Patient-specific approach of CBCT imaging: custom made Monte Carlo simulations
To quantify the amount of radiation dose and determine the actual risk from X-ray exposures the effective dose has to be determined. Firstly, the absorbed dose to radiosensitive organs which quantifies the amount of energy deposited in them should be estimated. There is a number of studies in the literature focusing on the measurement of organ doses and estimation of effective doses in dental CBCT using TLDs placed in anthropomorphic phantoms. Nevertheless, patient dose and associated risks will vary between individuals, with patient size and mass as main factors.
Monte Carlo (MC) simulation using voxel-based anthropomorphic phantoms is a flexible and accurate alternative method to the direct measurement of organ and effective doses in phantoms. The radiation transport MC methods involve the use of random numbers to sample probability distributions to determine the energy, direction, position and path length of the individual particles and the physical interactions the particles undergo.
Although MC is frequently used in CBCT for radiotherapy, there is little evidence in literature on the use of MC in dental CBCT. This project builds on the work performed in the ‘Monte Carlo’ part of the OT project titled ‘Development of a cone beam CT-based surgical planning technique with standardized and accurate jaw bone quantification at a low radiation dose’ (OT/08/057) and on the dosimetric work performed in the multicenter project ‘SEDENTEXCT: Safety and Efficacy of a New and Emerging Dental X-ray Modality’, funded by the European Atomic Energy Community’s Seventh Framework programme FP7/2007-2011. The OT/08/057 project resulted in the development of an accurate, efficient and flexible simulation tool for quality assurance, system evaluation and optimization of CBCT equipment which was adopted to model the system structure and the image acquisition geometry and applied to calculate radiation doses, to assess the dose distribution and to investigate the dose influential factors. The SEDENTEXCT project focused on various factors related to the appropriate use of CBCT in dental practice. One of the key work packages within SEDENTEXCT encompassed various dosimetric tasks, including Monte Carlo simulations, anthropomorphic and geometric phantom dosimetry, and in vivo (i.e. patient’s skin) dose measurements. The aim of this project is to perform patient-specific dosimetry by accurately calculating organ doses and radiation-induced cancer risk in dental CBCT with a special focus on paediatric patients.
The overall project aim can be divided into the following sub-objectives:
Objective 1: To customize an existing Monte Carlo framework towards patient-specific applications.
Objective 2: To validate the Monte Carlo framework and the patient-specific voxel phantoms.
Objective 3: To calculate organ doses for various age groups.
Objective 4: To estimate the actual radiation induced risk from these doses using recent dose risk modeling approaches.