1. OPTICAL MONITORING OF PHOTOSENSITIZER DIFFUSION INTO TISSUE
Alexander V. Khilov1, Mikhail Yu. Kirillin1, Daria A. Loginova1, Alina E. Meller1,2 and Ilya V. Turchin1
1Institute of Applied Physics of Russian Academy of Science, Nizhny Novgorod, Russia
2 Nizhny Novgorod State Medical Academy, Nizhny Novgorod, Russia
International Symposium
“Saratov Fall Meeting”
26 ― 29 September 2017
Saratov, Russia

2. Basic PDT principles
Therapeutic agents + fluorescent markers for diagnostics = Theranostics
Jonathan P. Celli, et al, Chem. Rev. 2010, 110
Photodynamic therapy (PDT) is a modern photochemistry-based approach to the treatment of different pathologies, including cancer. The PDT uses light radiation of a specific wavelength and PS. Light radiation imparts cytotoxicity and photochemical reactions inducing singlet oxygen release followed by necrosis and apoptosis of cancer cells.

3. PDT benefits Low pain level Good cosmetic results
Wide range of permitted PS and light doses
Possibility of multiple procedure repetitions
Possibility to combine with other treatments
For correct choice of PDT regime it is necessary to know the distribution of PS within the treated tissue

4. Chlorine series photosensitizers
Benefits:
Fast delivery to tumor (~ 2h)
Fast biodegradation (~ 24h)
High quantum yield of singlet oxygen
Two absorption peaks
Two-wavelength probing can provide additional information!

5. Fluorescence imaging device
LED nm nm
CCD camera optical filter
Home-made setup for PDT monitoring “Fluovizor” *
LED excitation
405 nm
660 nm
μa, mm-1 (rat brain)
2.2
0.5
μs, mm-1 (rat brain)
4.5
3.5
The difference in optical properties ** of tissue and PS provides the information about the depth
* M. Kleshnin et al, Laser Phys. Lett., 12(11), 2015.
** J. Swartling et al, App. Optics, 44 (10), 2005.

6. Fluorescence model with diffusion approximation of RTE
μa(λ)+μpsa(λ), μs(λ)
Tumor R d *
For medium radius R >> d
lim 𝑑→∞ 𝑆 𝑒𝑚 =𝑐𝑜𝑛𝑠𝑡
(due to limited light penetration)
* S. Jacques, J. Biomed. Opt., 15(5), 2010.

7. Fluorescence model with Monte-Carlo simulations
μa(λ)+μpsa(λ), μs(λ)
Tumor R
μa(λ), μs(λ)
Tissue d
μa(λ)+μpsa(λ), μs(λ) R
μa(λ), μs(λ) d

8. Effect of tumor invasion depth on fluorescence signals ratio
Monte-Carlo simulations vs diffusion approximation
Diffusion approximation for different PS concentrations

9. Phantoms for model experiment
Absorption and scattering spectra
Phantom + PS
Phantom
2% Agar
PS emission
PS excitation

10. Results of model experiment
Fluorescence for nm
Fluorescence for nm
Signal ratio

11. Preliminary in vivo results
Experiment on volunteer’s hand
Revixan (in gel) as PS
Application to skin surface
30 min two-wavelength monitoring
Changes in signals ratio
Constant PS amount instead of concentration PS
Time after application

12. Preliminary in vivo results via OCT
Experiment on volunteer’s hand
Revixan (in gel) as PS
Application to skin surface
OCT monitoring
Changes in A-scans and OCT images
Control
40 s
50 s
15 min
Raw images
𝑵= 𝒊,𝒋 𝑺 𝒊,𝒋 𝒄𝒐𝒏𝒕𝒓 − 𝑺 𝒊,𝒋 𝟐
A-scans
Difference in OCT images and first control image
Control 2 s
Control 45 s
Application 40 s
Application 50 s
Application 15 min
Decrease in OCT signal and increase in N reflects PS penetration into tissue

13. Conclusion Acknowledgement
Analytical model for fluorescence from tumor tissue was presented
Monte-Carlo simulations verified analytical results
Two-wavelength probing can provide information about tumor invasion depth and PS concentration
The method can be employed to differentiate for tumor invasion depths up to 2 mm (threshold dependent on optical properties of tissue)
Preliminary in vivo results show that ratio of signals changes with PS penetration into tissue and can be used to estimate penetration depth
Changes in OCT images reflect Ps penetration into tissue
Acknowledgement
The study was supported by the Russian Science Foundation (project # )

14. Thank you for your attention!