ABSTRACT
Reduction of margins and reliable application of doses tightly sculpted to the tumor target is a major goal of modern radiotherapy to avoid excess toxicity and promote dose escalation for increased tumor control. Conventional and novel methods of image-guided radiotherapy (IGRT) are thus increasingly well established in photon therapy for evaluation of patient geometry and tumor position directly at the treatment site. The physical properties of penetrating megavoltage photon beams enable detection of the radiation traversing the patient simultaneously to therapeutic treatment. The former physical emissions can be produced as a result of nuclear fragmentation reactions between the incoming protons and the target nuclei of the penetrated tissue, or of thermoacoustic effects induced by the energy deposition process, naturally enhanced at the Bragg peak. The detected coincidences can be attributed to radiation, either emerging from a single annihilation event or belonging to independent emissions accidentally occurring close in time.
