Feasibility of antimicrobial photodynamic therapy for treatment of breast abscesses: Retrospective Monte Carlo simulation study

Breast abscesses are a common issue that affects both breastfeeding and nonpuerperal patients. Even with image-guided drainage and antibiotics, these recur frequently due to unresolved infection. One potential adjunct treatment is photodynamic therapy (PDT), which uses photosensitive compounds to generate cytotoxic reactive oxygen species. Here, we investigate the feasibility of using antimicrobial PDT to treat breast abscesses through a retrospective Monte Carlo simulation study. This study included adult subjects that had ultrasound-guided breast abscess aspiration over a five-year period at our institution (n = 119). Pre-procedure ultrasound images were segmented and used to produce either idealized ellipsoidal volumes or extrapolated segmented volumes for simulated PDT treatment planning. We investigated the effects of abscess wall optical properties and the presence of intra-cavity scattering on our ability to achieve target fluence rates of 4 or 20 mW/cm² in 95% of the abscess wall. Without intra-cavity scattering, eligibility at the 4 mW/cm² fluence rate target ranged from 99.2%-100% for ellipsoidal volumes and 76.1%-80.7% for segmented volumes. With intra-cavity scattering added, eligibility at the 4 mW/cm² target increased significantly to 93.4%-100% for segmented volumes (p < 0.0001). However, this required significantly higher optical power (p < 0.0001). PDT therefore appears to be feasible in this patient population and merits further investigation.