Abstract: Methods and systems are described for implementing a photodynamic therapy. An example method may comprise determining, during photodynamic therapy and using a plurality of optical probes spatially distributed within a patient, data indicative of one or more of a photodynamic therapy dosage, a fluence rate of a photodynamic therapy treatment light, or a reactive oxygen species concentration associated with corresponding locations of the plurality of optical probes. The example method may comprise changing, based on the data, one or more treatment parameters associated with providing a photodynamic therapy.