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The potential application of silver and positron emission tomography for in vivo dosimetry during radiotherapy

The possible use of silver as a material for in vivo dosimetry in radiotherapy was investigated. The investigation was carried out using a positron emission tomography (PET) scanner, two clinical accelerators and a phantom with silver implants. The phantom was irradiated several times to doses between 6 and 45 Gy. The resulting activity of positron-emitting isotopes produced in the silver by photonuclear processes was measured. It was found that the two therapeutic beams with energies of 15 MV and 18 MV would produce approximately 8344 and 7013 atoms of the radioactive isotope 106Ag per Gy of absorbed dose per gram of silver. This demonstrates that it is possible to derive absorbed doses from the radioactivity induced in silver by radiation when measured with the PET scanner. Even though the physical basis for this method is found to be sound, its application, for instance to perform quality assurance of stereotactic radiotherapy, needs further study.