Assessment of uncertainties associated with Monte Carlo-based personalized dosimetry in clinical CT examinations

Abstract

The clinical value of x-ray computed tomography (CT) has skyrocketed in the last decade while at the same time being the main source of medical exposure to the population. Concerns regarding the potential health hazards associated with the use of ionizing radiation were raised and an appropriate estimation of absorbed dose to patients is highly desired. In this work, we aim to validate our developed Monte Carlo CT simulator using in-phantom dose measurements and further assess the impact of personalized scan-related parameters on dosimetric calculations. We developed a Monte Carlo-based CT simulator for personalized organ level dose calculations, in which the CT source model, patient-specific computational model and personalized scanning protocol were integrated. The CT simulator was benchmarked using an ionization chamber and standard CT Dose Index phantom while the dosimetry methodology was validated through experimental measurements using thermoluminescent dosimeters (TLDs) embedded within an anthropomorphic phantom. Patient-specific scan protocols extracted from CT raw data and DICOM image metadata, respectively, were fed as input into the CT simulator to calculate individualized dose profiles. Thereby, the dosimetric uncertainties associated with using different protocol-related parameters were investigated. The absolute absorbed dose difference between measurements and simulations using the ionization chamber was less than 3%. In the case of the anthropomorphic phantom, the absolute absorbed dose difference between simulations and TLD measurements ranged from −8.3% to 22%, with a mean absolute difference of 14% while the uncertainties of protocol-related input parameters introduced an extra absolute error of 15% to the simulated results compared with TLD measurements. The developed methodology can be employed for accurate estimation of organ level dose from clinical CT examinations. The validated methodology can be further developed to produce an accurate MC simulation model with a reduced computational burden.

Validation of a deterministic linear Boltzmann transport equation solver for rapid CT dose computation using physical dose measurements in pediatric phantoms

“…All four validation cases were using a CAP protocol. Akhavanallaf et al 31 . helically scanned an adult male phantom at 100 kV with TCM.…”

A Monte Carlo Platform for Characterization of X-Ray Radiation Dose in CT Imaging

“…None of these codes are optimized enough because of the lacking an optimized fan-beam CT source model [ 13 ]. This strongly decreases the efficiency of MC programs and the number of tracking photons [ 12 , 13 ]. To solve these problems, a new MC code called “MCNP-FBSM” has been proposed for the calculation of imaging parameters [ 13 ].…”

“…Somasundaram et al [ 11 ] developed an open-source MC CT dosimetry model using Fluka code. Akhavanallaf et al [ 12 ] developed an MCNP-based MC CT simulator for assessing in-phantom CT dose uncertainties. The primary step in the MC modeling of such scanners is the X-ray source simulation, where all of these codes are not optimized enough due to the lack of an optimized CT source model, removing the needs of the collimator for shaping beam into fan geometry [ 13 ].…”

“…The primary step in the MC modeling of such scanners is the X-ray source simulation, where all of these codes are not optimized enough due to the lack of an optimized CT source model, removing the needs of the collimator for shaping beam into fan geometry [ 13 ]. This problem has fatally affected the execution time of MC simulation, accuracy and precision of outcomes [ 12 , 13 ]. X-ray photons come from a bimodal focal spot profile [ 14 ] on the anode area, and then their directions are trimmed into fan geometry by lead leaves of the collimator.…”

Comparison of organ and effective dose estimations from different Monte Carlo simulation‐based software methods in infant CT and comparison with direct phantom measurements

“…In particular, LiF:Mg,Cu,P (TLD‐100H) are known to possess a superior energy and tissue equivalence compared to other thermoluminescent materials 10 . Several studies have used TLD‐100H chips to perform CT organ dosimetry within adult and pediatric anthropomorphic phantoms 11–14 . Existing computational methods for organ dose estimations are predominantly based on Monte Carlo radiation transport simulations.…”