Photodynamic therapy (PDT) is a modern minimally invasive treatment technique that has demonstrated efficiency for a wide range of clinical applications. PDT is based on the cytotoxic effect of singlet oxygen produced in biotissue as a result of irradiation with light of a specific spectral range of a photosensitizer (PS) delivered to the target area prior to the procedure.^1,2 Being highly reactive with a short radius of action, the produced singlet oxygen causes damage in cells contacting with PS, thus providing a local impact with minimal effects on the surrounding normal tissue. Currently, PDT is actively employed for antitumor treatment^3,4 and is being involved into anti-inflammatory treatment due to antimicrobial action, including cases of microbes resistant to traditional drug treatment.⁵ PDT also demonstrates positive aesthetic effects, such as skin rejuvenation, that have been well documented in a number of clinical trials.⁶ Both anti-inflammatory treatment and aesthetic medicine applications typically employ low-dose PDT regimes⁷ with total light doses not exceeding $150{\mathrm{J}/\mathrm{cm}}^2$.

The Journal of Biomedical Optics (JBO) publishes peer-reviewed papers on the use of novel optical systems and techniques for improved health care and biomedical research.

Biodegradable and low-toxic silicon nanoparticles (SiNPs) have potential in different biomedical applications. Previous experimental studies revealed the efficiency of some types of SiNPs in tumor hyperthermia. To analyse the feasibility of employing SiNPs produced by the laser ablation of silicon nanowire arrays in water and ethanol as agents for laser tumor hyperthermia, we numerically simulated effects of heating a millimeter-size nodal basal-cell carcinoma with embedded nanoparticles by continuous-wave laser radiation at 633 nm. Based on scanning electron microscopy data for the synthesized SiNPs size distributions, we used Mie theory to calculate their optical properties and carried out Monte Carlo simulations of light absorption inside the tumor, with and without the embedded nanoparticles, followed by an evaluation of local temperature increase based on the bioheat transfer equation. Given the same mass concentration, SiNPs obtained by the laser ablation of silicon nanowires in ethanol (eSiNPs) are characterized by smaller absorption and scattering coefficients compared to those synthesized in water (wSiNPs). In contrast, wSiNPs embedded in the tumor provide a lower overall temperature increase than eSiNPs due to the effect of shielding the laser irradiation by the highly absorbing wSiNPs-containing region at the top of the tumor. Effective tumor hyperthermia (temperature increase above 42 °C) can be performed with eSiNPs at nanoparticle mass concentrations of 3 mg/mL and higher, provided that the neighboring healthy tissues remain underheated at the applied irradiation power. The use of a laser beam with the diameter fitting the size of the tumor allows to obtain a higher temperature contrast between the tumor and surrounding normal tissues compared to the case when the beam diameter exceeds the tumor size at the comparable power.

Photodynamic therapy (PDT) is an effective technique for cancer treatment based on photoactivation of photosensitizer accumulated in pathological tissues resulting in singlet oxygen production. Employment of red (660 nm) or blue (405 nm) light differing in typical penetration depth within the tissue for PDT performance provides wide opportunities for improving PDT protocols. Oxygenation dynamics in the treated area can be monitored using diffuse optical spectroscopy (DOS) which allows evaluating tumor response to treatment. In this study, we report on monitoring oxygenation dynamics in experimental tumors after PDT treatment with chlorin-based photosensitizers using red or blue light. The untreated and red light PDT groups demonstrate a gradual decrease in tumor oxygen saturation during the 7-day observation period, however, the reason is different: in the untreated group, the effect is explained by the excessive tumor growth, while in the PDT group, the effect is caused by the blood flow arrest preventing delivery of oxygenated blood to the tumor. The blue light PDT procedure, on the contrary, demonstrates the preservation of the blood oxygen saturation in the tumor during the entire observation period due to superficial action of the blue-light PDT and weaker tumor growth inhibition. Irradiation-only regimes show a primarily insignificant decrease in tumor oxygen saturation owing to partial inhibition of tumor growth. The DOS observations are interpreted based on histology analysis.

The aim of the study was to assess the capabilities of combined application of dual-wavelength fluorescence visualization and contactless skin thermometry during photodynamic therapy monitoring (PDT) of basal cell cancer. Materials and Methods. The study was performed at the University Clinic of Privolzhsky Research Medical University (Nizhny Novgorod). Nine clinically, dermatoscopically, and histologically verified foci of basal cell skin cancer were exposed to PDT sessions (wavelength of 662 nm, light dose density of 150 J/cm(2)) with systemic application of chlorin-based photosensitizer Fotoditazin. A semiconductor laser system Latus-T (Russia) was employed for irradiation. Dual-wavelength fluorescence visualization and contactless thermometry with an IR pyrometer were used to monitor the PDT sessions. Results. The PDT sessions of nine foci of basal cell cancer were carried out under the control of fluorescence imaging and contactless thermometry. Photosensitizer photobleaching in all foci amounted to 40% signifying a percent of photosensitizer involved in the photodynamic reaction. It has been shown that the combined employment of dual-wavelength fluorescence monitoring and contactless thermometry during the PDT of basal cell skin cancer allows oncologists to control simultaneously the degree of photosensitizer photobleaching and the depth of the photodynamic effect in tissues, the extent of involving the mechanisms associated with hyperthermia as well as the correctness of the procedure conducting. In the course of 9-month dynamic follow-up after the treatment, no clinical and dermatoscopic signs of recurrence were found. Conclusion. A bimodal control of PDT enables the assessment of the correctness and efficacy of the procedure performance. The contactless control of tissue heating allows ensuring the temperature mode for hyperthermia realization, while the fluorescence monitoring makes it possible to evaluate the accumulation of the photosensitizer in the tumor and the depth of the PDT action as well as to predict the procedure efficacy based on the photobleaching data. The complementary use of these techniques allows the adjustment of the mode directly in the course of the PDT procedure. The acquisition of the sufficient statistical data on the combined monitoring will result in the development of a novel PDT protocol.