Monte Carlo analysis of light fluence rate distribution in pleural photodynamic therapy: a study of geometric and optical property effects on treatment delivery

J Biomed Opt. 2026 Jan;31(1):018001. doi: 10.1117/1.JBO.31.1.018001. Epub 2026 Jan 5.

ABSTRACT

SIGNIFICANCE: Pleural photodynamic therapy (PDT) faces significant dosimetry challenges due to complex light distribution patterns within the pleural cavity, where integrating sphere effects dominate light propagation. Accurate prediction of light fluence rate distributions is essential for optimizing treatment protocols and improving therapeutic outcomes in this emerging clinical application.

AIM: The aim is to quantitatively analyze light fluence rate distributions in pleural PDT using Monte Carlo (MC) simulations in various cavity geometries and tissue optical properties, providing essential data for treatment planning.

APPROACH: Graphics processing unit-accelerated MC simulations ( ${10}^8\text{photons}$ ) using MCmatlab analyzed light distribution in spherical cavities (radii 0.2 to 10 cm) and anatomically realistic lung cavity models (volume = 2 L) with point sources. Simulations include a range of tissue optical properties ( ${\mu }_a$ : 0.1 to $1.0{\mathrm{cm}}^{–1}$ ; ${\mu }_s^{‘}$ : 5 to $40{\mathrm{cm}}^{–1}$ ) for a flat-cut fiber source inside a realistic three-dimensional (3D) lung geometry, including realistic thoracotomy access openings and different fill media (air versus saline). Experimental validation is made using isotropic detectors in the same 3D-printed lung phantom with varying optical properties.

RESULTS: MC statistical uncertainties averaged 1.9% across all voxels. Spherical cavities ( $r=4\mathrm{cm}$ ) demonstrated highly uniform scattered light distribution along cavity-tissue boundaries (distribution uniformity 4.9%), whereas anatomically realistic lung phantoms showed greater heterogeneity (49.9%). Scattered light fluence rate per source power ( ${\varphi }_s/S$ ) strongly correlated with tissue optical properties, particularly scattering coefficients. Source position minimally affected scattered light patterns, though direct components remained position-dependent. Side openings reduced scatter fluence near access points, with saline-filled cavities showing slightly higher fluence rates than air-filled cavities.

CONCLUSIONS: We demonstrate that patient-specific factors including cavity geometry, tissue optical properties, and surgical access considerations significantly influence light distribution in pleural PDT. The quantitative relationships established between these parameters and fluence patterns provide essential data for developing personalized treatment planning protocols to optimize therapeutic light delivery.

PMID:41498054 | PMC:PMC12768299 | DOI:10.1117/1.JBO.31.1.018001