Total Light Fluence Research Articles

Evaluation of Fractionated Photofrin-mediated Photodynamic Therapy Using Different Light Fluences with Reactive Oxygen Species Explicit Dosimetry (ROSED).

Photodynamic therapy (PDT) is an established modality for cancer treatment, and reactive oxygen species explicit dosimetry (ROSED), based on direct measurements of in-vivo light fluence (rate), in-vivo photofrin concentration, and tissue oxygenation concentration, has been proved to provide the best dosimetric quantity which can be used to predict non-fractionated PDT outcome. This study performed ROSED for Photofrin-mediated PDT for mice bearing radiation-induced fibrosacorma (RIF) tumor. As demonstrated by our previous study, fractionated PDT with a 2-hour time interval can significantly improve the long-term cure rate (from 15% to 65% at 90 days), and it tends to increase as the light dose for the first light fraction gets larger. This study focused on further improving the long-term cure rate without introducing apparent toxicity using combinations of different first light fraction lengths and total light fluences. Photofrin was injected through the mouse tail vein at a concentration of 5 mg/kg. After 18~24 hours, treatment was delivered with a collimated laser beam of 1 cm diameter at 630 nm. Mice were treated using two fractions of light fluences with a 2-hour dark interval. Different dose metrics were quantified, including light fluence, PDT dose, and [ROS]rx. In addition, the total reacted [ROS]rx and treatment outcomes were evaluated and compared to identify the optimal light fraction length and total light fluence.

Combination of aerosolized curcumin and UV-A light for the inactivation of bacteria on fresh produce surfaces

There is a critical unmet need to improve microbial safety of fresh fruits and vegetables. Current sanitation approaches cannot achieve >2 log inactivation of bacteria on fresh produce. Thus, there is a need to develop antimicrobial strategies that can consistently achieve >2 logs of bacterial inactivation on the surface of diverse fresh produce. Furthermore it is highly desired that these antimicrobial strategies have reduced environmental impact and are clean label solutions for food products. In this study, we evaluated the combination of curcumin and UV-A light radiation for the inactivation of inoculated E. coli O157:H7 and L. innocua bacterial cells on the surface of spinach, lettuce and tomatoes. Curcumin was deposited on the surface of fresh produce by either aerosolization or conventional spray-atomization methods before exposing the contaminated produce to UV-A light for 10 min (total light fluence of 20.4 kJ m−2). Results showed that the proposed combination of aerosolized or sprayed curcumin and UV-A light radiation can reduce the initial Escherichia coli O157:H7 and Listeria innocua load from 6 log CFU cm−2 to approximately 3 log CFU cm−2 on spinach, lettuce and tomato surfaces. Furthermore, there was no significant difference in bacterial reduction between the different types of inoculated fresh produce surfaces (P > .05). Interestingly, subsequent curcumin deposition and UV-A light exposure cycles were not able to further reduce the bacterial load below the observed threshold of approximately 3 log CFU cm−2. Lastly, the combination of aerosolized curcumin and UV-A light radiation did not affect the color or the texture of the treated fresh produce samples. The findings described in this study illustrate the potential of applying aerosolized or sprayed curcumin under UV-A light illumination to improve microbial safety of fresh produce products.

Reactive Oxygen Species Explicit Dosimetry (ROSED) of a Type 1 Photosensitizer.

Type I photodynamic therapy (PDT) is based on the use of photochemical reactions mediated through an interaction between a tumor-selective photosensitizer, photoexcitation with a specific wavelength of light, and production of reactive oxygen species (ROS). The goal of this study is to develop a model to calculate reactive oxygen species concentration ([ROS]rx) after Tookad®-mediated vascular PDT. Mice with radiation-induced fibrosarcoma (RIF) tumors were treated with different light fluence and fluence rate conditions. Explicit measurements of photosensitizer drug concentration were made via diffuse reflective absorption spectrum using a contact probe before and after PDT. Blood flow and tissue oxygen concentration over time were measured during PDT as a mean to validate the photochemical parameters for the ROSED calculation. Cure index was computed from the rate of tumor regrowth after treatment and was compared against three calculated dose metrics: total light fluence, PDT dose, reacted [ROS]rx. The tumor growth study demonstrates that [ROS]rx serves as a better dosimetric quantity for predicting treatment outcome, as a clinically relevant tumor growth endpoint.

Dosimetry study of PHOTOFRIN-mediated photodynamic therapy in a mouse tumor model.

It is well known in photodynamic therapy (PDT) that there is a large variability between PDT light dose and therapeutic outcomes. An explicit dosimetry model using apparent reacted 1O2 concentration ([1O2]rx) has been developed as a PDT dosimetric quantity to improve the accuracy of the predicted ability of therapeutic efficacy. In this study, this explicit macroscopic singlet oxygen model was adopted to establish the correlation between calculated reacted [1O2]rx and the tumor growth using Photofrin-mediated PDT in a mouse tumor model. Mice with radiation-induced fibrosarcoma (RIF) tumors were injected with Photofrin at a dose of 5 mg/kg. PDT was performed 24h later with different fluence rates (50, 75 and 150 mW/cm2) and different fluences (50 and 135 J/cm2) using a collimated light applicator coupled to a 630nm laser. The tumor volume was monitored daily after PDT and correlated with the total light fluence and [1O2]rx. Photophysical parameters as well as the singlet oxygen threshold dose for this sensitizer and the RIF tumor model were determined previously. The result showed that tumor growth rate varied greatly with light fluence for different fluence rates while [1O2]rx had a good correlation with the PDT-induced tumor growth rate. This preliminary study indicated that [1O2]rx could serve as a better dosimetric predictor for predicting PDT outcome than PDT light dose.

Cherenkov radiation fluence estimates in tissue for molecular imaging and therapy applications

Cherenkov radiation has recently emerged as an interesting phenomenon for a number of applications in the biomedical sciences. Its unique properties, including broadband emission spectrum, spectral weight in the ultraviolet and blue wavebands, and local generation of light within a given tissue, have made it an attractive new source of light within tissue for molecular imaging and phototherapy applications. While several studies have investigated the total Cherenkov light yield from radionuclides in units of [photons/decay], further consideration of the light propagation in tissue is necessary to fully consider the utility of this signal in vivo. Therefore, to help further guide the development of this novel field, quantitative estimates of the light fluence rate of Cherenkov radiation from both radionuclides and radiotherapy beams in a biological tissue are presented for the first time. Using Monte Carlo simulations, these values were found to be on the order of 0.01–1 nW cm−2 per MBq g−1 for radionuclides, and 1–100 μW cm−2 per Gy s−1 for external radiotherapy beams, dependent on the given waveband, optical properties, and radiation source. For phototherapy applications, the total light fluence was found to be on the order of nJ cm−2 for radionuclides, and mJ cm−2 for radiotherapy beams. The results indicate that diagnostic potential is reasonable for Cherenkov excitation of molecular probes, but phototherapy may remain elusive at such exceedingly low fluence values. The results of this study are publicly available for distribution online at www.dartmouth.edu/optmed/.

In-vivo outcome study of HPPH mediated PDT using singlet oxygen explicit dosimetry (SOED).

Type II photodynamic therapy (PDT) is based on the use of photochemical reactions mediated through an interaction between a tumor-selective photosensitizer, photoexcitation with a specific wavelength of light, and production of reactive singlet oxygen. However, the medical application of this technique has been limited due to inaccurate PDT dosimetric methods. The goal of this study is to examine the relationship between outcome (in terms of tumor growth rate) and calculated reacted singlet oxygen concentration ([1O2]rx) after HPPH-mediated PDT to compare with other PDT dose metrics, such as PDT dose or total light fluence. Mice with radiation-induced fibrosarcoma (RIF) tumors were treated with different light fluence and fluence rate conditions. Explicit measurements of photosensitizer drug concentration and tissue optical properties via fluorescence and absorption measurement with a contact probe before and after PDT were taken to then quantify total light fluence, PDT dose, and [1O2]rx based on a macroscopic model of singlet oxygen. In addition, photobleaching of photosenitizer were measured during PDT as a second check of the model. Changes in tumor volume were tracked following treatment and compared to the three calculated dose metrics. The correlations between total light fluence, PDT dose, reacted [1O2]rx and tumor growth demonstrate that [1O2]rx serves as a better dosimetric quantity for predicting treatment outcome and a clinically relevant tumor growth endpoint.

Motexafin gadolinium enhances the efficacy of aminolevulinic acid mediated-photodynamic therapy in human glioma spheroids.

Photodynamic therapy (PDT) has been investigated as a postoperative treatment in patients with high grade gliomas. The purpose of this in vitro investigation was to determine whether motexafin gadolinium (MGd), a known radiation sensitizer, could potentiate the effects of 5-aminolevulinic acid (ALA)-PDT. Human glioma (ACBT) spheroids (250 microm diameter) were incubated in 5-aminolevulinic acid (ALA) with and without MGd and irradiated with 635 nm light for a total light fluence of 6, 12, or 18 J cm(-2) delivered at a fluence rate of 5 mW cm(-2). Spheroid growth was monitored for a period of 4 weeks following each treatment. In another set of experiments, 400-500 microm diameter ACBT spheroids were implanted into a gel collagen matrix and subjected to ALA-PDT (fluence: 3 or 6 J cm(-2)), MGd, or a combination of ALA-PDT and MGd. The migration distance of surviving glioma cells in each treatment group was recorded over a 5-day period. The results showed that MGd interacted with PDT in a synergistic manner resulting in greater cytotoxicity than that achievable with either treatment modality alone. The degree of synergism was shown to increase with increasing light fluence. At the highest light fluence investigated (18 J cm(-2)), the percentage of spheroids demonstrating growth 4 weeks following exposure to MGd, ALA-PDT, or MGd + ALA-PDT was 100%, 75%, and 15%, respectively. The results of cell migration studies revealed that the combination of PDT and MGd produced a significant inhibitory effect on glioma cell migration: the addition of MGd resulted in an approximately three times reduction in migration distance compared with PDT alone. Overall, the results suggest that MGd can potentiate both the cytotoxic and migration inhibitory effects of ALA-PDT and hence, this combined therapeutic approach has the potential to extend treatment volumes in patients with malignant gliomas.

A novel tetracationic phthalocyanine as a potential skin phototherapeutic agent

An amphiphilic tetracationic derivative of Zn(II)-phthalocyanine (RLP068) was prepared by means of chemical synthesis and was showed to possess efficient photophysical and photosensitizing properties against model biological substrates. RLP068 was incorporated into a gel formulation, which allowed its ready penetration into the epidermal layers, but not into the dermis, of both Balb/c and hairless SKH1 mice after 1-2 h of topical deposition. Pharmacokinetic studies showed that the phthalocyanine thus formulated does not enter the general blood circulation. The epidermis-associated amount of phthalocyanine was sufficient to cause an important cutaneous damage upon irradiation with red light (600-700 nm; 100-180 mW/cm(2), 160 J/cm(2)); the latter was confined to the epidermal area with no apparent diffusion to the underlying dermal layers or appearance of photosensitivity in distal skin areas. A systematic investigation of the interplay among the different parameters (deposition time of the formulated phthalocyanine on mouse skin, irradiation fluence rate and total light fluence) allowed us to identify the minimal phototoxic dose, as well as to define irradiation protocols allowing the repeatability of the phototherapeutic treatment. The potential of RLP068 to act as a PDT agent for cutaneous diseases is briefly discussed.

Photodynamic Cytotoxicity Enhancement by Pulsed Diode Laser Irradiation

Summary Fractionated treatment is often used in chemo- and radiotherapy of tumors. Such an approach is likely to improve the therapeutic success also in photodynamic tumor therapy (PDT): discontinuous irradiation with dark intervals of seconds or even milliseconds seems indeed to increase the photodynamic efficiency. Therefore in vitro experiments with a laser light source, which can be programmed for irradiation pulses of different duration and shape, were performed to compare the delivery of regular rectangle pulses of 100 ms to continuous irradiation with respect to the efficiency of PDT. Mammary carcinoma cells (MCF-7) were incubated with the photosensitizers meta-tetrahydroxyphenyl-chlorine (mTHPC)®, Photofrin II® and with 5-aminolevulinic acid (ALA), and exposed to continuous and pulsed laser light. The results obtained from two different cytotoxicity tests (tests for mitochondrial function and membrane integrity) demonstrate that at the same given total light fluence, irradiation with regular on-off light pulses and therefore 50% reduction of the power density causes double cytotoxicity of the tumor cells. This could be explained by diffusion processes of the molecular oxygen, of targets and/ or of oxidised products around the intracellular reactions sites. This method of efficiency increase could be used in clinical application.

Comparison of the In Vivo Photodynamic Threshold Dose for Photofrin, Mono‐ and Tetrasulfonated Aluminum Phthalocyanine Using a Rat Liver Model

The photodynamic threshold dose in normal rat liver was determined from the measured depth of necrosis following surface irradiation. The threshold was determined for the photosensitizing drugs Photofrin and monosulfonated aluminum chlorophthalocyanine, AlPcS1, at 24 h postinjection and was found to be (3.4 x/divided by 1.3) x 10(18) and (8.2 x/divided by 1.5) x 10(18) photons cm-3, respectively, compared with the previously reported value of (38 +/- 2) x 10(18) photons cm-3 for the tri/tetrasulfonated phthalocyanine, AlPcS4. These values were independent of drug concentration or total light fluence. For all three drugs the depth of tissue necrosis decreased as the time between drug and light administration increased from 10 min to 72 h. This decrease can be attributed both to the change in the tissue drug concentration as well as to changes in the efficiency of photodynamic therapy for producing tissue damage, related to the photodynamic necrosis threshold. The threshold values for all three photosensitizers were lowest at 10 min post injection: (1.4 x/divided by 1.4) x 10(18), (1.6 x/divided by 1.3) x 10(18) and (23 x/divided by 1.3) x 10(18) photons cm-3 for Photofrin, AlPcS1 and AlPcS4, respectively. The changes in necrosis threshold with time may be due to an initial change from entirely vascular to a combination of vascular and cellular damage, with later redistribution of the photosensitizer to targets at the subcellular level.

The effects of light spectra fluence, duration and time of application on flowering of Gypsophila

The effectiveness of different lamps and illumination regimes was tested over a wide range of light fluences, thus providing a basis for economic calculations of the optimal illumination regime for winter flowering in Gypsophila. Lamps emitting light in the 550–770-nm range were almost equally suitable. Flowering date was directly related to the logarithm of the total light fluence between 1 and 100 mMol m −2 night −1. The most economical application was to illuminate the plants throughout the night. Cyclic lighting did not provide any saving of energy.