Coralline photosynthetic physiology across a steep light gradient.

Coralline algae (CA) are globally distributed and fulfil many important roles within coastal ecosystems. In this study, photosynthetically active radiation (PAR) measured for 616 days at 2 and 10 m in a temperate subtidal kelp forest in southern New Zealand provided context to photosynthesis vs. irradiance relationships for, and pigment concentrations of, an articulated coralline alga, Arthrocardia sp. and a crustose coralline species assemblage within the Hapalidiales order. The maximum photosynthetic rate Pmax of the Arthrocardia sp. (20.38 ± 2.38 µmol O2. gDW-1 h-1) was significantly higher than the Pmax of crustose coralline spp. (3.72 ± 0.74 µmol O2. gDW-1 h-1) at the same 2 m stratum. Pigment concentration of Arthrocardia sp. was significantly higher than that of crustose coralline spp. at the same depth, while pigment concentration of crustose coralline spp. at 2 and 10 m were not significantly affected by depth. The photosynthetic characteristics of these coralline algae represent a shade acclimated organism with low saturation irradiance (all Ek < 100 µmol photons m-2 s-1). Despite sevenfold difference in average daily dose between 2 and 10 m there was no significant effect of depth on the photosynthetic performance of crustose coralline algae measured. The lack of evidence for acclimation to low light could be because periods of clear water provide enough light to maintain photosynthesis, lower energetic requirements of species found at depth or constraints on the synthesis of photosynthetic pigments at greater depth.

Monte Carlo simulations of photodynamic therapy in human blood model.

This study aims to simulate a therapeutic plan for a normal human blood model under various patho-physiological conditions, such as the development of leukemia/blood diseases, by means of Monte Carlo multilayered simulation. The photosensitizing compound selectively accumulates in the target cells. A superficial treatment of a blood sample was performed at different ratios of oxygen saturation ([Formula: see text]) under the concentration ([Formula: see text] = 30 µM) effect of merocyanine 540 (MC540) in the blood irradiation. This was done under the application of visible light of wavelength ~ [Formula: see text] at an exposure time ~ 60 s. The dose of photodynamic therapy (PDT) was evaluated for the biological damage, leading to necrosis and blood damage during the treatment. In addition, the effect of PDT treatment response in the blood is related to hemoglobin oxygen saturation, resulting in an excellent relationship between the changes caused by the treatment in the blood at a peculiar oxygen saturation rate (for the highest response: [Formula: see text] 50%) and a light dose (LD) of 3.83 [Formula: see text] above the minimal toxicity of normal tissues. The photodynamic dose is related to the depth of necrosis and the time of treatment for the achievement of the LD delivery at the PDT of blood.

Effects of riboflavin and ultraviolet light treatment on pathogen reduction and platelets.

BACKGROUND: Pathogen reduction technology has become an accepted method for limiting transfusion-transmitted infections (TTIs). Riboflavin and ultraviolet light (RUV) treatment of platelets (PLTs) is an optional means of pathogen inactivation owing to its safety, effectiveness, and ease of use. However, the literature on effects of ultraviolet (UV) light spectra and doses on pathogen reduction is still contradictory. METHODS: We tested the effectiveness of killing Escherichia coli following RUV exposure with one broad-spectrum and two narrow-spectrum light sources centered at 311 and 365 nm and at successively higher doses by limited dilution survival assays. After comparing the effectiveness of E coli and phage inactivation (n = 6) and the changes in PLT count and metabolism caused by RUV treatment with optimized UV light at increasing doses, we confirmed our results by using four model virus systems that represent common TTIs, as well as PLT function and activation assays at an optimized light dose. RESULTS: The narrow-spectrum UV, centered at 311 nm, optimally reduced the E coli titer with a light dose ≥8.11 J/mL, resulting in the same trend of E coli and phage reduction at different light doses. At 8.11 J/mL, 311-nm narrow-spectrum UV had a good inactivation effect on E coli and phages, eliminating many viruses, and resulted in acceptable PLT quality after RUV treatment and during storage for 4 days. CONCLUSIONS: Our data suggest restricting exposure to narrow-spectrum UV centered at 311 nm can increase E coli elimination and potentially optimize virus titer reduction without significantly compromising PLT quality.

A New Optical Method for Online Monitoring of the Light Dose and Dose Profile in Photodynamic Therapy.

BACKGROUND AND OBJECTIVES: Photodynamic therapy (PDT) has gained widespread popularity in the last decades because of its distinctive advantages over the other commonly used cancer treatments. PDT dosimetry is a crucial factor in achieving a good optimization of PDT treatment planning. PDT dosimetry is a complex task since light dose as well as photosensitizer and oxygen concentrations in tissue need to be measured (ideally continuously) to be able to fully characterize the biological response. Light dose in PDT is routinely measured by the optical fibers that provide dose data at a limited number of discrete points and are not able to capture spatial dose profiles. The objective of this study is to propose and develop a new optical method for online monitoring of the dose profile data for PDT. STUDY DESIGN/MATERIALS AND METHODS: Using the digital holography technique, first, the general sketch of an experimental setup for PDT light dosimetry is provided. The theory behind the proposed method for using the experimental setup in PDT light dosimetry is fully described, and its limits of validity are determined. In a proof of principle study, the ability of the method for online monitoring of the absorbed light dose profile in PDT is evaluated by a simple experimental setup. RESULTS: The experimental results confirm the usefulness of the proposed method in providing continuous online dose profiles. The absorbed light dose profiles from an infrared light source in a quartz cell containing water are measured and shown. The depth-dose curves are extracted and it is shown that how these dosimetric data can be used for assisting the physicians in determining the appropriate spatiotemporal characteristics for treating the infected tissues and solid tumors with the required light dose amounts. A conversion relation is also derived for transforming the measured light dose with the proposed method to the most frequently used dose values by PDT practitioners, in terms of light power per square area. CONCLUSIONS: There is no restriction in using the method with other commonly used light sources in PDT, like light-emitting diodes and filtered lamps, with different wavelengths in visible or infrared regions of the spectrum. More complex experimental setups can be used in future studies to study the role of accumulated photosensitizers in malignant tissues. The proposed method in this study can also be used for light dose monitoring in other biomedical applications, where light is used for treating special diseases, and patients must receive sufficient amounts of light dose. Lasers Surg. Med. © 2019 Wiley Periodicals, Inc.

Comparison of 10 efficient protocols for photodynamic therapy of actinic keratosis: How relevant are effective light dose and local damage in predicting the complete response rate at 3 months?

BACKGROUND: Topical photodynamic therapy is an established treatment modality for various dermatological conditions, including actinic keratosis. In Europe, the approved protocols for photodynamic therapy of actinic keratosis involve irradiation with either an Aktilite CL 128 lamp or daylight, whereas irradiation with the Blu-U illuminator is approved in the United States. Many other protocols using irradiation by a variety of light sources are also clinically efficient. OBJECTIVES: This paper aims to compare 10 different protocols with clinically proven efficacy for photodynamic therapy of actinic keratosis and the available spectral irradiance of the light source. Effective irradiance, effective light dose, and local damage are compared. We also investigate whether there is an association between the complete response rate at 3 months and the effective light dose or local damage. METHODS: The effective irradiance, also referred to as protoporphyrin IX-weighted irradiance, is obtained by integrating the spectral irradiance weighted by the normalized absorption spectrum of protoporphyrin IX over the wavelength. Integrating the effective irradiance over the irradiation time yields the effective light dose, which is also known as the protoporphyrin IX-weighted light dose. Local damage, defined as the total cumulative singlet oxygen molecules produced during treatment, is estimated using mathematical modeling of the photodynamic therapy process. This modeling is based on an iterative procedure taking into account the spatial and temporal variations in the protoporphyrin IX absorption spectrum during treatment. RESULTS: The protocol for daylight photodynamic therapy on a clear sunny day, the protocol for daylight photodynamic therapy on an overcast day, the photodynamic therapy protocol for a white LED lamp for operating rooms and the photodynamic therapy protocol for the Blu-U illuminator perform better than the six other protocols-all involving red light illumination-in terms of both effective light dose and local damage. However, no association between the complete response rate at 3 months and the effective light dose or local damage was found. CONCLUSIONS: Protocols that achieve high complete response rates at 3 months and low pain scores should be preferred regardless of the effective light dose and local damage. Lasers Surg. Med. 50:576-589, 2018. © 2018 Wiley Periodicals, Inc.

Light dose versus rate of delivery: implications for macroalgal productivity.

The role of how light is delivered over time is an area of macroalgal photosynthesis that has been overlooked but may play a significant role in controlling rates of productivity and the structure and persistence of communities. Here we present data that quantify the relative influence of total quantum dose and delivery rate on the photosynthetic productivity of five ecologically important Phaeophyceae species from southern New Zealand. Results suggested that greater net oxygen production occurs when light is delivered at a lower photon flux density (PFD) over a longer period compared to a greater PFD over a shorter period, given the same total dose. This was due to greater efficiency (α) at a lower PFD which, for some species, meant a compensatory effect can occur. This resulted in equal or greater productivity even when the total quantum dose of the lower PFD was significantly reduced. It was also shown that light limitation at Huriawa Peninsula, where macroaglae were sourced, may be restricting the acclimation potential of species at greater depths, and that even at shallow depth periods of significant light limitation are likely to occur. This research is of particular interest as the variability of light delivery to coastal reef systems increases as a result of anthropogenic disturbances, and as the value of in situ community primary productivity estimates is recognised.

Comparative study of the effect of different exposure parameters of 635nm diode laser and toluidine blue O in eliminating Aggregatibacter actinomycetemcomitans biofilm from titanium implant surfaces.

BACKGROUND: The aim of this study was to investigate the effects of antimicrobial photodynamic therapy (PDT) using 635 nm diode laser irradiation with an energy density of 6 to 30 J/cm2 and toluidine blue O (TBO) as a photosensitizer on the viability of Aggregatibacter actinomycetemcomitans attached to the surface of titanium implants. MATERIALS AND METHODS: Titanium implants contaminated with A. actinomycetemcomitans were treated with TBO alone or in combination with different exposure parameters (light doses of 6 - 30 J/cm2 at 635 nm) and 0.2 % chlorhexidine (CHX). After treatment, colony forming units (CFUs)/ml were determined to assess PDT efficacy. The structure of the biofilm of A. actinomycetemcomitans was analyzed by field emission scanning electron microscopy (FESEM). RESULTS: Under optimal conditions, the colony count was reduced by ∼90 %. Treatment with CHX was somewhat more effective (colony formation was reduced by ∼95 %), but this agent has adverse effects that can be avoided with PDT. CONCLUSION: This study confirms the efficacy of PDT against A. actinomycetemcomitans depending on the light dose. Treatment with TBO + 635 nm diode laser has an effect that may be equivalent to that of CHX, but perhaps with fewer adverse effects.

Light dose effect of photodynamic therapy on growth inhibition and apoptosis induction in non-small cell lung cancer: A study in nude mouse model.

BACKGROUND: Photodynamic therapy (PDT) is receiving increasing attention in treating non-small cell lung cancer (NSCLC) worldwide, but in clinical practice, the relationship between treatment effect and PDT light dose in NSCLC remains unclear. Therefore, we aimed to determine the optimal light dose for PDT by exploring molecular biomarkers and evaluating tumor growth data. METHODS: We applied bioinformatics to identify promising genes and pathways in NSCLC and PDT. Then, the human lung adenocarcinoma cell line A549-bearing BALB/c nude mice were treated with hematoporphyrin derivative (HPD, 3 mg/kg) that is currently used widely for lung cancer treatment in the world even with photosensitization issues. After 48 h, tumor-bearing mice were irradiated superficially at doses of 100, 200, 300, 400, and 500 J/cm2. The tumor growth data and apoptotic molecules were assessed and calculated. RESULTS: Bioinformatics results indicated that the apoptosis pathway was significantly enriched and caspase 3 was the most promising biomarker on prognosis in NSCLC-PDT. Compared to the untreated group, there was no difference in the relative tumor volume (RTV) of the 100 J/cm2 group, while the RTV of the other treatment groups (200-500 J/cm2) was significantly lower. In the 100 J/cm2 group, there were significant differences in the complete remission (CR, 0 %) and the percentage of tumor growth inhibition rate (TGI%) over 75 % (20 %) compared with the other treatment groups, especially the 300 and 400 J/cm2 groups (CR 70 %; TGI% 90 %). In the 300 and 400 J/cm2 groups, the expression of caspase 3, cleaved-caspase 3, PARP1, and Bax was increased significantly, while Bcl-2 expression was significantly lower. CONCLUSIONS: Moderate doses of PDT (300 or 400 J/cm2) are more effective than low (100 or 200 J/cm2) or high doses (500 J/cm2) in the A549 tumor-bearing mice model. Since the A549 tumor is more akin to human tumors in pathological behavior, these experimental data may contribute to improving HPD-PDT illumination protocols for favorable clinical outcomes.

A Monte Carlo simulation for Moving Light Source in Intracavity PDT.

We developed a simulation method for modeling the light fluence delivery in intracavity Photodynamic Therapy (icav-PDT) for pleural lung cancer using a moving light source. Due to the large surface area of the pleural lung cavity, the light source needs to be moved to deliver a uniform dose around the entire cavity. While multiple fixed detectors are used for dosimetry at a few locations, an accurate simulation of light fluence and fluence rate is still needed for the rest of the cavity. We extended an existing Monte Carlo (MC) based light propagation solver to support moving light sources by densely sampling the continuous light source trajectory and assigning the proper number of photon packages launched along the way. The performance of Simphotek GPU CUDA-based implementation of the method - PEDSy-MC - has been demonstrated on a life-size lung-shaped phantom, custom printed for testing icav-PDT navigation system at the Perlman School of Medicine (PSM) - calculations completed under a minute (for some cases) and within minutes have been achieved. We demonstrate results within a 5% error of the analytic solution for multiple detectors in the phantom. PEDSy-MC is accompanied by a dose-cavity visualization tool that allows real-time inspection of dose values of the treated cavity in 2D and 3D, which will be expanded to ongoing clinical trials at PSM. PSM has developed a technology to measure 8-detectors in a pleural cavity phantom using Photofrin-mediated PDT that has been used during validation.

Computational Optimization of Irradiance and Fluence for Interstitial Photodynamic Therapy Treatment of Patients with Malignant Central Airway Obstruction.

There are no effective treatments for patients with extrinsic malignant central airway obstruction (MCAO). In a recent clinical study, we demonstrated that interstitial photodynamic therapy (I-PDT) is a safe and potentially effective treatment for patients with extrinsic MCAO. In previous preclinical studies, we reported that a minimum light irradiance and fluence should be maintained within a significant volume of the target tumor to obtain an effective PDT response. In this paper, we present a computational approach to personalized treatment planning of light delivery in I-PDT that simultaneously optimizes the delivered irradiance and fluence using finite element method (FEM) solvers of either Comsol Multiphysics® or Dosie™ for light propagation. The FEM simulations were validated with light dosimetry measurements in a solid phantom with tissue-like optical properties. The agreement between the treatment plans generated by two FEMs was tested using typical imaging data from four patients with extrinsic MCAO treated with I-PDT. The concordance correlation coefficient (CCC) and its 95% confidence interval (95% CI) were used to test the agreement between the simulation results and measurements, and between the two FEMs treatment plans. Dosie with CCC = 0.994 (95% CI, 0.953-0.996) and Comsol with CCC = 0.999 (95% CI, 0.985-0.999) showed excellent agreement with light measurements in the phantom. The CCC analysis showed very good agreement between Comsol and Dosie treatment plans for irradiance (95% CI, CCC: 0.996-0.999) and fluence (95% CI, CCC: 0.916-0.987) in using patients' data. In previous preclinical work, we demonstrated that effective I-PDT is associated with a computed light dose of ≥45 J/cm2 when the irradiance is ≥8.6 mW/cm2 (i.e., the effective rate-based light dose). In this paper, we show how to use Comsol and Dosie packages to optimize rate-based light dose, and we present Dosie's newly developed domination sub-maps method to improve the planning of the delivery of the effective rate-based light dose. We conclude that image-based treatment planning using Comsol or Dosie FEM-solvers is a valid approach to guide the light dosimetry in I-PDT of patients with MCAO.

Optimal Light Dose for hEGFR-Targeted Near-Infrared Photoimmunotherapy.

Near-infrared photoimmunotherapy (NIR-PIT) is a newly developed cancer therapy that targets cancer cells using a monoclonal antibody-photon absorber conjugate (APC) that is bound to the target cell surface. Subsequent application of low levels of NIR light results in immediate cancer cell death. The anti-tumor effect of NIR-PIT in immunocompromised mice depends on immediate cancer cell death; therefore, the efficacy increases in a light-dose-dependent manner. However, NIR-PIT also induces a strong anti-tumor immune activation in immunocompetent mice that begins soon after therapy. Thus, it may be possible to reduce the light dose, which might otherwise cause local edema while maintaining therapeutic efficacy. In this study, we determined the optimal dose of NIR light in NIR-PIT based on a comparison of the therapeutic and adverse effects. Either one of two monoclonal antibodies (mAbs) against human epidermal growth factor receptor (hEGFR), Cetuximab or Panitumumab, were conjugated with a photo-absorbing chemical, IRDye700DX (IR700), and then injected in hEGFR-expressing mEERL (mEERL-hEGFR) tumor-bearing C57BL/6 immunocompetent mice or A431-GFP-luc tumor-bearing athymic immunocompromised mice. NIR light was varied between 0 to 100 J/cm2 one day after administration of APC. In an immunocompromised mouse model, tumor growth was inhibited in a light-dose-dependent manner, yet extensive local edema and weight loss were observed at 100 J/cm2. On the other hand, in an immunocompetent mouse model using the mEERL-hEGFR cell line, maximal tumor response was achieved at 50 J/cm2, with a commensurate decrease in local edema. In this study, we show that a relatively low dose of NIR light is sufficient in an immunocompetent mouse model and avoids side effects seen with higher light doses required in immunocompetent mice. Thus, light dosing can be optimized in NIR-PIT based on the expected immune response.

An Alternating Irradiation Strategy-Driven Combination Therapy of PDT and RNAi for Highly Efficient Inhibition of Tumor Growth and Metastasis.

Hypoxia and hypoxia induced overexpression of vascular endothelial growth factor (VEGF) not only seriously affects the treatment effects of photodynamic therapy (PDT) but also promotes tumor metastasis. Herein, an alternating irradiation strategy (referred to as alternate use of low/high dose of light [ALHDL] irradiation)-driven combination therapy of PDT and RNA interference (RNAi) is developed to synergistically inhibit tumor growth and metastasis. A cationic amphipathic peptide (ALS) served as a carrier in the co-delivery system of photochlor (HPPH) and siVEGF (ALSH/siVEGF). At the beginning of ALHDL-driven ALSH/siVEGF treatment, short-term LDL irradiation can facilitate the tumor penetration, cellular uptake, and endosome escape of ALSH/siVEGF. Moreover, accompanied by HDL-mediated rapid cell apoptosis and LDL-mediated efficient VEGF silencing, the joint use of PDT and RNAi achieved remarkable antitumor effects both in vitro and in vivo. Importantly, benefited from the excellent performance of ALHDL in slowing the rapid deterioration of the anoxic environment of tumors, and ALSH/siVEGF treatment-mediated highly improved VEGF silencing efficacy and inhibitory effect on angiogenesis, the liver and lung metastases of HeLa cells have been successfully suppressed. Together, this study clearly indicates that ALHDL-driven combination therapy of PDT and RNAi is a highly effective modality for inhibition of tumor growth and metastasis.

Seasonal Efficiency of Supplemental LED Lighting on Growth and Photomorphogenesis of Sweet Basil.

For decisions on supplemental lighting a quantitative knowledge of the plants' responses to light under varying conditions is fundamental. In this study, we developed light dose-response curves of growth and morphological traits for Ocimum basilicum L. and examined the effects of light color (blue, red, and white plus far-red) and natural environment (season) on these curves. Four greenhouse experiments were conducted throughout the year to determine the efficiencies of the light regimes on growth and their effects on plant morphology. A special aspect was the photosynthetic efficiency of far-red light. Linear and monomolecular relationships were found for the relationships between plant traits and supplemental light dose. Traits related to biomass productivity increased linearly with light dose whereas some morphological characters showed a saturation behavior. Red light and white plus far-red light were more efficient in plant dry weight production than blue light, and the plants adapted differently to the light qualities: higher biomass under red light was related to a plant architecture more favorable for light capture, i.e., taller plants and bigger leaves. White plus far-red light, on the other hand, increased leaf mass per area (LMA) and light use efficiency (LUE). Blue light resulted in lowest plant light interception and LUE. Considering photosynthetic effects of near-infrared light (PPFD800, 400-800 nm) instead of photosynthetic photon flux density (PPFD700, 400-700 nm) led to strongly reduced efficiencies. Traits related to photosynthesis such as dry weight, LMA and LUE were particularly affected by PPFD800. There were no interactions between the efficiencies of the different light colors and the seasons. Efficiencies of all light regimes were significantly lower during summer compared to spring and winter. Higher dry weight production during summer compared to winter and spring were a consequence of increased light interception rather than changes in LUE. The observed differences in seasonal efficiencies were directly linked to the amount of natural light present as indicated by changes in the ratio of supplemental to natural light.

Light dose is a limiting factor to maintain cell viability in fluorescence microscopy and single molecule detection.

A test system for cell viability based on colony formation has been established and applied to high resolution fluorescence microscopy and single molecule detection. Living cells were irradiated either by epi-illumination or by total internal reflection (TIR) of a laser beam, and light doses where at least 90% of irradiated cells survived were determined. These light doses were in the range of a few J/cm(2) up to about 200 J/cm(2) depending on the wavelength of illumination as well as on the presence or absence of a fluorescent dye (e.g., the membrane marker laurdan). In general, cells were less sensitive to TIR than to epi-illumination. However, comparably high light doses needed for repetitive excitation of single molecules limit the application of super-resolution microscopy to living cells.

Sulfonated hydroxyaluminum phthalocyanine-biogenic Au/Ag alloy nanoparticles mixtures for effective photo-eradication of Candida albicans.

In response to the increasingly widespread resistance of fungi to traditional treatment, we have reported successful photodynamic inactivation of Candida albicans planktonic cells using di-(AlPcS2) and trisulfonated (AlPcS3) hydroxyaluminum phthalocyanines in combination with Au/Ag alloy nanoparticles synthesized by the cell-free filtrate of Trichoderma koningii. These nanostructures with Au:Ag molar ratios 2:1, 1:1 and 1:2 have individual plasmonic band at 513-515 nm, 505-509 nm and 486-489 nm, respectively. XPS analysis of the ratio of gold to silver on the surface of these alloys indicated that Au and Ag formed a bimetallic system, wherein Au was coated with Ag. The XRD pattern revealed the angles at 38.2, 44.5, 64.9 and 78.0°. TEM analysis indicated that the average diameter of the synthesized alloys was 9 ± 3 nm, 8 ± 3 nm and 16 ± 3 nm for structures with Au:Ag molar ratios 1:1, 1:2 and 2:1, respectively. The FTIR band absorption, SEM-EDS analysis and basic elemental composition obtained by XPS confirmed that these nanostructures are stabilized by protein(s). Diode laser with the peak-power wavelength ʎ = 650 nm (output power of 40 mW; power density of 105 mW cm-2) was used as a light source. The mixture of AlPcS2+Au/Ag-NPs (Au:Ag = 2:1) can be considered as an effective photosensitizer, because eradication of C. albicans, as required by the American Society of Microbiology (99.9 %), was achieved at a low dose of light of 31.5 J cm-2. It was postulated that this low dose of light applied to the photo-induced fungicidal effect may be painless for potential patients.

Modeling PpIX effective light fluence at depths into the skin for PDT dose comparison.

BACKGROUND: Daylight-activated PDT has seen increased support in recent years as a treatment method for actinic keratosis and other non-melanoma skin cancers. The inherent variability observed in broad-spectrum light used in this methodology makes it difficult to plan and monitor light dose, or compare to lamp light doses. METHODS: The present study expands on the commonly used PpIX-weighted effective surface irradiance metric by introducing a Monte Carlo method for estimating effective fluence rates into depths of the skin. The fluence rates are compared between multiple broadband and narrowband sources that have been reported in previous studies, and an effective total fluence for various treatment times is reported. A dynamic estimate of PpIX concentration produced during pro-drug incubation and treatment is used with the fluence estimates to calculate a photodynamic dose. RESULTS: Even when there is up to a 5x reduction between the effective surface irradiance of the broadband light sources, the effective fluence below 250 µm depth is predicted to be relatively equivalent. An effective threshold fluence value (0. 70Jeff/cm2) is introduced based on a meta-analysis of previously published ALA-PpIX induced cell death. This was combined with a threshold PpIX concentration (50 nM) to define a threshold photodynamic dose of 0.035 u M Jeff/cm2. CONCLUSIONS: The threshold was used to generate lookup tables to prescribe minimal treatment times to achieve depth-dependent cytotoxic effect based on incubation times and irradiance values for each light source.

A quality assurance program for clinical PDT.

Successful outcome of Photodynamic therapy (PDT) depends on accurate delivery of prescribed light dose. A quality assurance program is necessary to ensure that light dosimetry is correctly measured. We have instituted a QA program that include examination of long term calibration uncertainty of isotropic detectors for light fluence rate, power meter head intercomparison for laser power, stability of the light-emitting diode (LED) light source integrating sphere as a light fluence standard, laser output and calibration of in-vivo reflective fluorescence and absorption spectrometers. We examined the long term calibration uncertainty of isotropic detector sensitivity, defined as fluence rate per voltage. We calibrate the detector using the known calibrated light fluence rate of the LED light source built into an internally baffled 4″ integrating sphere. LED light sources were examined using a 1mm diameter isotropic detector calibrated in a collimated beam. Wavelengths varying from 632nm to 690nm were used. The internal LED method gives an overall calibration accuracy of ±4%. Intercomparison among power meters was performed to determine the consistency of laser power and light fluence rate measured among different power meters. Power and fluence readings were measured and compared among detectors. A comparison of power and fluence reading among several power heads shows long term consistency for power and light fluence rate calibration to within 3% regardless of wavelength. The standard LED light source is used to calibrate the transmission difference between different channels for the diffuse reflective absorption and fluorescence contact probe as well as isotropic detectors used in PDT dose dosimeter.

Assessment of the actual light dose in photodynamic therapy.

Photodynamic therapy (PDT) initiates with the absorption of light, which depend on the spectral overlap between the light source emission and the photosensitizer absorption, resulting in the number of photons absorbed, the key parameter starting PDT processes. Most papers report light doses regardless if the light is only partially absorbed or shifted relatively to the absorption peak, misleading the actual light dose value and not allowing quantitative comparisons between photosensitizers and light sources. In this manuscript a method is presented to calculate the actual light dose delivered by any light source for a given photosensitizer. This method allows comparing light doses delivered for any combination of light source (broad or narrow band or daylight) and photosensitizer.