Macroscopic singlet oxygen modeling for dosimetry of Photofrin-mediated photodynamic therapy: an in-vivo study

Computational modelling of the therapeutic outputs of photodynamic therapy on spheroid-on-chip models

Photodynamic therapy (PDT) is a medical radio chemotherapeutic method that uses light, photosensitizing agents, and oxygen to produce cytotoxic compounds, which eliminate malignant cells. Recently, Microfluidic systems have been used to analyse photosensitizers (PSs) due to their potential to replicate in vivo environments. While prior studies have established a strong correlation between reacted singlet oxygen concentration and PDT-induced cellular death, the effects that the ambient fluid flow might have on the concentration of oxygen and PS have been disregarded in many, which limits the reliability of the results. Herein, we coupled the transport of oxygen and PS throughout the ambient medium and within the spheroidal multicellular aggregate to initially study the profiles of oxygen and PS concentration alongside PDT-induced cellular death throughout the spheroid before and after radiation. The attained results indicate that the PDT-induced cellular death initiates on the surface of the spheroids and subsequently spreads to the neighbouring regions, which is in great accordance with experimental results. Afterward, the effects that drug-light interval (DLI), fluence rate, PS composition, microchannel height, and inlet flow rate have on the therapeutic outcomes are studied. The findings show that adequate DLI is critical to ensure uniform distribution of PS throughout the medium, and a value of 5 h was found to be sufficient. The composition of PS is critical, as ALA-PpIX induces earlier cell death but accelerates oxygen consumption, especially in the outer layers, depriving the inner layers of oxygen necessary for PDT, which in turn disrupts and prolongs the exposure time compared to mTHPC and Photofrin. Despite the fluence rate directly influencing the singlet oxygen generation rate, increasing the fluence rate by 189 mW/cm2 would not significantly benefit us. Microwell height and inlet flow rate involve competing phenomena-increasing height or decreasing flow reduces oxygen supply and increases PS "washout" and its concentration.

Clinical PDT dose dosimetry for pleural Photofrin-mediated photodynamic therapy

Significance

Photodynamic therapy (PDT) is an established cancer treatment utilizing light-activated photosensitizers (PS). Effective treatment hinges on the PDT dose-dependent on PS concentration and light fluence-delivered over time. We introduce an innovative eight-channel PDT dose dosimetry system capable of concurrently measuring light fluence and PS concentration during treatment.

Aim

We aim to develop and evaluate an eight-channel PDT dose dosimetry system for simultaneous measurement of light fluence and PS concentration. By addressing uncertainties due to tissue variations, the system enhances accurate PDT dosimetry for improved treatment outcomes.

Approach

The study positions eight isotropic detectors strategically within the pleural cavity before PDT. These detectors are linked to bifurcated fibers, distributing signals to both a photodiode and a spectrometer. Calibration techniques are applied to counter tissue-related variations and improve measurement accuracy. The fluorescence signal is normalized using the measured light fluence, compensating for variations in tissue properties. Measurements were taken in 78 sites in the pleural cavities of 20 patients.

Results

Observations reveal minimal Photofrin concentration variation during PDT at each site, juxtaposed with significant intra- and inter-patient heterogeneities. Across 78 treated sites in 20 patients, the average Photofrin concentration for all 78 sites is 4.98    μ M , with a median concentration of 4.47    μ M . The average PDT dose for all 78 sites is 493.17    μ MJ / cm 2 , with a median dose of 442.79    μ MJ / cm 2 . A significant variation in PDT doses is observed, with a maximum difference of 3.1 times among all sites within one patient and a maximum difference of 9.8 times across all patients.

Conclusions

The introduced eight-channel PDT dose dosimetry system serves as a valuable real-time monitoring tool for light fluence and PS concentration during PDT. Its ability to mitigate uncertainties arising from tissue properties enhances dosimetry accuracy, thus optimizing treatment outcomes and bolstering the effectiveness of PDT in cancer therapy.

Fractionated Photofrin-Mediated Photodynamic Therapy Significantly Improves Long-Term Survival

This study investigates the effect of fractionated (two-part) PDT on the long-term local control rate (LCR) using the concentration of reactive oxygen species ([ROS]rx) as a dosimetry quantity. Groups with different fractionation schemes are examined, including a 2 h interval between light delivery sessions to cumulative fluences of 135, 180, and 225 J/cm2. While the total treatment time remains constant within each group, the division of treatment time between the first and second fractionations are explored to assess the impact on long-term survival at 90 days. In all preclinical studies, Photofrin is intravenously administered to mice at a concentration of 5 mg/kg, with an incubation period between 18 and 24 h before the first light delivery session. Fluence rate is fixed at 75 mW/cm2. Treatment ensues via a collimated laser beam, 1 cm in diameter, emitting light at 630 nm. Dosimetric quantities are assessed for all groups along with long-term (90 days) treatment outcomes. This study demonstrated a significant improvement in long-term survival after fractionated treatment schemes compared to single-fraction treatment, with the optimal 90-day survival increasing to 63%, 86%, and 100% vs. 20%, 25%, and 50%, respectively, for the three cumulative fluences. The threshold [ROS]rx for the optimal scheme of fractionated Photofrin-mediated PDT, set at 0.78 mM, is significantly lower than that for the single-fraction PDT, at 1.08 mM.

High Sensitivity Singlet Oxygen Luminescence Sensor Using Computational Spectroscopy and Solid-State Detector

This paper presents a technique for high sensitivity measurement of singlet oxygen luminescence generated during photodynamic therapy (PDT) and ultraviolet (UV) irradiation on skin. The high measurement sensitivity is achieved by using a computational spectroscopy (CS) approach that provides improved photon detection efficiency compared to spectral filtering methodology. A solid-state InGaAs photodiode is used as the CS detector, which significantly reduces system cost and improves robustness compared to photomultiplier tubes. The spectral resolution enables high-accuracy determination and subtraction of photosensitizer fluorescence baseline without the need for time-gating. This allows for high sensitivity detection of singlet oxygen luminescence emission generated by continuous wave light sources, such as solar simulator sources and those commonly used in PDT clinics. The value of the technology is demonstrated during in vivo and ex vivo experiments that show the correlation of measured singlet oxygen with PDT treatment efficacy and the illumination intensity on the skin. These results demonstrate the potential use of the technology as a dosimeter to guide PDT treatment and as an analytical tool supporting the development of improved sunscreen products for skin cancer prevention.

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.

Multispectral singlet oxygen luminescent dosimetry (MSOLD) for Photofrin-mediated Photodynamic Therapy

Direct detection of singlet-state oxygen ([1O2]) constitutes the holy grail dosimetric method for type II PDT, a goal that can be quantified using multispectral singlet oxygen dosimetry (MSOLD). However, the short lifetime and extremely weak nature of the singlet oxygen signal produced has given rise to a need to improve MSOLD signal-to-noise ratio. This study examines methods for optimizing MSOLD signal acquisition, specifically employing an orthogonal arrangement between detection and PDT treatment light, consisting of two fiber optics - connected to a 632-nm laser and an InGaAs detector respectively. Light collected by the InGaAs detector is then passed through a filter wheel, where spectral emission measurements are taken at 1200 nm, 1240 nm, 1250 nm, 1270 nm, and 1300 nm. The data, after fitting to the fluorescence background and a gaussian-fit for the singlet oxygen peak, is established for the background-subtracted singlet oxygen emission signal. The MSOLD signal is then compared with the singlet oxygen explicit dosimetry (SOED) results, based on direct measurements of in-vivo light fluence (rate), in-vivo Photofrin concentration, and tissue oxygenation concentration. This study focuses on validating the sensitivity and minimum detectability of MSOLD signal in various in-vitro conditions. Finally, the MSOLD device will be tested in Photofrin-mediated PDT for mice bearing Radiation-Induced Fibrosarcoma (RIF) tumors.

Mathematical modelling for antimicrobial photodynamic therapy mediated by 5-aminolaevulinic acid: An in vitro study

BACKGROUND

Antimicrobial photodynamic therapy (aPDT) using aminolaevulinic acid (ALA) is a promising alternative to antibiotic therapy. ALA administration induces protoporphyrin IX (PpIX) accumulation in bacteria, and light excitation of the accumulated PpIX generates singlet oxygen to bacterial toxicity. Several factors, including drug administration and light irradiation conditions, contribute to the antibiotic effect. Such multiple parameters should be determined moderately for effective aPDT in clinical practice.

METHODS

A mathematical model to predict bacterial dynamics in ALA-aPDT following clinical conditions was constructed. Applying a pharmacokineticspharmacodynamics (PK-PD) approach, which is widely used in antimicrobial drug evaluation, viable bacteria count by defining the bactericidal rate as the concentration of singlet oxygen produced when PpIX in bacteria is irradiated by light.

RESULTS

The in vitro experimental results of ALA-aPDT for Pseudomonas aeruginosa demonstrated the PK-PD model validity. The killing rate has an upper limit, and the lower power density for a long irradiation time can suppress the viable bacteria number when the light dosages are the same.

CONCLUSIONS

This study proposed a model of bacterial viability change in ALA-aPDT based on the PK-PD model and confirmed, by in vitro experiments using PA, that the variation of bacterial viability with light-sensitive substance concentration and light irradiation power densities could be expressed. Further validation of the PK-PD model with other gram negative and gram positive strains will be needed.

Real-time PDT Dose Dosimetry for Pleural Photodynamic Therapy

PDT dose is the product of the photosensitizer concentration and the light fluence in the target tissue. For improved dosimetry during plural photodynamic therapy (PDT), an eight-channel PDT dose dosimeter was developed to measure both the light fluence and the photosensitizer concentration simultaneously from eight different sites in the pleural cavity during PDT. An isotropic detector with bifurcated fibers was used for each channel to ensure detected light was split equally to the photodiode and spectrometer. The light fluence rate distribution is monitored using an IR navigation system. The navigation system allows 2D light fluence mapping throughout the whole pleural cavity rather than just the selected points. The fluorescence signal is normalized by the light fluence measured at treatment wavelength. We have shown that the absolute photosensitizer concentration can be obtained by applying optical properties correction and linear spectral fitting to the measured fluorescence data. The detection limit and the optical property correction factor of each channel were determined and validated using tissue-simulating phantoms with known varying concentration of Photofrin. Tissue optical properties are determined using an absorption spectroscopy probe immediately before PDT at the same sites. The combination of 8-channel PDT dosimeter system and IR navigation system, which can calculate light fluence rate in the pleural cavity in real-time, providing a mean to determine the distribution of PDT dose on the entire pleural cavity to investigate the heterogeneity of PDT dose on the pleural cavity.

High optical-throughput spectroscopic singlet oxygen and photosensitizer luminescence dosimeter for monitoring of photodynamic therapy

We report a high light-throughput spectroscopic dosimeter system that is able to noninvasively measure luminescence signals of singlet oxygen (¹ O₂ ) produced during photodynamic therapy (PDT) using a CW (continuous wave) light source. The system is based on a compact, fiber-coupled, high collection efficiency spectrometer (>50% transmittance) designed to maximize optical throughput but with sufficient spectral resolution (~7 nm). This is adequate to detect ¹ O₂ phosphorescence in the presence of strong luminescence background in vivo. This system provides simultaneous acquisition of multiple spectral data points, allowing for more accurate determination of luminescence baseline via spectral fitting and thus the extraction of ¹ O₂ phosphorescence signal based solely on spectroscopic decomposition, without the need for time-gating. Simultaneous collection of photons at different wavelengths improves the quantum efficiency of the system when compared to sequential spectral measurements such as filter-wheel or tunable-filter based systems. A prototype system was tested during in vivo PDT tumor regression experiments using benzoporphyrin derivative (BPD) photosensitizer. It was found that the treatment efficacy (tumor growth inhibition rate) correlated more strongly with ¹ O₂ phosphorescence than with PS fluorescence. These results indicate that this high photon-collection efficiency spectrometer instrument may offer a viable option for real-time ¹ O₂ dosimetry during PDT treatment using CW light.

Recent progress in sono-photodynamic cancer therapy: From developed new sensitizers to nanotechnology-based efficacy-enhancing strategies

Many sensitizers have not only photodynamic effects, but also sonodynamic effects. Therefore, the combination of sonodynamic therapy (SDT) and photodynamic therapy (PDT) using sensitizers for sono-photodynamic therapy (SPDT) provides alternative opportunities for clinical cancer therapy. Although significant advances have been made in synthesizing new sensitizers for SPDT, few of them are successfully applied in clinical settings. The anti-tumor effects of the sensitizers are restricted by the lack of tumor-targeting specificity, incapability in deep intratumoral delivery, and the deteriorating tumor microenvironment. The application of nanotechnology-based drug delivery systems (NDDSs) can solve the above shortcomings, thereby improving the SPDT efficacy. This review summarizes various sensitizers as sono/photosensitizers that can be further used in SPDT, and describes different strategies for enhancing tumor treatment by NDDSs, such as overcoming biological barriers, improving tumor-targeted delivery and intratumoral delivery, providing stimuli-responsive controlled-release characteristics, stimulating anti-tumor immunity, increasing oxygen supply, employing different therapeutic modalities, and combining diagnosis and treatment. The challenges and prospects for further development of intelligent sensitizers and translational NDDSs for SPDT are also discussed.

Can Cerenkov Light Really Induce an Effective Photodynamic Therapy?

Photodynamic therapy (PDT) is a promising therapeutic strategy for cancers where surgery and radiotherapy cannot be effective. PDT relies on the photoactivation of photosensitizers, most of the time by lasers to produced reactive oxygen species and notably singlet oxygen. The major drawback of this strategy is the weak light penetration in the tissues. To overcome this issue, recent studies proposed to generate visible light in situ with radioactive isotopes emitting charged particles able to produce Cerenkov radiation. In vitro and preclinical results are appealing, but the existence of a true, lethal phototherapeutic effect is still controversial. In this article, we have reviewed previous original works dealing with Cerenkov-induced PDT (CR-PDT). Moreover, we propose a simple analytical equation resolution to demonstrate that Cerenkov light can potentially generate a photo-therapeutic effect, although most of the Cerenkov photons are emitted in the UV-B and UV-C domains. We suggest that CR-PDT and direct UV-tissue interaction act synergistically to yield the therapeutic effect observed in the literature. Moreover, adding a nanoscintillator in the photosensitizer vicinity would increase the PDT efficacy, as it will convert Cerenkov UV photons to light absorbed by the photosensitizer.

Reactive oxygen species explicit dosimetry to predict local tumor growth for Photofrin-mediated photodynamic therapy

Although photodynamic therapy (PDT) is an established modality for cancer treatment, current dosimetric quantities, such as light fluence and PDT dose, do not account for the differences in PDT oxygen consumption for different fluence rates (ϕ). A macroscopic model was adopted to calculate reactive oxygen species concentration ([ROS]_rx) to predict Photofrin-PDT outcome in mice bearing radiation-induced fibrosarcoma (RIF) tumors. Singlet oxygen is the primary cytotoxic species for ROS, which is responsible for cell death in type II PDT, although other type I ROS is included in the parameters used in our model. Using a combination of fluences (50-250 J∕cm²) and ϕ (75 or 150 mW∕cm²), tumor regrowth rate, k, was determined for each condition by fitting the tumor volume versus time to V₀ *exp(k*t). Treatment was delivered with a collimated laser beam of 1 cm diameter at 630 nm. Explicit dosimetry of light fluence rate on tissue surface, tissue oxygen concentration, tissue optical properties, and Photofrin concentration were performed. Light fluence rate at 3 mm depth (ϕ _3mm) was determined for the treatment volume based on Monte-Carlo simulations and measured tissue optical properties. Initial tissue oxygenation [³ O ₂]₀ was measured by an Oxylite oxygen probe before PDT and used to calculate [ROS]_rx,calc. This value was compared to [ROS]_rx,meas as calculated with the entire tissue oxygen spectrum [³ O ₂](t), measured over the duration of light delivery for PDT. Cure index, CI = 1-k/k_ctr , for tumor growth up to 14 days after PDT was predicted by four dose metrics: light fluence, PDT dose, and [ROS]_rx,calc, and [ROS]_rx,meas. PDT dose was defined as the product of the time-integral of photosensitizer concentration and ϕ at a 3 mm tumor depth. These studies show that [ROS]_rx,meas best correlates with CI and is an effective dosimetric quantity that can predict treatment outcome.

In vivo Spectroscopic Evaluation of the Intraperitoneal Cavity in Canines

As part of a preclinical trial for the treatment of peritoneal carcinomatosis (PC) with photodynamic therapy (PDT), we have assessed changes in optical properties, tissue oxygenation and drug concentration as a result of benzoporphyrin derivative (BPD)-mediated PDT using diffuse reflectance and fluorescence measurements. PDT can effectively treat superficial disease spread, but treatment efficacy is influenced by physical properties of the treated tissue which can change over the treatment time. In this study, healthy canines were given BPD and irradiated with 690 nm light during a partial bowel resection, and spectroscopic and fluorescence measurements were made using an in-house built spectroscopic probe. Hemoglobin concentration, oxygenation and optical properties were determined to be highly heterogeneous between canines and at different anatomical locations within the same subject, so further development of PDT dosimetry systems will need to address this patient and location-specific dose optimization. Compared to other photosensitizers, we found no apparent BPD photobleaching after PDT.

Multispectral singlet oxygen and photosensitizer luminescence dosimeter for continuous photodynamic therapy dose assessment during treatment

SIGNIFICANCE

Photodynamic therapy (PDT) involves complex light-drug-pathophysiology interactions that can be affected by multiple parameters and often leads to large variations in treatment outcome from patient to patient. Direct PDT dosimetry technologies have been sought to optimize the control variables (e.g., light dose, drug administration, tissue oxygenation, and patient conditioning) for best patient outcomes. In comparison, singlet oxygen (O21) dosimetry has been tested in various forms to provide an accurate and perhaps comprehensive prediction of the treatment efficacy.

AIM

We discuss an advanced version of this approach provided by a noninvasive, continuous wave dosimeter that can measure near-infrared spectrally resolved luminescence of both photosensitizer (PS) and O21 generated during PDT cancer treatment.

APPROACH

This dosimetry technology uses an amplified, high quantum efficiency InGaAs detector with spectroscopic decomposition during the light treatment to continuously extract the maximum signal of O21 phosphorescence while suppressing the strong PS luminescence background by spectrally fitting the data points across nine narrow band wavelengths. O21 and PS luminescence signals were measured in vivo in FaDu xenograft tumors grown in mice during PDT treatment using Verteporfin as the PS and a continuous laser treatment at 690 nm wavelength.

RESULTS

A cohort of 19 mice was used and observations indicate that the tumor growth rate inhibition showed a stronger correlation with O21 than with just the PS signal.

CONCLUSIONS

These results suggest that O21 measurement may be a more direct dosimeter of PDT damage, and it has potential value as a definitive diagnostic for PDT treatment, especially with spectral separation of the background luminescence and online estimation of the PS concentration.

1O2 determined from the measured PDT dose and 3O2 predicts long-term response to Photofrin-mediated PDT

Photodynamic therapy (PDT) that employs the photochemical interaction of light, photosensitizer and oxygen is an established modality for the treatment of cancer. However, dosimetry for PDT is becoming increasingly complex due to the heterogeneous photosensitizer uptake by the tumor, and complicated relationship between the tissue oxygenation ([³O₂]), interstitial light distribution, photosensitizer photobleaching and PDT effect. As a result, experts argue that the failure to realize PDT's true potential is, at least partly due to the complexity of the dosimetry problem. In this study, we examine the efficacy of singlet oxygen explicit dosimetry (SOED) based on the measurements of the interstitial light fluence rate distribution, changes of [³O₂] and photosensitizer concentration during Photofrin-mediated PDT to predict long-term control rates of radiation-induced fibrosarcoma tumors. We further show how variation in tissue [³O₂] between animals induces variation in the treatment response for the same PDT protocol. PDT was performed with 5 mg kg^-1 Photofrin (a drug-light interval of 24 h), in-air fluence rates (ϕ _air) of 50 and 75 mW cm^-2 and in-air fluences from 225 to 540 J cm^-2. The tumor regrowth was tracked for 90 d after the treatment and Kaplan-Meier analyses for local control rate were performed based on a tumor volume  ⩽100 mm³ for the two dosimetry quantities of PDT dose and SOED. Based on the results, SOED allowed for reduced subject variation and improved treatment evaluation as compared to the PDT dose.

Reactive oxygen species explicit dosimetry to predict tumor growth for benzoporphyrin derivative-mediated vascular photodynamic therapy

Photodynamic therapy (PDT) is a well-established treatment modality for cancer and other malignant diseases; however, quantities such as light fluence and PDT dose do not fully account for all of the dynamic interactions between the key components involved. In particular, fluence rate (ϕ) effects, which impact the photochemical oxygen consumption rate, are not accounted for. In this preclinical study, reacted reactive oxygen species ([ROS]_rx) was investigated as a dosimetric quantity for PDT outcome. The ability of [ROS]_rx to predict the cure index (CI) of tumor growth, CI  =  1  -  k  /  k_ctr, where k and k_ctr are the growth rate of tumor under PDT study and the control tumor without PDT, respectively, for benzoporphyrin derivative (BPD)-mediated PDT, was examined. Mice bearing radiation-induced fibrosarcoma (RIF) tumors were treated with different in-air fluences (Φ  =  22.5 to 166.7  J  /  cm²) and in-air fluence rates (ϕ_air  =  75 to 250   mW  /  cm²) with a BPD dose of 1  mg  /  kg and a drug-light interval (DLI) of 15 min. Treatment was delivered with a collimated laser beam of 1-cm-diameter at 690 nm. Explicit measurements of in-air light fluence rate, tissue oxygen concentration, and BPD concentration were used to calculate for [ROS]_rx. Light fluence rate at 3-mm depth (ϕ_3  mm), determined based on Monte-Carlo simulations, was used in the calculation of [ROS]_rx at the base of tumor. CI was used as an endpoint for three dose metrics: light fluence, PDT dose, and [ROS]_rx. PDT dose was defined as the product of the time-integral of photosensitizer concentration and ϕ_3  mm. Preliminary studies show that [ROS]_rx best correlates with CI and is an effective dosimetric quantity that can predict treatment outcome. The threshold dose for [ROS]_rx for vascular BPD-mediated PDT using DLI of 15 min is determined to be 0.26 mM and is about 3.8 times smaller than the corresponding value for conventional BPD-mediated PDT using DLI of 3 h.

Reactive Oxygen Species Explicit Dosimetry for Photofrin-mediated Pleural Photodynamic Therapy

Explicit dosimetry of treatment light fluence and implicit dosimetry of photosensitizer photobleaching are commonly used methods to guide dose delivery during clinical PDT. Tissue oxygen, however, is not routinely monitored intraoperatively even though it is one of the three major components of treatment. Quantitative information about in vivo tissue oxygenation during PDT is desirable, because it enables reactive oxygen species explicit dosimetry (ROSED) for prediction of treatment outcome based on PDT-induced changes in tumor oxygen level. Here, we demonstrate ROSED in a clinical setting, Photofrin-mediated pleural photodynamic therapy, by utilizing tumor blood flow information measured by diffuse correlation spectroscopy (DCS). A DCS contact probe was sutured to the pleural cavity wall after surgical resection of pleural mesothelioma tumor to monitor tissue blood flow (blood flow index) during intraoperative PDT treatment. Isotropic detectors were used to measure treatment light fluence and photosensitizer concentration. Blood-flow-derived tumor oxygen concentration, estimated by applying a preclinically determined conversion factor of 1.5 × 10⁹ μMs cm^-2 to the blood flow index, was used in the ROSED model to calculate the total reacted reactive oxygen species [ROS]rx. Seven patients and 12 different pleural sites were assessed and large inter- and intrapatient heterogeneities in [ROS]rx were observed although an identical light dose of 60 J cm^-2 was prescribed to all patients.

Singlet oxygen model evaluation of interstitial photodynamic therapy with 5-aminolevulinic acid for malignant brain tumor

Interstitial photodynamic therapy (iPDT) with 5-aminolevulinic acid (ALA) is a possible alternative treatment for malignant brain tumors. Further evaluation is, however, required before it can be clinically applied. Computational simulation of the photophysical process in ALA-iPDT can offer a quantitative tool for understanding treatment outcomes, which depend on various variables related to clinical treatment conditions. We propose a clinical simulation method of ALA-iPDT for malignant brain tumors using a singlet oxygen (O1₂) model and O1₂ threshold to induce cell death. In this method, the amount of O1₂ generated is calculated using a photosensitizer photobleaching coefficient and O1₂ quantum yield, which have been measured in several previous studies. Results of the simulation using clinical magnetic resonance imaging data show the need to specify the insertion positions of cylindrical light diffusers and the level of light fluence. Detailed analysis with a numerical brain tumor model demonstrates that ALA-iPDT treatment outcomes depend on combinations of photobleaching and threshold values. These results indicate that individual medical procedures, including pretreatment planning and treatment monitoring, will greatly benefit from simulation of ALA-iPDT outcomes.

Reactive oxygen species explicit dosimetry to predict local tumor control for Photofrin-mediated photodynamic therapy

Although photodynamic therapy (PDT) is an established modality for cancer treatment, current dosimetric quantities, such as light fluence and PDT dose, do not account for the differences in PDT oxygen consumption for different fluence rates (ϕ). A macroscopic model was adopted to calculate reactive oxygen species concentration ([ROS]_rx) to predict Photofrin-PDT outcome in mice bearing radiation-induced fibrosarcoma (RIF) tumors. Singlet oxygen is the primary cytotoxic species for ROS, which is responsible for cell death in type II PDT, although other type I ROS is included in the parameters used in our model. Using a combination of fluences (50-250 J/cm²) and ϕ (50 - 150 mW/cm²), tumor regrowth rate, k, was determined for each condition by fitting the tumor volume vs. time to V₀*exp(k*t). Treatment was delivered with a collimated laser beam of 1 cm diameter at 630 nm. Explicit dosimetry of initial tissue oxygen concentration, tissue optical properties, and Photofrin concentration was used to calculate [ROS]_rx,cal. ϕ was determined for the treatment volume based on Monte-Carlo simulations and measured tissue optical properties. Tissue oxygenation is measured using an oxylite oxygen probe to throughout the treatment to calculate the measured [ROS]_rx,mea. Cure index, CI = 1-k/k _ctr , for tumor gowth up to 14 days were determined as an endpoint using five dose metrics: light fluence, PDT dose, and [ROS]_rx,cal, and [ROS]_rx,mea. PDT dose was defined as the product of the time-integral of photosensitizer concentration and ϕ at a 3 mm tumor depth. Preliminary studies show that [ROS]_rx,mea best correlates with CI and is an effective dosimetric quantity that can predict treatment outcome.

Validation of combined Monte Carlo and photokinetic simulations for the outcome correlation analysis of benzoporphyrin derivative-mediated photodynamic therapy on mice

We compare previously reported benzoporphyrin derivative (BPD)-mediated photodynamic therapy (PDT) results for reactive singlet oxygen concentration (also called singlet oxygen dose) on mice with simulations using a computational device, Dosie™, that calculates light transport and photokinetics for PDT in near real-time. The two sets of results are consistent and validate the use of the device in PDT treatment planning to predict BPD-mediated PDT outcomes in mice animal studies based on singlet oxygen dose, which showed a much better correlation with the cure index than the conventional light dose.

Reactive oxygen species explicit dosimetry to predict tumor growth for BPD-mediated vascular photodynamic therapy

Photodynamic therapy (PDT) is a well-established treatment modality for cancer and other malignant diseases; however, quantities such as light fluence, and PDT dose do not fully account for all of the dynamic interactions between the key components involved. In particular, fluence rate (ϕ) effects are not accounted for, which has a large effect on the oxygen consumption rate. In this preclinical study, reacted reactive oxygen species ([ROS]_rx) was investigated as a dosimetric quantity for PDT outcome. We studied the ability of [ROS]_rx to predict the cure index (CI) after PDT of murine tumors; CI = 1 - k/k_ctr, where k and k_ctr are the growth rate of PDT-treated and control(untreated) tumor, respectively. Mice bearing radiation induced fibrosarcoma (RIF) tumors were treated with BPD-mediated PDT at different in-air fluences (22.5, 40, 45, 50, 70 and 100 J/cm²) and in-air ϕ (75 and 150 mW/cm²) with a BPD dose of 1 mg/kg and a drug-light interval of 15 mins. Treatment was delivered with a collimated laser beam of 1 cm diameter at 690 nm. Explicit dosimetry of initial tissue oxygen concentration, tissue optical properties, and BPD concentration was used to calculate [ 1 O 2 ] rx . ϕ was calculated for the treatment volume based on Monte-Carlo simulations and measured tissue optical properties. CI was used as an endpoint for four dose metrics: light fluence, PDT dose, and [ROS]_rx. PDT dose was defined as the product of the time-integral of photosensitizer concentration and ϕ at a 3 mm tumor depth. Preliminary studies show that [ROS]_rx best correlates with CI and is an effective dosimetric quantity that can predict treatment outcome. The threshold dose for [ROS]_rx is determined to be 0.23 mM and is about 4.3 times smaller than the corresponding value for conventional BPD-mediated PDT using DLI of 3 hrs.

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.

PDT dose dosimetry for Photofrin-mediated pleural photodynamic therapy (pPDT)

Photosensitizer fluorescence excited by photodynamic therapy (PDT) treatment light can be used to monitor the in vivo concentration of the photosensitizer and its photobleaching. The temporal integral of the product of in vivo photosensitizer concentration and light fluence is called PDT dose, which is an important dosimetry quantity for PDT. However, the detected photosensitizer fluorescence may be distorted by variations in the absorption and scattering of both excitation and fluorescence light in tissue. Therefore, correction of the measured fluorescence for distortion due to variable optical properties is required for absolute quantification of photosensitizer concentration. In this study, we have developed a four-channel PDT dose dosimetry system to simultaneously acquire light dosimetry and photosensitizer fluorescence data. We measured PDT dose at four sites in the pleural cavity during pleural PDT. We have determined an empirical optical property correction function using Monte Carlo simulations of fluorescence for a range of physiologically relevant tissue optical properties. Parameters of the optical property correction function for Photofrin fluorescence were determined experimentally using tissue-simulating phantoms. In vivo measurements of photosensitizer fluorescence showed negligible photobleaching of Photofrin during the PDT treatment, but large intra- and inter-patient heterogeneities of in vivo Photofrin concentration are observed. PDT doses delivered to 22 sites in the pleural cavity of 8 patients were different by 2.9 times intra-patient and 8.3 times inter-patient.

Investigating the effect of poly-l-lactic acid nanoparticles carrying hypericin on the flow-biased diffusive motion of HeLa cell organelles

OBJECTIVES

In this study, we investigate in human cervical epithelial HeLa cells the intracellular dynamics and the mutual interaction with the organelles of the poly-l-lactic acid nanoparticles (PLLA NPs) carrying the naturally occurring hydrophobic photosensitizer hypericin.

METHODS

Temporal and spatiotemporal image correlation spectroscopy was used for the assessment of the intracellular diffusion and directed motion of the nanocarriers by tracking the hypericin fluorescence. Using image cross-correlation spectroscopy and specific fluorescent labelling of endosomes, lysosomes and mitochondria, the NPs dynamics in association with the cell organelles was studied. Static colocalization experiments were interpreted according to the Manders' overlap coefficient.

KEY FINDINGS

Nanoparticles associate with a small fraction of the whole-organelle population. The organelles moving with NPs exhibit higher directed motion compared to those moving without them. The rate of the directed motion drops substantially after the application of nocodazole. The random component of the organelle motions is not influenced by the NPs.

CONCLUSIONS

Image correlation and cross-correlation spectroscopy are most appropriate to unravel the motion of the PLLA nanocarrier and to demonstrate that the rate of the directed motion of organelles is influenced by their interaction with the nanocarriers. Not all PLLA-hypericin NPs are associated with organelles.

Three-dimensional finite-element based deformable image registration for evaluation of pleural cavity irradiation during photodynamic therapy

PURPOSE

Photodynamic therapy (PDT) is used after surgical resection to treat the microscopic disease for malignant pleural mesothelioma and to increase survival rates. As accurate light delivery is imperative to PDT efficacy, the deformation of the pleural volume during the surgery is studied on its impact on the delivered light fluence. In this study, a three-dimensional finite element-based (3D FEM) deformable image registration is proposed to directly match the volume of lung to the volume of pleural cavity obtained during PDT to have accurate representation of the light fluence accumulated in the lung, heart and liver (organs-at-risk) during treatment.

METHODS

A wand, comprised of a modified endotrachial tube filled with Intralipid and an optical fiber inside the tube, is used to deliver the treatment light. The position of the treatment is tracked using an optical tracking system with an attachment comprised of nine reflective passive markers that are seen by an infrared camera-based navigation system. This information is used to obtain the surface contours of the plural cavity and the cumulative light fluence on every point of the cavity surface that is being treated. The lung, heart, and liver geometry are also reconstructed from a series of computed tomography (CT) scans of the organs acquired in the same patient before and after the surgery. The contours obtained with the optical tracking system and CTs are imported into COMSOL Multiphysics, where the 3D FEM-based deformable image registration is obtained. The delivered fluence values are assigned to the respective positions (x, y, and z) on the optical tracking contour. The optical tracking contour is considered as the reference, and the CT contours are used as the target, which will be deformed. The data from three patients formed the basis for this study.

RESULTS

The physical correspondence between the CT and optical tracking geometries, taken at different times, from different imaging devices was established using the 3D FEM-based image deformable registration. The volume of lung was matched to the volume of pleural cavity and the distribution of light fluence on the surface of the heart, liver and deformed lung volumes was obtained.

CONCLUSION

The method used is appropriate for analyzing problems over complicated domains, such as when the domain changes (as in a solid-state reaction with a moving boundary), when the desired precision varies over the entire domain, or when the solution lacks smoothness. Implementing this method in real-time for clinical applications and in situ monitoring of the under- or over- exposed regions to light during PDT can significantly improve the treatment for mesothelioma.

On the in vivo photochemical rate parameters for PDT reactive oxygen species modeling

Photosensitizer photochemical parameters are crucial data in accurate dosimetry for photodynamic therapy (PDT) based on photochemical modeling. Progress has been made in the last few decades in determining the photochemical properties of commonly used photosensitizers (PS), but mostly in solution or in vitro. Recent developments allow for the estimation of some of these photochemical parameters in vivo. This review will cover the currently available in vivo photochemical properties of photosensitizers as well as the techniques for measuring those parameters. Furthermore, photochemical parameters that are independent of environmental factors or are universal for different photosensitizers will be examined. Most photosensitizers discussed in this review are of the type II (singlet oxygen) photooxidation category, although type I photosensitizers that involve other reactive oxygen species (ROS) will be discussed as well. The compilation of these parameters will be essential for ROS modeling of PDT.

A Comparison of Dose Metrics to Predict Local Tumor Control for Photofrin-mediated Photodynamic Therapy

This preclinical study examines light fluence, photodynamic therapy (PDT) dose and "apparent reacted singlet oxygen," [¹ O₂ ]_rx , to predict local control rate (LCR) for Photofrin-mediated PDT of radiation-induced fibrosarcoma (RIF) tumors. Mice bearing RIF tumors were treated with in-air fluences (50-250 J cm^-2 ) and in-air fluence rates (50-150 mW cm^-2 ) at Photofrin dosages of 5 and 15 mg kg^-1 and a drug-light interval of 24 h using a 630-nm, 1-cm-diameter collimated laser. A macroscopic model was used to calculate [¹ O₂ ]_rx and PDT dose based on in vivo explicit dosimetry of the drug concentration, light fluence and tissue optical properties. PDT dose and [¹ O₂ ]_rx were defined as a temporal integral of drug concentration and fluence rate, and singlet oxygen concentration consumed divided by the singlet oxygen lifetime, respectively. LCR was stratified for different dose metrics for 74 mice (66 + 8 control). Complete tumor control at 14 days was observed for [¹ O₂ ]_rx ≥ 1.1 mm or PDT dose ≥1200 μm J cm^-2 but cannot be predicted with fluence alone. LCR increases with increasing [¹ O₂ ]_rx and PDT dose but is not well correlated with fluence. Comparing dosimetric quantities, [¹ O₂ ]_rx outperformed both PDT dose and fluence in predicting tumor response and correlating with LCR.

Evaluation of singlet oxygen explicit dosimetry for predicting treatment outcomes of benzoporphyrin derivative monoacid ring A-mediated photodynamic therapy

Existing dosimetric quantities do not fully account for the dynamic interactions between the key components of photodynamic therapy (PDT) or the varying PDT oxygen consumption rates for different fluence rates. Using a macroscopic model, reacted singlet oxygen ( [ O 2 1 ] rx ) was calculated and evaluated for its effectiveness as a dosimetric metric for PDT outcome. Mice bearing radiation-induced fibrosarcoma tumors were treated with benzoporphyrin derivative monoacid ring A (BPD) at a drug-light interval of 3 h with various in-air fluences (30 to 350 ?? J / cm 2 ) and in-air fluence rates (50 to 150 ?? mW / cm 2 ). Explicit measurements of BPD concentration and tissue optical properties were performed and used to calculate [ O 2 1 ] rx , photobleaching ratio, and PDT dose. For four mice, in situ measurements of O 2

Interstitial Photodynamic Therapy-A Focused Review

Multiple clinical studies have shown that interstitial photodynamic therapy (I-PDT) is a promising modality in the treatment of locally-advanced cancerous tumors. However, the utilization of I-PDT has been limited to several centers. The objective of this focused review is to highlight the different approaches employed to administer I-PDT with photosensitizers that are either approved or in clinical studies for the treatment of prostate cancer, pancreatic cancer, head and neck cancer, and brain cancer. Our review suggests that I-PDT is a promising treatment in patients with large-volume or thick tumors. Image-based treatment planning and real-time dosimetry are required to optimize and further advance the utilization of I-PDT. In addition, pre- and post-imaging using computed tomography (CT) with contrast may be utilized to assess the response.

A Comparison of Singlet Oxygen Explicit Dosimetry (SOED) and Singlet Oxygen Luminescence Dosimetry (SOLD) for Photofrin-Mediated Photodynamic Therapy

Accurate photodynamic therapy (PDT) dosimetry is critical for the use of PDT in the treatment of malignant and nonmalignant localized diseases. A singlet oxygen explicit dosimetry (SOED) model has been developed for in vivo purposes. It involves the measurement of the key components in PDT-light fluence (rate), photosensitizer concentration, and ground-state oxygen concentration ([³O₂])-to calculate the amount of reacted singlet oxygen ([¹O₂]rx), the main cytotoxic component in type II PDT. Experiments were performed in phantoms with the photosensitizer Photofrin and in solution using phosphorescence-based singlet oxygen luminescence dosimetry (SOLD) to validate the SOED model. Oxygen concentration and photosensitizer photobleaching versus time were measured during PDT, along with direct SOLD measurements of singlet oxygen and triplet state lifetime (τΔ and τt), for various photosensitizer concentrations to determine necessary photophysical parameters. SOLD-determined cumulative [¹O₂]rx was compared to SOED-calculated [¹O₂]rx for various photosensitizer concentrations to show a clear correlation between the two methods. This illustrates that explicit dosimetry can be used when phosphorescence-based dosimetry is not feasible. Using SOED modeling, we have also shown evidence that SOLD-measured [¹O₂]rx using a 523 nm pulsed laser can be used to correlate to singlet oxygen generated by a 630 nm laser during a clinical malignant pleural mesothelioma (MPM) PDT protocol by using a conversion formula.

Analytic function for predicting light fluence rate of circular fields on a semi-infinite turbid medium

Accurate determination of in-vivo light fluence rate is critical for preclinical and clinical studies involving photodynamic therapy (PDT). The light fluence distribution in tissue depends on both the tissue optical properties and the incident field size. This study compares the longitudinal light fluence distribution inside biological tissue in the central axis of circular uniform light field with different radii for a range of in-vivo tissue optical properties (absorption coefficients (µa) between 0.01 and 1 cm-1 and reduced scattering coefficients (µs') between 2 and 40 cm-1). This was done using Monte-Carlo simulations for a semi-infinite turbid medium in an air-tissue interface. The end goal is to develop simple analytical expressions that would fit the results from the Monte Carlo simulation for circular beams with different radii. A 6-parameter model (ϕ/ϕair=(1-b⋅e-λ1d)(C2e-λ2d+C3e-λ3d)) can be used to fit MC simulation. Each of these parameters (b, C2, C3, λ1, λ2, and λ3) is expressed as a function of tissue optical properties and beam radius. These results can then be compared against the existing expressions in the literature for broad beam for analysis in both accuracy and applicable range. The analytical function can be used as rapid guide in PDT to calculate in vivo light fluence distribution for known tissue optical properties.