Short- and long-term normal tissue damage with photodynamic therapy in pig trachea: a fluence-response pilot study comparing Photofrin and mTHPC

Intra-cavity Photodynamic Therapy for malignant tumors of the paranasal sinuses: An in vivo light dosimetry study

BACKGROUND

Photodynamic therapy (PDT) is a promising treatment option for recurrent sinonasal malignancies. However, light administration in this area is challenging given the complex geometry, varying tissue optical properties and difficult accessibility. The goal of this study was to estimate the temporal and spatial variation in fluence and fluence rate during sinonasal mTHPC-mediated PDT. It was investigated whether the predetermined aim to illuminate with a fluence of 20 J⋅cm^-2 and fluence rate of 100 mW⋅cm^-2 was achieved.

METHODS

In eleven patients the fluence and fluence rates were measured using in vivo light dosimetry at the target location during real-time sinonasal PDT. There was a variance in sinonasal target location and type of light diffuser used. In four patients two isotropic detectors were used within the same cavity.

RESULTS

All measurements showed major fluence rate fluctuations within each single isotropic detector probe over time, as well as between probes within the same cavity. The largest fluence rate range measured was 328 mW⋅cm^-2. Only one probe showed a mean fluence rate of ∼100 mW⋅cm^-2. Taken all probes together, a fluence rate above 80 mW⋅cm^-2 was measured in 31 % of the total light exposure; in 22 % it was less than 20 mW⋅cm^-2. Thirty-three percent showed a fluence of at least 20 J⋅cm^-2.

CONCLUSIONS

The current dosimetry approach for sinonasal intra-cavity PDT shows major temporal and spatial variations in fluence rate and a large variance in light exposure time. The results emphasize the need for improvement of in vivo light dosimetry and dosimetry planning.

On the Development of a Light Dosimetry Planning Tool for Photodynamic Therapy in Arbitrary Shaped Cavities: Initial Results

Previous dosimetric studies during photodynamic therapy (PDT) of superficial lesions within a cavity such as the nasopharynx, demonstrated significant intra- and interpatient variations in fluence rate build-up as a result of tissue surface re-emitted and reflected photons, which depends on the optical properties. This scattering effect affects the response to PDT. Recently, a meta-tetra(hydroxyphenyl)chlorin-mediated PDT study of malignancies in the paranasal sinuses after salvage surgery was initiated. These geometries are complex in shape, with spatially varying optical properties. Therefore, preplanning and in vivo dosimetry is required to ensure an effective fluence delivered to the tumor. For this purpose, two 3D light distribution models were developed: first, a simple empirical model that directly calculates the fluence rate at the cavity surface using a simple linear function that includes the scatter contribution as function of the light source to surface distance. And second, an analytical model based on Lambert's cosine law assuming a global diffuse reflectance constant. The models were evaluated by means of three 3D printed optical phantoms and one porcine tissue phantom. Predictive fluence rate distributions of both models are within ± 20% accurate and have the potential to determine the optimal source location and light source output power settings.

Photodynamic therapy with systemic meta-tetrahydroxyphenylchlorin in the treatment of anal intraepithelial neoplasia, grade 3

BACKGROUND AND OBJECTIVE

Anal cancer and preneoplastic anal lesions (anal intraepithelial neoplasia, AIN) rising especially in men having sex with men (MSM). There are no widely accepted treatment standards for AIN. Photodynamic therapy (PDT) using the systemic sensitizer meta-tetrahydroxyphenylchlorin (mTHPC) has the potential to treat the anal area even when the exact borders of the preneoplastic anal lesion cannot easily be visualized.

STUDY DESIGN/MATERIALS AND METHODS

In this prospective intervention study, 15 HIV-positive MSM with AIN 3 were treated in 25 PDT-sessions using mTHPC intravenously administered at drug doses of 0.075-0.15 mg ml(-1) and illumination at 48  hours. The illumination was performed using a custom made applicator using either red light (652 nm) to a measured intended fluence of 10 and 20 J cm(-2) and green light (532 nm) to a measured intended fluence of 105, 210, and 340 J cm(-2) . Red and green illuminations were performed at a (green) equivalent fluence rate of 105 mW cm(-2) .

RESULTS

Initial complete response was seen in 7/25 (28%) of treatments and another 4/25 (16%) initial partial responses. After an average 8 months, recurrences were detected in 7/11 (64%) of sessions that initially showed response. A total 4/25 (16%) showed persistent complete response 6-15 months after green light illumination. Red light illuminations caused more significant side effects combined with no persistent complete response. Reported side effects were intense pain, bloody and purulent rectal discharge, and anal stricture formation, in one patient.

CONCLUSION

The results show that the use of systemic mTHPC is partially effective for the treatment of AIN 3.

Temoporfin (Foscan®, 5,10,15,20-tetra(m-hydroxyphenyl)chlorin)--a second-generation photosensitizer

This review traces the development and study of the second-generation photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin through to its acceptance and clinical use in modern photodynamic (cancer) therapy. The literature has been covered up to early 2011.

Photodynamic Therapy for Airway Stenosis in Rabbit Models

BACKGROUND

Acquired airway stenosis in childhood is resistant to conventional treatment. We examined whether endoscope-assisted photodynamic therapy (PDT) is effective for airway stenosis in animal models of which the pathophysiologic progressions are similar to those of clinical cases showing rapid deterioration.

METHODS

Tracheal mucosa-scraped rabbits were administered IV porfimer sodium (Photofrin; Wyeth K.K., Tokyo, Japan) [2 mg/kg], and the tracheal lesions were irradiated with 630 nm of light emitted from a cylindrical diffuser tip via a transtracheal approach.

RESULTS

Rabbits without PDT (untreated animals) showed dense granulation tissue in the scraped lesion, resulting in airway stenosis complicated with respiratory stridor. PDT ameliorated the degree of airway stenosis (p = 0.008) and reduced respiratory stridor; rabbits that received PDT showed patchy granulation tissue that was only 20 to 30% of the volume of that seen in the untreated animals. Survival time of rabbits that received PDT was significantly prolonged compared with that of untreated animals (p = 0.03).

CONCLUSIONS

PDT was effective for airway stenosis in rabbit models. This suggests that PDT has the potential as a new therapeutic method for airway stenosis originating from granulation tissue.

Accumulation of Photofrin in Lesions of Airway Stenosis Rabbit Models

Airway stenosis in childhood is resistant to conventional treatments. Endoscope-assisted photodynamic therapy (PDT) is a potent candidate for the therapeutic modality owing to the easy approach to the tracheal lesion and low degree of invasiveness. The aim of the present study was to examine whether a photosensitizer preferentially accumulates in the lesion of airway stenosis in order to explore the possible applicability of PDT. The tracheal mucosa of rabbits was scraped off, and the rabbits were intravenously administered with Photofrin. The tissue concentration of Photofrin was quantitatively measured by fluorometric analysis. Granulation formation was seen in the mucosa-deprived lesion, causing airway stenosis. Photofrin concentration in the granulation tissue was four-fold higher than that in the intact trachea and 10-fold higher than that in the liver, spleen, skin and muscle. Photofrin preferentially accumulated in the lesion of airway stenosis. A preliminary experiment on PDT using transtracheal illumination showed an amelioration of airway stenosis, resulting in reduction in respiratory stridor.

In vivo fluence rate measurements during Foscan-mediated photodynamic therapy of persistent and recurrent nasopharyngeal carcinomas using a dedicated light applicator

The objective of this study was to evaluate the performance of a dedicated light applicator for light delivery and fluence rate monitoring during Foscan-mediated photodynamic therapy of nasopharyngeal carcinoma in a clinical phase I/II study. We have developed a flexible silicone applicator that can be inserted through the mouth and fixed in the nasopharyngeal cavity. Three isotropic fibers, for measuring of the fluence (rate) during therapy, were located within the nasopharyngeal tumor target area and one was manually positioned to monitor structures at risk in the shielded area. A flexible black silicon patch tailored to the patient's anatomy is attached to the applicator to shield the soft palate and oral cavity from the 652-nm laser light. Fourteen patients were included in the study, resulting in 26 fluence rate measurements in the risk volume (two failures). We observed a systematic reduction in fluence rate during therapy in 20 out of 26 illuminations, which may be related to photodynamic therapy-induced increased blood content, decreased oxygenation, or reduced scattering. Our findings demonstrate that the applicator was easily inserted into the nasopharynx. The average light distribution in the target area was reasonably uniform over the length of the applicator, thus giving an acceptably homogeneous illumination throughout the cavity. Shielding of the risk area was adequate. Large interpatient variations in fluence rate stress the need for in vivo dosimetry. This enables corrections to be made for differences in optical properties and geometry resulting in comparable amounts of light available for Foscan absorption.

Standardizing dosimetry in esophageal PDT: an argument for use of centering devices and removal of misleading units

A simple standardization of esophageal photodynamic therapy light dosimetry is proposed. Calculations of the effect on local treatment dose of using non-centered diffusing fibers have been made and the methods of calculating light energy dose to the treatment area within a centering balloon are discussed. A requirement for centering devices and standard units of Joules per cm(2) of treatment area are indicated.

Online electrochemical monitoring of nitric oxide during photodynamic therapy

Photodynamic therapy (PDT), as a novel treatment modality, is based on the use of a photosensitizing agent with an excitation light source for the treatment of various malignancies. Its effect is mediated through reactive oxygen species and nitric oxide (NO), which are shown to be present in apoptosis. Individual differences among patients and even in different areas of the same tumor in one patient may cause a major problem with PDT: dose calculation during application of the light. An electrochemical sensor is proposed for online monitoring of NO generation as a solution of this problem. 5-Aminolevulinic acid (ALA) was administered as the photosensitizer in rat cerebellum. An amperometric sensor, selective to NO, was designed and tested both in vitro and in vivo during PDT. ALA-mediated PDT resulted in rapid generation of NO, starting as early as the application of light on the tissue. Simultaneous amperometric recordings have been carried out for 5 min during PDT. The progressive increase in NO concentration peaked at 1.10 min and then the response current began to decrease until it reached a plateau at around 70% of its peak value. This study, for the first time, electrochemically demonstrates the generation of NO during PDT. Rapid and stable responses obtained by the experimental setup confirmed that this method could be used as an online monitoring system for PDT-mediated apoptosis.

Effect of irradiation fluence rate on the efficacy of photodynamic therapy and tumor oxygenation in meta-tetra (hydroxyphenyl) chlorin (mTHPC)-sensitized HT29 xenografts in nude mice

We present direct experimental evidence of the fluence-rate-dependent, radiation-induced variations in intratumor oxygen partial pressure (pO(2)) in HT29 human colon adenocarcinoma xenografts subjected to meta-tetra(hydroxyphenyl)chlorin (mTHPC)-based photodynamic therapy (PDT). The data establish a correlation between tumor oxygenation and treatment outcome. Tumor-bearing mice were injected with 0.3 mg/kg photosensitizer and subjected 72 h later to a 12 J/cm(2) red light dose administered at fluence rates of 5, 30, 90 and 160 mW/cm(2). A significant decrease in mean and median pO(2) was registered at approximately half of the total radiation fluence was delivered in tumors treated at rates of 160 and 90 mW/cm(2). Conversely, with the two lower fluence rates, intratumor pO(2) was maintained at levels comparable to those measured before illumination. Tumor oxygenation values registered shortly after every treatment protocol were at least equal to baseline levels, thus excluding the possibility of significant acute vessel damage during illumination. The tumor regrowth profile correlated with the pO(2) values monitored during irradiation. Tumors treated with fluence rates of 5 and 30 mW/cm(2) exhibited significantly longer tumor quadrupling times than those treated at 160 and 90 mW/cm(2). Improved tumor destruction could be expected by reducing the rate and the extent of oxygen depletion during meta-tetra(hydroxyphenyl)chlorin photodynamic therapy using low fluence rates.

Performance of isotropic light dosimetry probes based on scattering bulbs in turbid media

In a previous paper the calibration of an isotropic light detector in clear media was described and validated. However, in most applications the detector is used to measure light distribution in turbid (scattering) media, that is, in tissues or tissue equivalent optical phantoms. Despite its small diameter (typically 0.8 mm), inserting the detector in a turbid medium may perturb the light distribution and change the fluence rate at the point of measurement. In the present paper we estimate the error in the fluence rate measured by a detector in turbid media after calibration in a clear medium (air), using an optical phantom and detector bulbs of different optical properties. The experimental results are compared with calculations using the diffusion approximation to the transport equation in a spherical geometry. From measurements in optical phantoms and the results of the calculations it appears that introduction of the detector into a water-based turbid medium with refractive index, absorption- and scattering coefficients different from those of the detector bulb may require corrections to the detector response of up to 10-15%, in order to obtain the true fluence rate in that medium. The diffusion model is used to explore the detector response in a number of tissues of interest in photodynamic therapy, using tissue optical properties from the literature. Based on these model calculations it is estimated that in real tissues the fluence rate measured by the detector is up to 3% below the true value.