A study of proton activation tracer for real-time dose monitoring in radiotherapy

In proton or heavy-ion therapies, in-beam dose monitoring is a desirable feature that can enhance the accuracy of delivered dosage and potentially improve the number of treatments allowed by a facility per day. While many gammas are generated from protons or heavy-ions passing through a patient´s body, only a small fraction of these gammas are useful for locating the Bragg peaks. Extracting these gammas from the background can be more challenging than expected. This study attempts to decompose the gammas from the irradiation-induced activities into different species, spatial, energy, and time domains and applies these extracted information to typical operating parameters of proton therapy machines. In order to achieve a spatial resolution better than a few millimeters in a real-time measurement, the less abundant positron emitters that have lower activation threshold energies are considered. The study reveals that ¹²N is a problematic activation product in soft tissue for in-beam dose monitor due to its high positron energy. This result eventually leads to a search of suitable proton activation tracers for dose monitoring purpose. ⁸⁹Y was identified as a potential tracer at the end of this search but further study shows that its application is currently limited by the amount of ⁸⁹Y deliverable to a tumor site.