Towards a new high-contrast modality of radiotherapy: resonant combination radiotherapy.

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Recent results using synchrotron radiation show that irradiation of a heavy-atom doped tumour just above the heavy-atom?s K-edge (the energy required to liberate its innermost electron from the heavy atom) gives an energy-specific increase in photoelectric effect and toxicity. Based on this finding, a new modality of radiotherapy, ?resonant combination radiotherapy?, is proposed whereby chemical, spatial and energetic specificity are used in combination to deliver high doses to tumours with high contrast (about 10:1) compared to the dose received by surrounding tissue. In this scheme, specific heavy atoms will be delivered preferentially to a tumour using a chemical ?vector?. Multiple radiation fields will then be applied to the tumour in a fashion similar to the gamma-knife technique. However the energy of the radiation will also be carefully chosen so as to give the maximum dose enhancement to the tumour through quantum-mechanical processes believed to explain the recent results obtained using synchrotron radiation. Hence the gamma-knife will have both energetic and spatial specificity, coupled to the chemical specificity of the vector preferentially delivering heavy atoms to the tumour.

Modelling of the various radiobiological processes suggests the contrast ratio might be about 10:1 although there is some uncertainty in the data used in this model. A low-cost versatile apparatus, including a radiation source, will be constructed to remove this uncertainty through measurement of the required radiobiological data. A series of exemplar measurements will be made using Barium as a dopant. These results will then be used to further model resonant combination therapy.

Outside of the scope of this proposal, but enabled by it and as a direct follow up, the radiation source will be upgraded. It will then be used to make measurements on other heavy atoms such as gold and platinum so a wide range of vectors can be evaluated from a radiobiological standpoint for their suitability for resonant combination radiotherapy. In a separate parallel stream, again enabled by this proposal, a multiple point-source array radiation source will be developed to generate many radiation fields simultaneously giving the required dose levels for studies on phantoms and eventually for phase 1 clinical trials.