Photodynamic therapy devices, systems and methods

A photodynamic therapy system comprising:

• an implantable illumination device comprising a light source configured to emit light having a spectrum which overlaps with an absorption peak of an absorption target and a receiver antenna coupled to the light source and configured to extract power from a radiofrequency power signal incident on the implantable illumination device;
• and
• a transmitter comprising an antenna, a powering module configured to generate a drive signal which causes the antenna to generate the radiofrequency power signal, a dosimetry module coupled to the antenna and configured to measure a power, at the antenna, of a third harmonic of the radiofrequency power signal backscattered from the implantable illumination device, and a controller configured to determine, based on the power, at the antenna, of the third harmonic of the radiofrequency power signal backscattered from the implantable illumination device, an indication of the power extracted by the implantable illumination device from the radiofrequency power signal incident on the implantable illumination device, determine a light dose emitted by the light source based on the indication of the power extracted by the implantable illumination device, and control the drive signal to control a power of the radiofrequency power signal and thereby control the light dose.