Photodynamic Therapy for Head and Neck Neoplasms

mTHPC-mediated photodynamic therapy for early oral squamous cell carcinoma

Surgery and radiotherapy are standard treatments for early oral squamous cell carcinoma, both resulting in good tumour control. However, neither of these modalities is without consequent functional or cosmetic impairment, and there are patients in whom both are contraindicated. Furthermore, there is a significant risk of metachronous tumours developing in the oral cavity, and salvage or retreatment with either surgery or radiotherapy poses difficulties. Photodynamic therapy (PDT) offers the potential for improved functional and cosmetic outcomes, while achieving comparable tumour control. We conducted an open-label, multicentre study to assess the efficacy and safety of meta-tetrahydroxyphenylchlorin (mTHPC) in patients with early oral cancer. One hundred twenty-one patients received intravenously administered mTHPC, followed 96 hr later by illumination of the tumour surface with 652 nm laser light. Of these patients, 114 were protocol compliant. A complete tumour response was achieved in 85% of protocol-compliant patients (97 of 114 patients). A complete response was maintained in 85% of responders at 1 year and in 77% at 2 years. One- and 2-year actuarial survival rates were 89% and 75%, respectively. In the opinion of the investigators, tumour clearance was accompanied by excellent cosmetic and functional results, without impact on the patients' performance status. Mild-to-moderate pain at the treatment site, a recognised side effect of PDT in the oral cavity, was reported by 82% of patients but was manageable with appropriate analgesia. Mild-to-moderate skin photosensitivity reactions were reported for 13% of patients. mTHPC offers an effective alternative treatment for early oral squamous cell carcinoma. It is associated with excellent functional and cosmetic results and can be used in conjunction with other standard therapies.

Photodynamic therapy for malignant mesothelioma: preclinical studies for optimization of treatment protocols

Effective photodynamic therapy (PDT) depends on the optimization of factors such as drug dose, drug-light interval, fluence rate and total light dose (or fluence). In addition sufficient oxygen has to be present for the photochemical reaction to occur. Oxygen deficits may arise during PDT if the photochemical reaction consumes oxygen more rapidly than it can be replenished, and this could limit the efficacy of PDT. In this study we investigated the influence of the drug-light interval, illumination-fluence rate and total fluence on PDT efficacy for the photosensitizer meta-tetrahydroxyphenylchlorin (mTHPC). The effect of increasing the oxygenation status of tumors during PDT was also investigated. PDT response was assessed from tumor-growth delay and from cures for human malignant mesothelioma xenografts grown in nude mice. Tumor-bearing mice were injected intravenously with 0.15 or 0.3 mg.kg-1 mTHPC, and after intervals of 24-120 h, the subcutaneous tumors were illuminated with laser light (652 nm) at fluence rates of 20, 100 or 200 mW.cm-2. Tumor response was strongly dependent on the drug-light interval. Illumination at 24 h after photosensitization was always significantly more effective than illumination at 72 or 120 h. For a drug-light interval of 24 h the tumor response increased with total fluence, but for longer drug-light intervals even high total fluences failed to produce a significant delay in tumor regrowth. No fluence-rate dependence of PDT response was demonstrated in these studies. Nicotinamide injection and carbogen breathing significantly increased tumor oxygenation and increased the tumor response for PDT schedules with illumination at 24 h after photosensitizer injection.

Optical integrating balloon device for photodynamic therapy

BACKGROUND AND OBJECTIVES

It is difficult to deliver light uniformly and efficiently over the complex shapes presented by various organs for photodynamic therapy (PDT). A balloon delivery device for photodynamic therapy was designed and tested for treatment of various anatomic tissues. The device uses the principle of optical integration by multiple internal diffuse reflections to achieve uniform output illumination.

STUDY DESIGN/MATERIALS AND METHODS

Soft, white, medical-grade silicone balloons were made in various shapes and tested for optical output, uniformity, efficiency, and power capabilities. Balloons were cast to be approximately the shape of the target tissue surface, organ, or cavity. Laser power was introduced into the saline-filled balloon by one or more fiber optics. Devices were constructed and used to illuminate oral mucosa and uterine endometrium for PDT.

RESULTS

The balloon walls had low optical absorption, high diffuse reflectivity (80-95%), and low diffuse transmittance (5-20%) in the 500- to 900-nm wavelength region. Optical efficiencies of 65% were typical with emitted light over complex, nonspherical surfaces. Efficiency increased with inflation of the device, such that irradiance (power/area) at the balloon surface was nearly constant with inflation.

CONCLUSION

Optically integrating balloons can provide highly uniform, efficient light exposure over complex tissue surfaces. Uniformity and irradiance were not strongly affected by balloon inflation, and these robust devices are easy to produce in essentially any shape.

The importance of in situ light dosimetry for photodynamic therapy of oral cavity tumors

BACKGROUND

Photodynamic therapy (PDT) is being evaluated for treatment of localized head and neck cancer. "Light dose" is usually prescribed as incident fluence, which takes no account of reflected and scattered light. This study investigates variations in total tissue fluence for a given incident fluence in the oral cavity.

METHODS

Light dosimetry was performed in 19 patients treated with PDT for cancers in the oral cavity and in 5 volunteers. Illumination was with 652 nm laser light delivered via a microlens. In situ dosimetry was performed with isotropic probes held against the tissue in the illuminated area.

RESULTS

Tissue fluences of 254% to 305% of the incident fluence were measured in the illuminated area in healthy volunteers. In the patient population tissue fluences were 133% to 545% of the incident fluence.

CONCLUSION

The relationship between incident and total tissue fluence depended on the location and pigmentation of the target area and was not predictable. In situ dosimetry during cavity illumination allows for more controlled tissue illumination and should be employed as the basis for light dose prescription in PDT for head and neck cancer.

Photodynamic therapy in women with cervical intraepithelial neoplasia using topically applied 5-aminolevulinic acid

Photodynamic therapy (PDT) is a novel treatment modality that produces local tissue necrosis with laser light after prior administration of a photosensitizing agent. We performed a study of topically applied 5-aminolevulinic acid (5-ALA) in the photodynamic treatment of women with high-grade cervical intraepithelial neoplasia (CIN) using fixed 5-ALA doses and application protocols derived from previous in vitro and in vivo results. Three to 5 hr prior to PDT, 10 ml of a 20% solution of 5-ALA was topically applied using a cervical cap. PDT was performed with irradiation of 100 J/cm2 at an irradiance of 100-150 mW/cm2 with an argon-ion-pumped dye laser at 635 nm. For the endocervix, a specifically designed cylindrical applicator was used. Ten treatment cycles of PDT using 5-ALA were performed in 7 patients with high-grade CIN. Non-thermal laser treatment with 100-150 mW/cm2 was well tolerated. Local toxicity was minor as several patients reported burning sensations and vaginal discharge, but no necrosis, sloughing or scarring occurred. After 3 months, a significant reduction in the size of the ectocervical CIN lesions was noted in only 3 patients, who underwent a second PDT cycle. However, no significant improvement in CIN lesions was noted since cold knife conization revealed persistent CIN in all 7 cases. Therefore, PDT after topical application of 5-ALA using an irradiation of 100 J/cm2 produces only minimal side effects. However, it does not appear to be effective in treating CIN.

What does photodynamic therapy have to offer radiation oncologists (or their cancer patients)?

Major advances have recently been made in photodynamic therapy (PDT) for clinical application, including the development of more powerful photosensitizers and light sources and suitable light applicators. PDT is emerging as an attractive new form of cancer therapy, suitable for treating superficial lesions (less than 1 cm in depth) and carcinoma in situ, or as an adjuvant to surgery for more bulky disease. PDT is therefore complementary to radiotherapy which is better suited to treating larger tumours. There are some qualitative similarities between light distribution in tissue during superficial illumination and ionizing radiation dose distributions during external beam irradiation, or between interstitial PDT and brachytherapy, although the geometric scale is very different (visible light penetrates a maximum of 5-10 mm in tissue). The contribution of scattered light to tissue irradiance is much greater than for ionizing radiation and in situ light dosimetry is very important (although rather complicated) to ensure adequate illumination without over-treating. Dosimetry and treatment planning are highly advanced for ionizing radiation and are routine in all radiotherapy departments. Proper in situ light dosimetry and dose distribution calculation for PDT is in its infancy. Physicists have an important role to play in the further optimization of clinical PDT and much of the infrastructure and expertise present in the radiotherapy department is ideally suited to accommodate PDT. In this review, parallels and contrasts are made between PDT and ionizing radiation for both mechanistic and dosimetric aspects of the therapies. A summary of the most interesting clinical applications is also given.

Photodynamic therapy: an effective, but non-selective treatment for superficial cancers of the oral cavity

It has often been claimed that photodynamic therapy (PDT) produces selective destruction of small cancers without affecting the adjacent normal tissue. The objective of our work was to treat small cancers of the oral cavity with PDT and subsequently excise the treated areas for histological studies of tumour and adjacent normal tissue exposed to the same light dose. Eleven patients with histologically proven T1NO oral squamous-cell carcinomas were treated with PDT, using Photofrin as a sensitiser. The tumours plus a surrounding cuff of normal tissue were exposed to 50 J/cm2 non-thermal laser light at 630 nm delivered by surface illumination and the treated areas subsequently excised. Histological staining and image analysis were used to determine the nature and extent of injury. No macroscopic distinction was evident between tumour and normal tissue exposed to light. Histologically, replacement of superficial epithelium, tumour and connective tissue with a fibrinous necrotic slough was seen. There was also loss of endothelium from small vessels, with haemorrhage and thrombosis. Preservation of subepithelial collagen and elastin was demonstrated with EVG staining. No evidence of selective tumour necrosis was found. Although depth of injury was variable, full thickness mucosal necrosis occurred in all cases.

Photodynamic therapy using 5-aminolevulinic acid for premalignant and malignant lesions of the oral cavity

BACKGROUND

Premalignant changes in the mouth, which are often widespread, are frequently excised or vaporized, whereas cancers are treated by excision or radiotherapy, both of which have cumulative morbidity. Photodynamic therapy (PDT) is another option that produces local tissue necrosis with light after prior administration of a photosensitizing agent. This heals with remarkably little scarring and no cumulative toxicity. This article describes the use of PDT with the photosensitizing agent 5-aminolevulinic acid (ALA) for premalignant and malignant lesions of the mouth.

METHODS

Eighteen patients with histologically proven premalignant and malignant lesions of the mouth were sensitized with 60 mg/kg ALA by mouth and treated with laser light at 628 nanometers (100 or 200 Joules/cm2). The results were assessed macroscopically and microscopically. Biopsies were taken immediately prior to PDT for fluorescence studies, a few days after PDT to assess the depth of necrosis, when healing was complete, and up to 88 weeks later.

RESULTS

The depth of necrosis varied from 0.1 to 1.3 mm, but complete epithelial necrosis was present in all cases. All 12 patients with dysplasia showed improvement (repeat biopsy was normal or less dysplastic) and the treated areas healed without scarring. Some benefit was observed in five of six patients with squamous cell carcinoma, but only two became tumor free (one with persistent mild dysplasia). No patient had cutaneous photosensitivity for longer than 2 days.

CONCLUSIONS

PDT using ALA for dysplasia of the mouth produces consistent epithelial necrosis with excellent healing and is a simple and effective way to manage these patients. Results in invasive cancers are less satisfactory, mainly because the PDT effect is too superficial with current treatment regimens using ALA as the photosensitizing agent.

Diagnostic imaging of the larynx: autofluorescence of laryngeal tumours using the helium-cadmium laser

The use of tissue autofluorescence for the detection and localization of cancer of the larynx is described. In this pilot study, eight patients with probable carcinoma of the vocal folds underwent laryngoscopy in which the tissue autofluorescence spectra of normal and pathologically confirmed tumour tissue were acquired in vivo. Fluorescence images of the suspect areas were also acquired using the LIFE system (Xillix Technologies Corp.). The results suggest that the autofluorescence properties of laryngeal tissue, under 442 nm illumination, are similar to those of bronchial tissue and that the LIFE system has the potential to increase the accuracy of staging of cancer of the larynx and also to allow earlier diagnosis of tumours and their recurrence.

Oral precancer: preventive and medical approaches to management

Leukoplakias are among the most common potentially malignant oral lesions. Some are idiopathic, others are related to habits such as tobacco and/or alcohol use. Medical management includes reducing or abandoning these habits, increasing the intake of fruit and vegetables in the diet, and possibly the use of active agents. Retinoids, carotenoids and topical cytotoxic agents show promise, and newer therapies are on the horizon.

Photodynamic therapy of malignant and premalignant lesions in patients with 'field cancerization' of the oral cavity

The management of patients with 'field cancerization' of the oral mucosa, with multicentric foci of invasion, presents a considerable problem for the head and neck surgeon. Surgical resection of synchronous or metachronous primary squamous cell carcinomas, along with adjacent premalignant lesions, is likely to be associated with considerable mutilation. Photodynamic therapy (PDT) has been shown to be of value in the treatment of superficial tumours in the upper aerodigestive tract, with excellent healing of treated areas. This study reports the use of PDT to treat 11 patients with 'field cancerization' occurring in the oral cavity. Six patients had multiple primary cancers and five had single primary tumours. All had associated areas of leukoplakia. Each received Photofrin 2 mg/kg 48 hours prior to photoirradiation with 50-100 J/cm2 red laser light by surface illumination. Six to eight weeks later treated areas in 10 of the 11 patients showed a complete response to PDT; one patient had areas of residual leukoplakia. Two patients developed further areas of leukoplakia or erythroplakia within 12 months but no patient has had evidence of recurrent invasive carcinoma in the treated areas. Longer term follow-up will be necessary to exclude further recurrence. It is concluded that PDT offers an effective repeatable treatment option, whether on its own or as an adjunct to local excision, for patients with 'field cancerization' of the oral cavity.