefront during these exciting times, adding an essential dimension to development of this twenty-first century technology.

Photodynamic therapy in dermatology

The combination of light and chemicals to treat skin diseases is widely practiced in dermatology. Within this broad use of light and drugs, in recent years the concept of photodynamic therapy (PDT) has emerged. PDT is a promising modality for the management of various tumors and nonmalignant diseases, based on the combination of a photosensitizer that is selectively localized in the target tissue and illumination of the lesion with visible light, resulting in photodamage and subsequent cell death. Moreover, the fluorescence of photosensitizing compounds is also utilized as a helpful diagnostic tool for the detection of neoplastic tissue. Intensive basic and clinical research culminated in the worldwide approval of PDT for bladder, esophageal, and lung cancer. The expanding use of this relatively new therapeutic modality in dermatology at many centers around the world has revealed its efficacy for the treatment of cutaneous precancer and cancer, as well as selected benign skin disorders. The following article summarizes the main principles of PDT considering the most recent developments and provides a comprehensive synopsis of the present status of the use of PDT in dermatology. (J Am Acad Dermatol 2000;42:389-413.)

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to describe the basic concepts of PDT, including fundamental knowledge of the most relevant photosensitizers, the light sources, the mechanisms involved in PDT-mediated cell destruction, as well as the indications and limitations of photodynamic treatment of skin diseases.

Use of photodynamic therapy for the treatment of squamous cell carcinoma of the soft palate

A 53-year-old white woman presented with a 5-month history of throat pain. The soft palate was biopsied and histological examination confirmed the diagnosis of infiltrating squamous cell carcinoma. She refused surgery and radiotherapy and was therefore offered photodynamic therapy which she accepted. She was treated with 20 J/cm2 at 100 m W/cm2 over a 3 cm area. She was discharged three days later having made an uncomplicated recovery, though substantial analgesia was required. Healing was complete after 2 months, with no loss of palatal function and at most recent follow-up (16 months) there was no sign of residual disease and she remained well.

Preliminary results of photodynamic therapy for recurrent nasopharyngeal carcinoma

Photodynamic therapy (PDT) is a promising new modality in the treatment of cancer. In Hong Kong where nasopharyngeal carcinoma (NPC) is endemic, radiotherapy has been the primary treatment of choice. For recurrent disease after radiotherapy, there is no effective treatment. This latter report summarizes our initial experience in using PDT for these patients. Twelve patients (three females and nine males) with ages ranging from 33 to 65 years were treated with an infusion of hematoporphyrin derivative (5 mg/kg) 48-72 h before exposure to 200 J/cm2 light (wavelength, 630 nm) delivered from a gold vapor laser. All 12 patients showed a dramatic response as judged by computed tomography or magnetic resonance imaging at 6 months post-PDT. Of the eight patients in whom cure was aimed for, three remained disease-free at 9-12 months after a single treatment. Three of the remaining four patients achieved useful palliation. Skin hypersensitivity occurred in two patients and was the only significant complication encountered. This experience indicates that PDT can be an encouraging palliative or definitive management for recurrent superficial NPC.

Photothrombosis of retinal and choroidal vessels in rabbit eyes using chloroaluminum sulfonated phthalocyanine and a diode laser

BACKGROUND AND OBJECTIVES

Photothrombosis is a relatively new photodynamic application leading to vascular occlusion. In the current work the effectiveness of phthalocyanine and a diode laser in photothrombosis of normal retinal and choroidal vessels was evaluated.

STUDY DESIGN, MATERIALS AND METHODS

Big retinal vessels of temporal myelin wing were irradiated using a 670 nm diode laser (2 mW, 0.5 mm2) after the injection of chloroaluminum sulfonated phthalocyanine (5 mg/kg) in twenty albino rabbits. Animals were followed up to a maximum of 7 months using fundus photography, fluoroangiography, and histology.

RESULTS

Photothrombosis of the irradiated retinal vessels and of underlying choroidal vessels resulted in all treated eyes after 13 to 17.5 min of irradiation. The retinal vessels were patent again by the 7th day after the procedure. Choroidal vessels remained closed during the whole follow-up period. Light and electron microscopy demonstrated occupation of irradiated choroidal and retinal vessels by platelet thrombi. Damage of endothelial cell structure of these vessels could be seen. Outer retinal and RPE damage localized at irradiation area was observed.

CONCLUSION

The combination of phthalocyanine with a low power diode laser is a simple and effective way for the induction of photodynamic thrombosis in fundus vessels.

Management of cutaneous symptoms

OBJECTIVE

To provide a review of the problems of malignant skin lesions, skin changes associated with cancer therapy, and required nursing care.

DATA SOURCES

Published articles and book chapters that pertain to skin, malignant skin lesions, cutaneous toxicity from cancer therapy, pressure ulcers, and nursing care.

CONCLUSIONS

Cutaneous symptoms as a result of the disease process or its treatment (chemotherapy, cytokines, radiation) interfere with optimal functioning and quality of life. The management and nursing care of malignant skin lesions, hyperpigmentation, changes in sensation, hypersensitivity reactions, acral erythema, erythema, desquamation, and pressure ulcers provide major treatment challenges for the oncology nurse.

IMPLICATIONS FOR NURSING PRACTICE

Skilled assessment, prevention, intervention, and evaluation of skin problems can reduce the difficulties patients and family members encounter with cutaneous symptoms and promote self-care and optimal functioning.

Enhancement of photodynamic therapy with 5-aminolaevulinic acid-induced porphyrin photosensitisation in normal rat colon by threshold and light fractionation studies

5-Aminolaevulinic acid (ALA)-induced prophyrin photosensitisation is an attractive option for photodynamic therapy (PDT) since skin photosensitivity is limited to 1-2 days. However, early clinical results on colon tumours using the maximum tolerated oral dose of 60 mg kg-1 showed only superficial necrosis, presumably owing to insufficient intratumoral porphyrin levels, although inadequate light dosimetry may also be a factor. We undertook experiments using ALA, 25-400 mg kg-1 intravenously, to establish the threshold doses required for a PDT effect. Laser light at 630 nm (100 mW, 10-200 J) was delivered to a single site in the colon of photosensitised normal Wistar rats at laparotomy. The animals were killed 3 days later and the area of PDT-induced necrosis measured. No lesion was seen with 25 mg kg-1. The lesion size increased with larger ALA doses and with the light dose but little benefit was seen from increasing the ALA dose above 200 mg kg-1 or the light dose above 100 J. Thus there is a fairly narrow window for optimum doses of drug and light. Further experiments showed that the PDT effect can be markedly enhanced by fractionating the light dose. A series of animals was sensitized with 200 mg kg-1 ALA and then treated with 25 J. With continuous irradiation, the lesion area was 13 mm2, but with a single interruption of 150 s the area rose to 94 mm2 with the same total energy. Results were basically similar for different intervals between fractions (10-900 s) and different numbers of fractions (2-25). This suggests that a single short interruption in the light irradiation may dramatically reduce the net light dose required to achieve extensive necrosis.

Applications of laser technology in breast cancer therapy

Breast cancer is an increasingly common problem affecting one in nine women. The optimal management of carcinoma of the breast remains controversial. This paper reviews the rationale for the use of laser technology in the treatment of primary and advanced breast cancer. The CO2 laser has several properties which make it advantageous for breast surgery. The technical details for optimal laser utilization are presented. Experimental evidence documents a marked reduction of local tumor recurrence following surgery with lasers. Preliminary human studies suggest that laser use lengthens the disease-free interval and may decrease local recurrence. Interstitial laser therapy holds promise for use in the treatment of locally advanced breast tumors and has been suggested by some as a potential modality for the primary therapy of breast cancer. The clinical use of lasers in the treatment of breast cancer is justified.

Phthalocyanine mediated photodynamic thrombosis of experimental corneal neovascularization: effect of phthalocyanine dose and irradiation onset time on vascular occlusion rate

The aim of this study was to evaluate the possible influence of phthalocyanine dose and of time interval between phthalocyanine injection and irradiation commencement on the rate of experimental corneal neovascularization photodynamic thrombosis in albino rabbits. New corneal vessels were irradiated with a diode laser (670 nm, 2 mW) after the intravenous injection of chloroaluminum sulfonated phthalocyanine. Different animals were irradiated either 5 min after the injection of different phthalocyanine doses (3, 6, 8, 12, or 14 mg/kg), or at different times (5 min, 24 h, or 58 h) after a standard phthalocyanine dose (3 mg/kg) injection. Irradiation time necessary for vascular occlusion was recorded. Decrease of phthalocyanine dose as well as delay of irradiation onset resulted in a statistically significant increase of irradiation time. Electron and light histological examination revealed platelet thrombi inside irradiated corneal new vessels. Damage in the vascular endothelial cell membrane and in intercellular contact structure was noted, leading to disorganization of the endothelial cells layer and death of most endothelial cells. These results indicate that both early commencement of irradiation after phthalocyanine injection and phthalocyanine dose increase accelerate the rate of phthalocyanine mediated corneal neovascularization photodynamic thrombosis. Thrombosis seems to result from photochemically induced vascular endothelial cell damage.