Biomedical Optics 6 MCQ

Photodynamic Therapy (PDT)

• PDT is a 120-minute session
• Presented by Dr. Marjaneh Hejazi
• Duration of session is 120 minutes
• Date of presentation: 12/13/2021

Learning Objectives

• Understanding the necessity of radiation dosimetry for treatment planning in biomedical applications
• Learning about laser applications
• Introduction of medical physicists in therapeutic hospital departments

Keywords

• Photodynamic therapy
• Physics
• Dosimetry

References

• Zhu, T.C., & Finlay, J.C. (2008). The role of photodynamic therapy (PDT) physics. Medical physics, 35(7Part1), 3127-3136.
• Kim, M.M., & Darafsheh, A. (2020). Light sources and dosimetry techniques for photodynamic therapy. Photochemistry and photobiology, 96(2), 280-294.
• Makropoulou, M., Kareliotis, G., Spyratou, E., Drakaki, E., Serafetinides, A.A., & Efstathopoulos, E. (2019). Non-ionizing, laser radiation in Theranostics: The need for dosimetry and the role of Medical Physics. Physica Medica, 63, 7-18.

Recommended Article

• Combination of Photodynamic Therapy with Radiotherapy for Cancer Treatment

Today's Content

• Introductory remarks on laser radiation
• Laser-tissue interactions and photobiological mechanisms
• Biomedical laser applications in phototherapy
• Current areas of basic PDT research
• PDT dosimetry
• PDT future research
• Summary

1. Introductory Remarks

• Laser discovery in 1960
• Emphasis in 21st century
• Enthusiasm in the field

2. Laser Radiation

• Definition, properties, and biomedical applications
• Lasers for cosmetic applications (wrinkle removal, hair removal)
• Different wavelengths and their applications (e.g., 1320nm, Er, CO2, KTP, Ruby, Nd:YAG, 1450nm)
• Properties of lasers and their application
• Advantages of lasers

3. Laser-Tissue Interactions and Photobiological Mechanisms

• Photochemical effects resulting from molecular photo-excitation via photon absorption
• Chemical reactions such as production of free radicals and reactive oxygen species (ROS)
• Interactions between power density and exposure time

4. Biomedical Laser Applications

• Photodynamic therapy (PDT) of tumors
• Biostimulation for wound healing (low-level laser therapy)
• Photochemical ablation and photodisruption

4. Definition of PDT

• Light-activated chemotherapy using photosensitive drug accumulation
• Causing oxidative injury to cells

4. PDT Technique

• Non-invasive technique employing three factors:
  • Photosensitizing agent (PS) for targeting malignant cells
  • Molecular oxygen (O2) producing reactive singlet oxygen
  • Non-thermal monochromatic light irradiation

4. Type II Mechanism

• Photon absorption by the sensitizer
• Energy transfer to oxygen creating reactive singlet oxygen

4. Singlet Oxygen

• An unstable form of molecular oxygen
• A key factor in PDT's mechanism of action

5. Current Areas of Basic PDT Research

• Photon use in the 600-850nm region of the electromagnetic spectrum
• Diode lasers are fixed wavelength, and a unique laser unit is required for each photosensitizer
• Clinical diode lasers provide up to 1 W/cm^2 irradiance
• Diode lasers with outputs between 415-690 nm wavelength are commonly used in PDT

5. Dosimetry

• Implicit Dosimetry: Using a metric (like photobleaching) that incorporates dose factors indirectly.
• Explicit Dosimetry: Measuring each dose parameter separately and combining them using a model.
• Direct Dosimetry: Method of directly measuring parameters in PDT

6. PDT Future Research

• Efficacy in various malignant/premalignant conditions (head/neck, lung cancer, mesothelioma, Barrett's esophagus, prostate cancer, and brain tumors)
• Targeted delivery of photosensitizers with nanotechnology
• Synthesis of high tumor uptake selectivity nanoparticles

6. PDT Future Steps

• Combining external beam radiation therapy
• Using radioluminescence of nanoparticles
• Down-converting xray radiation into visible light for adjacent photosensitizer activation

6. PDT Future (cont.)

• High energy delivered (4-5 orders higher than in radiation therapy)
• Miniaturized wireless implantable device with LEDs for local light delivery and dosimetry

Conclusion

• Need for well-trained medical physicists in both radiation and laser-matter interactions, for dosimetry, treatment planning and safety
• Bridging ionizing radiation and non-ionizing laser radiation in oncology treatment

Summary

• PDT is a light-activated chemotherapy used in treating various diseases.
• It depends on the combination of photosensitizing agent, molecular oxygen, and light irradiation.
• Safety for patients and medical personnel relies on qualified expertise.
• Ongoing research focuses on better understanding of photobiological mechanisms and optimization of clinical applications.