Preliminary measurements of optical properties in human abscess cavities prior to methylene blue photodynamic therapy

Devices and Methods for Dosimetry of Personalized Photodynamic Therapy of Tumors: A Review on Recent Trends

Significance: Despite the widespread use of photodynamic therapy in clinical practice, there is a lack of personalized methods for assessing the sufficiency of photodynamic exposure on tumors, depending on tissue parameters that change during light irradiation. This can lead to different treatment results. Aim: The objective of this article was to conduct a comprehensive review of devices and methods employed for the implicit dosimetric monitoring of personalized photodynamic therapy for tumors. Methods: The review included 88 peer-reviewed research articles published between January 2010 and April 2024 that employed implicit monitoring methods, such as fluorescence imaging and diffuse reflectance spectroscopy. Additionally, it encompassed computer modeling methods that are most often and successfully used in preclinical and clinical practice to predict treatment outcomes. The Internet search engine Google Scholar and the Scopus database were used to search the literature for relevant articles. Results: The review analyzed and compared the results of 88 peer-reviewed research articles presenting various methods of implicit dosimetry during photodynamic therapy. The most prominent wavelengths for PDT are in the visible and near-infrared spectral range such as 405, 630, 660, and 690 nm. Conclusions: The problem of developing an accurate, reliable, and easily implemented dosimetry method for photodynamic therapy remains a current problem, since determining the effective light dose for a specific tumor is a decisive factor in achieving a positive treatment outcome.

Treatment planning for photodynamic therapy of abscess cavities using patient-specific optical properties measured prior to illumination

Photodynamic therapy (PDT) is an effective antimicrobial therapy that we used to treat human abscess cavities in a Phase 1 clinical trial. This trial included pre-PDT measurements of abscess optical properties, which affect light dose (light fluence) at the abscess wall and PDT response. This study simulated PDT treatment planning for 13 subjects that received optical spectroscopy prior to clinical PDT, to determine the impact of measured optical properties on ability to achieve fluence rate targets in 95% of the abscess wall. Retrospective treatment plans were evaluated for 3 conditions: (1) clinically delivered laser power and assumed, homogeneous optical properties, (2) clinically delivered laser power and measured, homogeneous optical properties, and (3) with patient-specific treatment planning using measured, homogeneous optical properties. Treatment plans modified delivered laser power, intra-cavity Intralipid (scatterer) concentration, and laser fiber type. Using flat-cleaved laser fibers, the proportion of subjects achieving 95% abscess wall coverage decreased significantly relative to assumed optical properties when using measured values for 4 mW cm-2(92% versus 38%,p= 0.01) and 20 mW cm-2(62% versus 15%,p= 0.04) thresholds. When measured optical properties were incorporated into treatment planning, the 4 mW cm-2target was achieved for all cases. After treatment planning, optimal Intralipid concentration across subjects was 0.14 ± 0.09%, whereas 1% was used clinically. Required laser power to achieve the 4 mW cm-2target was significantly correlated with measured abscess wall absorption (ρ= 0.7,p= 0.008), but not abscess surface area (ρ= 0.2,p= 0.53). When using spherical diffuser fibers for illumination, both optimal Intralipid concentration (p= 0.0005) and required laser power (p= 0.0002) decreased compared to flat cleaved fibers. At 0% Intralipid concentration, the 4 mW cm-2target could only be achieved for 69% of subjects for flat-cleaved fibers, compared to 100% for spherical diffusers. Based on large inter-subject variations in optical properties, individualized treatment planning is essential for abscess photodynamic therapy. (Clinical Trial Registration: The parent clinical trial from which these data were acquired is registered on ClinicalTrials.gov as 'Safety and Feasibility Study of Methylene Blue Photodynamic Therapy to Sterilize Deep Tissue Abscess Cavities,' with ClinicalTrials.gov identifier NCT02240498).

First in human measurements of abscess cavity optical properties and methylene blue uptake prior to photodynamic therapy by in vivo diffuse reflectance spectroscopy

Significance

Efficacious photodynamic therapy (PDT) of abscess cavities requires personalized treatment planning. This relies on knowledge of abscess wall optical properties, which we report for the first time in human subjects.

Aim

The objective was to extract optical properties and photosensitizer concentration from spatially resolved diffuse reflectance measurements of abscess cavities prior to methylene blue (MB) PDT, as part of a phase 1 clinical trial.

Approach

Diffuse reflectance spectra were collected at the abscess wall of 13 human subjects using a custom fiber-optic probe and optical spectroscopy system, before and after MB administration. A Monte Carlo lookup table was used to extract optical properties.

Results

Pre-MB abscess wall absorption coefficients at 665 nm were 0.15 ± 0.1    cm - 1 (0.03 to 0.36    cm - 1 ) and 10.74 ± 15.81    cm - 1 (0.08 to 49.3   cm - 1 ) post-MB. Reduced scattering coefficients at 665 nm were 8.45 ± 2.37    cm - 1 (4.8 to 13.2    cm - 1 ) and 5.6 ± 2.26    cm - 1 (1.6 to 9.9    cm - 1 ) for pre-MB and post-MB, respectively. Oxygen saturations were found to be 58.83 % ± 35.78 % (5.6% to 100%) pre-MB and 36.29 % ± 25.1 % (0.0001% to 76.4%) post-MB. Determined MB concentrations were 71.83 ± 108.22    μ M (0 to 311    μ M ).

Conclusions

We observed substantial inter-subject variation in both native wall optical properties and MB uptake. This underscores the importance of making these measurements for patient-specific treatment planning.

Treatment planning for photodynamic therapy of abscess cavities using patient-specific optical properties measured prior to illumination

Background

Photodynamic therapy (PDT) is an effective antimicrobial therapy that we used to treat human abscess cavities in a recently completed Phase 1 clinical trial. This trial included pre-PDT measurements of abscess optical properties, which affect the expected light dose to the abscess wall and eventual PDT response.

Purpose

The objective of this study was to simulate PDT treatment planning for the 13 subjects that received optical spectroscopy prior to clinical abscess PDT. Our goal was to determine the impact of these measured optical properties on our ability to achieve fluence rate targets in 95% of the abscess wall.

Methods

During a Phase 1 clinical trial, 13 subjects received diffuse reflectance spectroscopy prior to PDT in order to determine the optical properties of their abscess wall. Retrospective treatment plans seeking to achieve fluence rate targets in 95% of the abscess wall were evaluated for all subjects for 3 conditions: (1) at the laser power delivered clinically with assumed optical properties, (2) at the laser power delivered clinically with measured optical properties, and (3) with patient-specific treatment planning using these measured optical properties. Factors modified in treatment planning included delivered laser power and intra-cavity Intralipid (scatterer) concentration. The effects of laser fiber type were also simulated.

Results

Using a flat-cleaved laser fiber, the proportion of subjects that achieved 95% abscess wall coverage decreased significantly when incorporating measured optical properties for both the 4 mW/cm 2 (92% vs. 38%, p=0.01) and 20 mW/cm 2 (62% vs. 15%, p=0.04) fluence rate thresholds. However, when measured optical properties were incorporated into treatment planning, a fluence rate of 4 mW/cm 2 was achieved in 95% of the abscess wall for all cases. In treatment planning, the optimal Intralipid concentration across subjects was found to be 0.14 ± 0.09% and the optimal laser power varied from that delivered clinically but with no clear trend (p=0.79). The required laser power to achieve 4 mW/cm 2 in 95% of the abscess wall was significantly correlated with measured µ a at the abscess wall (ρ=0.7, p=0.008), but not abscess surface area (ρ=0.2, p=0.53). When using spherical diffuser fibers as the illumination source, the optimal intralipid concentration decreased to 0.028 ± 0.026% (p=0.0005), and the required laser power decreased also (p=0.0002), compared to flat cleaved fibers. If the intra-cavity lipid emulsion (Intralipid) was replaced with a non-scattering fluid, all subjects could achieve the 4 mW/cm 2 fluence rate threshold in 95% of the abscess wall using a spherical diffuser, while only 69% of subjects could reach the same criterion using a flat cleaved fiber.

Conclusions

The range of optical properties measured in human abscesses reduced coverage of the abscess wall at desirable fluence rates. Patient-specific treatment planning including these measured optical properties could bring the coverage back to desirable levels by altering the Intralipid concentration and delivered optical power. These results motivate a future Phase 2 clinical trial to directly compare the efficacy of patient-specific-treatment planning with fixed doses of Intralipid and light.Clinical Trial Registration: The parent clinical trial from which these data were acquired is registered on ClinicalTrials.gov as "Safety and Feasibility Study of Methylene Blue Photodynamic Therapy to Sterilize Deep Tissue Abscess Cavities," with ClinicalTrials.gov identifier NCT02240498 .

Photodynamic therapy is a safe and feasible adjunct to percutaneous drainage of deep tissue abscesses: Results of a first in humans Phase 1 clinical trial

Background

Standard of care for abscess management includes image-guided percutaneous drainage and antibiotics. However, cure rates vary between patients and there is growing concern for antibiotic-resistant bacteria. Photodynamic therapy (PDT), which utilizes light-activated dyes to generate cytotoxic reactive species, could complement the standard of care by sterilizing the abscess at time of drainage.

Purpose

The goal of this study was to perform a first in humans Phase 1 clinical study evaluating safety and feasibility of PDT with methylene blue (MB) at the time of percutaneous abscess drainage. This was accomplished through an open-label dose escalation study, with duration of light delivery escalated from 5-30 minutes.

Materials and Methods

We performed MB-PDT in 18 subjects undergoing percutaneous abscess drainage. Following standard of care drainage, 1 mg/mL MB was delivered for 10 minutes. MB was aspirated, and 1% lipid emulsion infused to homogenize light dose at the cavity wall. An optical fiber was advanced to the approximate center of the abscess for 665 nm laser illumination at 20 mW/cm 2 .

Results

MB-PDT at the time of abscess drainage was safe and feasible in all cases, with no evidence of fat embolism due to lipid emulsion or adverse reaction to MB observed. No study-related adverse or serious adverse events were encountered, and the procedure was well tolerated by all subjects. While the study was not designed or powered to determine efficacy, time to resolution of clinical symptoms was significantly decreased in subjects receiving higher fluences (p=0.028). Additionally, drainage catheter output post-procedure was decreased in subjects receiving higher fluences (ρ=-0.18), although this difference was not significant (p=0.43).

Conclusion

MB-PDT is a safe and feasible adjunct to image-guided percutaneous abscess drainage. Clinical measures indicate a dose-dependent response to PDT, motivating future Phase 2 studies evaluating the efficacy of MB-PDT in this patient population.

First in human measurements of abscess cavity optical properties and methylene blue uptake prior to photodynamic therapy by in vivo diffuse reflectance spectroscopy

Significance

Efficacious photodynamic therapy (PDT) of abscess cavities requires personalized treatment planning. This relies on knowledge of abscess wall optical properties, which we report for the first time in human subjects.

Aim

The objective was to extract optical properties and photosensitizer concentration from spatially-resolved diffuse reflectance measurements of abscess cavities prior to methylene blue (MB) PDT, as part of a Phase 1 clinical trial.

Approach

Diffuse reflectance spectra were collected at the abscess wall of 13 human subjects using a custom fiber-optic probe and optical spectroscopy system, before and after MB administration. A Monte Carlo lookup table was used to extract optical properties.

Results

Pre-MB abscess wall absorption coefficients at 665 nm were 0.15±0.1 cm -1 (0.03-0.36 cm -1 ) and 10.74±15.81 cm -1 (0.08-49.3 cm -1 ) post-MB. Reduced scattering coefficients at 665 nm were 8.45±2.37 cm -1 (4.8-13.2 cm -1 ) and 5.6±2.26 cm -1 (1.6-9.9 cm -1 ) for pre-MB and post-MB, respectively. Oxygen saturations were found to be 58.83±35.78% (5.6-100%) pre-MB and 36.29±25.1% (0.0001-76.4%) post-MB. Determined MB concentrations were 71.83±108.22 µM (0-311 µM).

Conclusions

We observed substantial inter-subject variation in both native wall optical properties and methylene blue uptake. This underscores the importance of making these measurements for patient-specific treatment planning.