Photodynamic Therapy Dosimetry and Optical Properties

Photodynamic therapy (PDT) relies on the interplay of three core elements—photosensitiser, light and oxygen—to generate cytotoxic species that selectively destroy diseased tissue. Dosimetry in PDT encompasses the measurement and calculation of light dose delivery, photosensitiser uptake and reactive oxygen species production, all of which are modulated by tissue optical properties such as absorption and scattering. Understanding these interactions enables precise tailoring of treatment parameters—fluence, irradiance and photosensitiser concentration—to achieve optimal therapeutic effect while minimising damage to surrounding healthy tissue. Advances in optical imaging and sensing have improved real-time monitoring of singlet oxygen luminescence and photosensitiser photobleaching, offering surrogates for direct dosimetric assessment. Moreover, computational models of light transport and pharmacokinetic analyses of oxygen dynamics are informing adaptive protocols that account for patient-specific heterogeneity in tissue optics and physiology. Together, these developments are establishing a framework for personalised PDT dosimetry, with global implications for the treatment of cancer and other conditions in both high-resource and low-resource settings.

Research from Nature Portfolio

Recent studies have utilised accelerated proton excitation of photosensitisers to expand the concept of photodynamic therapy beyond traditional optical activation, demonstrating fluorescence and singlet oxygen generation that correlate with proton energy deposition and offering new avenues for dosimetric quantification. Advances in portable, battery-powered LED systems combined with smartphone-based fluorescence detection have been shown to deliver clinically relevant light doses and monitor photosensitiser accumulation in three-dimensional tumour models, highlighting strategies for dosimetry in low-resource settings. In vivo imaging using radiolabelled hypoxia tracers and pharmacokinetic modelling has provided detailed temporal mapping of tumour oxygenation during treatment, linking optical dosimetry with physiological responses and informing adaptive therapy protocols.

Photodynamic Therapy Dosimetry and Optical Properties publication trend

The graph below shows the total number of articles in photodynamic therapy dosimetry and optical properties across all publications each year (not limited to Nature Index journals).

Technical terms

Dosimetry: The measurement and calculation of the light dose, photosensitiser concentration and cytotoxic species generation during photodynamic therapy.

Fluence: The cumulative light energy delivered per unit area to the target tissue, typically expressed in joules per square centimetre (J/cm²).

Irradiance: The rate of light energy delivery per unit area, measured in milliwatts per square centimetre (mW/cm²).

Photosensitiser: A molecule that, upon activation by specific wavelengths of light, transfers energy to molecular oxygen to generate cytotoxic species.

Singlet oxygen: An excited form of oxygen generated by photosensitisers that causes oxidative damage to cellular structures.

Photobleaching: The light-induced irreversible loss of photosensitiser fluorescence, used as a surrogate indicator of cumulative reactive oxygen species production.

Optical properties: Intrinsic characteristics of tissue, including absorption and scattering coefficients, which determine light propagation and penetration depth.

References

1. Revisiting photodynamic therapy dosimetry: reductionist & surrogate approaches to facilitate clinical success. Physics in Medicine and Biology (2016).
2. Proton-dynamic therapy following photosensitiser activation by accelerated protons demonstrated through fluorescence and singlet oxygen production. Nature Communications (2019).
3. Low-cost photodynamic therapy devices for global health settings: Characterization of battery-powered LED performance and smartphone imaging in 3D tumor models. Scientific Reports (2015).
4. Monitoring Tumor Hypoxia Using 18F-FMISO PET and Pharmacokinetics Modeling after Photodynamic Therapy. Scientific Reports (2016).
5. Fractionated Photofrin-Mediated Photodynamic Therapy Significantly Improves Long-Term Survival. Cancers (2023).
6. High Sensitivity Singlet Oxygen Luminescence Sensor Using Computational Spectroscopy and Solid-State Detector. Diagnostics (2023).