Abstract
The INTRABEAM system is a device that uses low kV X-ray radiation in the treatment of cancers. During Kypho-IORT the INTRABEAM delivers a single high dose of radiation to a metastasis in a spinal vertebra, sterilising the metastasis, before the vertebra is stabilised with PMMA. However, much remains uncertain about the dose distribution of low kV X-ray radiation in heterogeneous tissue, such as bone. Current generation planning CTs do not have sufficient resolution to resolve the trabecular architecture. Voxel averaging therefore affects the calculation of bone density values which are typically underestimated. This subsequently affects dose calculations. In this study the GEometry ANd Tracking 4 (GEANT4) code was used to develop a generic model of a spinal vertebra that includes trabecular architecture. The dose distribution of low kV X-ray radiation within this architecture was modelled using a Virtual Source Model (VSM) of the INTRABEAM and compared to the dose distribution of the same radiation in simulated CT scanned bone. The results show that the dose distribution of low kV X-ray radiation in trabecular bone is more complex than previously suggested. A spherical dose distribution is modulated by the trabecular architecture such that the energy deposition in the trabecular walls can reach five times higher than expected, while the energy deposition in the trabecular openings is reduced by upwards of 50%. With further development, this code may be incorporated into future treatment planning software resulting in improvements in the dose distribution calculations for low kV treatments such as Kypho-IORT.
Published Version
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