Monte Carlo-based estimation of NIR-PDT efficacy with and without breast compression in early-stage breast cancer

Near-infrared photodynamic therapy (NIR-PDT) for early-stage breast cancer has attracted attention and it suggests that the depth of the tumor from the skin surface significantly affects treatment efficacy, with shallower tumors responding more effectively to therapy. Therefore, compressing the breast, as is done during mammography, may improve therapeutic outcomes by reducing tumor depth. In this study, we investigated the effectiveness of breast compression in NIR-PDT for early-stage breast cancer using Monte Carlo simulations.

We evaluated the impact of breast compression on the effectiveness of NIR-PDT for early-stage breast cancer through Monte Carlo simulations. Sixty pairs of digital breast phantoms representing uncompressed and compressed states were generated, and spherical tumors with a 7 mm diameter were embedded under appropriate conditions in 15 of these pairs. The propagation of excitation light at an intensity of 330 mW/cm², a level considered safe for skin tissue, was then analyzed. Based on the computed excitation fluence, the corresponding amount of singlet oxygen produced was estimated to assess NIR-PDT efficacy.

The simulations indicated that breast compression substantially reduced tumor depth, with an average decrease of 5 mm across the 15 pairs. Consequently, the number of irradiation sessions required for complete treatment was reduced by an average of 19. In 8 of the 15 phantoms, the number of treatment irradiation cycles was reduced to five or fewer, suggesting clinical feasibility.

These results demonstrate that applying appropriate breast compression can enhance the therapeutic performance of NIR-PDT for early-stage breast cancer.