Photodynamic therapy (PDT) is based on the generation of highly reactive singlet oxygen through interactions of
photosensitizer, light and molecular oxygen. PDT has become a clinically approved, minimally invasive therapeutic
modality for a wide variety of malignant and nonmalignant diseases. The main dosimetric parameters for predicting the
PDT efficacy include the delivered light dose, the quantification and photobleaching of the administrated photosensitizer,
the tissue oxygen concentration, the amount of singlet oxygen generation and the resulting biological responses. This
review article presents the emerging optical techniques that in use or under development for monitoring dosimetric
parameters during PDT treatment. Moreover, the main challenges in developing real-time and noninvasive optical
techniques for monitoring dosimetric parameters in PDT will be described.