Photodynamic therapy of deep tissue abscess cavities: Retrospective image‐based feasibility study using Monte Carlo simulation

Abstract

Purpose: Deep tissue abscesses remain a serious cause of morbidity, mortality, and hospital stay despite development of percutaneous drainage and increasing use of perioperative antibiotics. The goal of this study was to examine the feasibility of methylene blue (MB) mediated photodynamic therapy (PDT) for treatment of infected abscesses with intracavity MB delivery, using computed tomography (CT) imaging data from a representative abscess patient population and Monte Carlo simulation of light delivery. Methods: This retrospective study included all adult subjects that received percutaneous abscess drainage between 1 January 2014 and 31 December 2014 at our institution whose abscess was confirmed by abdominal CT imaging less than 1 week preprocedure (n = 358). Of these, 40 subjects were further analyzed with Monte Carlo simulation. Abscess volumes were segmented from CT images, and imported into the Monte Carlo simulation space. Monte Carlo simulations were performed with a single fiber placement for each abscess, with the optical power at which a fluence rate of either 4 or 20 mW/cm 2 was achieved for 95% of the abscess wall recorded. Subjects for which a fluence rate of 4 mW/cm 2 was attainable in 95% of the abscess wall with a maximum input optical power of 2000 mW were considered eligible for MB-PDT. Results: 42.5% of subjects would have been eligible for MB-PDT, with 17.5% attaining the higher threshold of 20 mW/cm 2 in 95% of the abscess wall, given a 1% Intralipid concentration within the abscess cavity and the assumed abscess wall optical properties. The mean optical power necessary was 680 AE 580 mW for the 4 mW/cm 2 threshold, and 1100 AE 600 mW for the 20 mW/cm 2 threshold. Abscess surface area and threshold optical power were correlated (Spearman q = 0.73, P = 0.001), with larger abscesses requiring higher optical power. Of the subjects who were not eligible for MB-PDT, abscess volumes (150 AE 120 vs 62 AE 41 cm 3 , P = 0.0049) and surface areas (320 AE 200 vs 140 AE 70 cm 2 , P = 0.0015) tended to be larger than for those who were eligible. There were no significant differences in eligibility, optical power required, or abscess volume or surface area based on abscess location. For all eligible subjects, at the optical power necessary to achieve 4 mW/cm 2 in 95% of the abscess wall, 2.5 AE 3.7% (0%-13.2%) of the wall experienced a fluence rate greater than or equal to 400 mW/cm 2 . At the 20 mW/cm 2 threshold, 8.8 AE 11.4% (0%-31.1%) of the wall surpassed this 400 mW/cm 2 level. If subjects with greater than 5% of the wall exceeding 400 mW/cm 2 are treated as ineligible, overall eligibility becomes 32.5% for the 4 mW/cm 2 threshold and 10.0% for the 20 mW/cm 2 threshold. Conclusions: Assuming that the subjects analyzed were representative of the overall patient population, over 150 patients that received percutaneous abscess drainage during the study period would have been eligible for MB-PDT at the time of drainage, with smaller abscesses being more amenable for treatment. This technique could potent...

Effects of patient-specific treatment planning on eligibility for photodynamic therapy of deep tissue abscess cavities: retrospective Monte Carlo simulation study

“…By modifying the concentration of Intralipid within the cavity and the optical power delivered, we generate patient-specific treatment plans that aim to achieve a target fluence rate at the abscess wall while minimizing the delivered optical power. We hypothesize that this will increase eligibility for MB-PDT compared with our previous study, 17 while minimizing risk to potential subjects. Further, we investigate the effects of absorption within the cavity, corresponding to leakage of MB into the cavity following aspiration.…”

“…For the second case, we allowed absorption within the cavity to increase. In previous studies, 17 we assumed zero absorption within the abscess cavity. However, a small amount of MB could leak into the abscess, causing the absorption coefficient inside the abscess to be slightly higher than zero (0 to MB, resulting in to ).…”

“…In a previous Monte Carlo (MC) study, we estimated that of abscess patients treated at our institution would be eligible for MB-PDT. 17 However, this prior MC study assumed that the uniform dose applied in the current phase 1 trial would be prescribed to all potential subjects.…”

“… 33 Although we have previously used MC simulation to examine eligibility for MB-PDT of abscesses, this prior study did not include the effects of changing optical properties or patient-specific treatment plans. 17 …”

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

“…This algorithm will generate the coordinates for the optimal source position that will be transferred to an electromagnetic (EM) navigation system, which helps the surgeon to guide the spherical bulb diffuser to the OSL. Baran et al investigated intracavity PDT of deep‐seated drained abscesses with complex geometries . The light distribution was calculated by means of Monte Carlo (MC) simulations.…”