MEDICAL DOSIMETRY – CONE BEAM COMPUTED TOMOGRAPHY DOSIMETRIC STUDIES
Cone-Beam Computed Tomography (CBCT) enables high-resolution volumetric scanning of the bone and soft tissue anatomy under investigation at the treatment accelerator. In this study we were able to simulate a kV imaging system, installed on a linear accelerator, used to perform CBCT scans. A good agreement achieved between the Monte Carlo (MCNPX) simulations and the experimental results was obtained. In order to assess the Entrance Surface Dose (ESD) distribution in different CBCT examinations, the location of the isocentre of the system was modified according to the chosen scanning protocol. For the Head protocol, the isocentre of the system was set at the hypophysis of the Golem voxel phantom to simulate a CBCT scan acquisition for a brain tumor location. The isodose curves obtained allowed to identify how ESD is distributed along the clinically selected field of views (FOVs), remaining high along their diameter. The FOV dimensions are greater than the clinical beam width whereby ESD values decreases rapidly outside the primary X-ray beam.
MCNPX simulation workflow: A) Validation of the CBCT imaging system; B) Implementation of the Golem voxel phantom; C) ESD assessment for the Head protocol (isocenter at hypofisis); D) Isodose curves for ESD distribution for a single axial Head CBCT scan.
- Baptista, M; Di Maria, S.; Vieira, S.; Vaz, P.; “Entrance Surface Dose distribution and organ dose assessment for Cone-Beam Computed Tomography using measurements and Monte Carlo simulations with voxel phantoms” (2017); vol.140, pp. 428-434; doi: 10.1016/j.radphyschem.2017.02.018