TABLE 3.
Comparison of advantages and limitations of photodynamic therapy (PDT) and radiotherapy (RT) as currently practiced.
| Advantages | Limitations | |||
|---|---|---|---|---|
| PDT | RT | PDT | RT | |
| Physical | Dual-selectivity (PS + light) | Deep tissue penetration | Limited light penetration | Normal tissue dose from beam entry/exit |
| Intratumoral light delivery | Homogeneous radiation attenuation in soft tissues | High optical heterogeneity | Primarily single mechanism effect (DNA damage) | |
| Endoscopic and intraoperative delivery | High technical and dosimetric precision | Complex dosimetry and photobleaching | Radiation safety, logistics | |
| Biological | Rapid cell-kill and tumor response | Differential sensitivity of tumors (death) versus normal tissues (repair) | Heterogeneity of drug pharmacokinetics and localization Energy inefficient—high input energies typically used. Requires optimal photosensitizer-light time interval | Intrinsic and treatment-induced radio-resistance |
| Multiple cytotoxic pathways and tumor targets | Energy efficient: DNA damage amplifies biological effect | Mixed immune effects of immune-priming and immune-dampening | ||
| Oxygen-independent photosensitizers available | Well defined (stochastic) dose and effect relationships | Reduced efficacy in hypoxic tumors | ||
| Minimal treatment-induced resistance | Extensively modeled biological response | Risk of radiation-induced malignancy | ||
| Potent Immune upregulation | ||||
| Clinical | Minimal systemic or regional toxicity | All tumor sites accessible using same technological platform | Implementation requires various interventional clinical specialists | Cumulative dose limiting normal tissue damage restricts repeated treatment |
| Repeatable—no “lifetime” maximum dose | Few patient or disease-related contraindications | Deep-seated and large tumors challenging | Acute and long-term toxicities | |
| Works in radioresistant tumors and in post-RT/chemotherapy/surgery recurrence | Proven curative and palliative applications | Skin photosensitivity with some PSs | Large and costly infrastructure | |
| Relatively low cost: point-of care delivery | Predictable side-effects by tissue type and dose delivered | Difficult to standardize treatment delivery due to light and PS inhomogeneities in tumor | Multi-fraction treatment can be logistically challenging for patients and introduce inter-fraction setup variability | |
| Normal tissue structure and nerve sparing | ||||