Effects of Patient-specific Treatment Planning on Eligibility for Photodynamic Therapy of Deep Tissue Abscess Cavities: Retrospective Monte Carlo Simulation Study

Significance: Antimicrobial photodynamic therapy (PDT) effectively kills bacterial strains found in deep tissue abscess cavities. PDT response hinges on multiple factors, including light dose, which depends on patient optical properties.

Aim: Computed tomography images for 60 abscess drainage subjects were segmented and used for Monte Carlo (MC) simulation. We evaluated effects of optical properties and abscess morphology on PDT eligibility and generated treatment plans.

Approach: A range of abscess wall absorptions (μa  ,  wall) and intra-cavity Intralipid concentrations were simulated. At each combination, the threshold optical power and optimal Intralipid concentration were found for a fluence rate target, with subjects being eligible for PDT if the target was attainable with <2000  mW of source light. Further simulations were performed with absorption within the cavity (μa  ,  cavity).

Results: Patient-specific treatment planning substantially increased the number of subjects expected to achieve an efficacious light dose for antimicrobial PDT, especially with Intralipid modification. The threshold optical power and optimal Intralipid concentration increased with increasing μa  ,  wall (p  <  0.001). PDT eligibility improved with patient-specific treatment planning (p  <  0.0001). With μa  ,  wall  =  0.2  cm  -  1, eligibility increased from 42% to 92%. Increasing μa  ,  cavity reduced PDT eligibility (p  <  0.0001); modifying the delivered optical power had the greatest impact in this case.

Conclusions: MC-based treatment planning greatly increases eligibility for PDT of abscess cavities.