Size-specific dose estimations for pediatric chest, abdomen/pelvis and head CT scans with the use of GATE

Introduction of a hybrid approach based on statistical shape model and Adaptive Neural Fuzzy Inference System (ANFIS) to assess dosimetry uncertainty: A Monte Carlo study

The increasing use of ionizing radiation has raised concerns about adverse and long-term health risks for individuals. Therefore, to evaluate the range of risks and protection against ionizing radiation, it is necessary to assess the dosimetry calculation uncertainty of the absorbed dose of organs and tissues in the body. On the other hand, absorbed dose calculation with low computational load plays a noted role in dosimetry studies. Considering the Monte Carlo simulation's time-consuming and high computational cost, we present a novel model-based organ dosimetry for uncertainty evaluation. We attempt to model and estimate the organ-absorbed dose for lung organ size by combining computational phantoms and ANFIS. Two input variables were used, including variations in lung size and photon energy. The results showed that the proposed hybrid approach increased the speed of evaluation of the uncertainty of dosimetry calculations. The promising results of the hybrid approach demonstrate that it can be a suitable alternative to the time-consuming conventional methods of dosimetry calculations in dosimetry calculations, which will lead to the development of a rapid and reliable tool for organ dose estimation in dosimetry applications in the future.

Assessment of tissue-air ratios in epoxy resin and PMMA phantoms for radiation dosimetry: findings from experimental measurements and Monte Carlo simulations

This study assesses radiation doses in multi-slice computed tomography (CT) using epoxy resin and PMMA phantoms, focusing on the relationship between TAR (tissue air ratio) and kilovoltage peak (kVp). The research was conducted using a Hitachi Supria 16-slice CT scanner. An epoxy resin phantom was fabricated from commercially available materials, to simulate human tissue. The phantom contained four peripheral inserts and one central insert for dose measurement, with optically stimulated luminescent dosimeters positioned at various depths (2 to 10 cm). Monte Carlo simulations were executed using the Geant4 Application for Tomographic Emission toolkit (GATE) to model photon transport, with the x-ray spectrum generated using SpekPy software. A non-linear fitting model was developed to describe the TAR-kVp relationship across different depths for epoxy resin and PMMA. Results indicated that TAR values were higher at low depths (2 cm) and decreased with increasing depth, reflecting the x-ray beam's attenuation. For instance, at 80 kVp and 2 cm depth, the experimental TAR for PMMA was 1.102 ± 0.011, closely matching the MC simulation value of 1.110 ± 0.036, resulting in a small difference of 0.7%. At a depth of 10 cm, the experimental TAR for PMMA decreased to 0.245 ± 0.006, while the MC TAR was 0.248 ± 0.016, with a relative difference of 1.2%. Similar trends were observed for epoxy resin, where the experimental TAR ranged from 1.070 ± 0.014 at 2 cm to 0.235 ± 0.009 at 10 cm, while MC simulation values ranged from 1.080 ± 0.038 to 0.238 ± 0.017. Bland-Altman analysis confirmed these results, with mean differences of 0.008 for PMMA and 0.006 for epoxy resin, indicating high agreement between the experimental and simulated TAR values. This study highlights the importance of phantom material selection in dose assessment and the implications of TAR in dose correction within the context of diagnostic radiology.

Study of attenuation characteristics for novel neonatal head phantom in diagnostic radiology using Monte Carlo simulations and experiments

This study presents the design and validation of a neonatal head phantom using innovative heterogeneous composite materials customized to replicate the x-ray attenuation properties of neonatal cranial structures. Analysis of Hounsfield Unit (HU) data from 338 neonatal head CT scans informed the design of epoxy resin-based composites with additives such as sodium bicarbonate, fumed silica, and acetone to simulate bone, brain matter, cerebrospinal fluid (CSF) and hyperdense abnormalities. The cranial bone substitute (60% epoxy resin, 40% sodium bicarbonate) achieved a density of 1.60 g cm-3, with HU values (574.67-608.04) closely matching clinical ranges. Brain matter (95% epoxy resin, 5% acetone) achieved HU values (35.27-43.61), aligning with clinical means, while the CSF-equivalent material (80% epoxy resin, 15% fumed silica, 5% acetone) matched neonatal CSF HU values (14.53-17.02). A mass substitute for hyperdense abnormalities exhibited HU values (56.16-61.07), enabling differentiation from normal brain. Validation included Monte Carlo simulations and experimental CT imaging, showing close agreement in linear attenuation coefficients, with deviations below 11% across energy levels. Mass attenuation coefficients from simulations and XCOM software were consistent, with deviations under 0.7%, confirming the materials dosimetric reliability. The phantom, with a cylindrical geometry (9 cm diameter, 10 cm length), provides accurate attenuation properties across 80-120 kVp energy levels, with deviations below 5% between experimental CT numbers and simulation data. This phantom offers a robust platform for neonatal imaging research, enabling impactful dose optimization and imaging protocol adjustment and supports improved diagnostic accuracy in pediatric imaging.

Feasibility of size-specific organ-dose estimates based on water equivalent diameter for common head CT examinations: a Monte Carlo study

Computed tomography dose index (CTDI) is an unreliable dose estimate outside of the standard CTDI phantom diameters (16 and 32 cm). Size-specific dose estimate (SSDE) for head computed tomography (CT) examination was studied in the American Association of Physicists in Medicine Report 293 to provide SSDE coefficient factors based on water equivalent diameter as size metrics. However, it is limited to one protocol and for a fully irradiated organ. This study aimed to evaluate the dependency of normalized organ dose (ND) on water equivalent diameter as a size metric in three common protocols: routine head, paranasal sinus, and temporal bone. CTDI_wmeasurements were performed for outlined protocols in the Siemens Emotion 16-slice-configuration scanner. Geant4 Application for Tomographic Emission Monte Carlo simulation platform, coupled with ten GSF patient models, was used to estimate organ doses. CT scanner system was modeled. Helical CT scans were simulated using constructor scan parameters and calculated scan lengths of each patient model. Organ doses provided by simulations were normalized to CTDI_vol. The water equivalent diameters (D_w) of patient models were obtained via relationships betweenD_wand both effective diameter for a sample of patients' data.NDs received by fully, partially, and non-directly irradiated organs were then reported as a function ofD_w. For fully irradiated organs, brain (R²> 0.92), eyes (R²> 0.88), and eye lens (R²> 0.89) correlate well withD_w. For the rest of the results, a poor correlation was observed. For partially irradiated organs, the exception was scalp (R²= 0.93) in temporal bone CT. For non-directly irradiated organs, the exception was thyroid (R²> 0.90) and lungs (R²> 0.91) in routine head CT. ND correlates well in routine head CT than other protocols. For the most part, no relationship seems to exist betweenR²and scan percentage coverage. The results have revealed additional factors that may influence the ND andD_wrelationship, which explains the need for more studies in the future to investigate the effect of scan conditions and organ anatomy variation.

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

BACKGROUND

Computed tomography (CT) is currently known as a versatile imaging tool in the clinic used for almost all types of cancers. The major issue of CT is the health risk, belonging to X-ray radiation exposure. Concerning this, Monte Carlo (MC) simulation is recognized as a key computational technique for estimating and optimizing radiation dose. CT simulation with MCNP/MCNPX MC code has an inherent problem due to the lack of a fan-beam shaped source model. This limitation increases the run time and highly decreases the number of photons passing the body or phantom. Recently, a beta version of MCNP code called MCNP-FBSM (Fan-Beam Source Model) has been developed to pave the simulation way of CT imaging procedure, removing the need of the collimator. This is a new code, which needs to be validated in all aspects.

OBJECTIVE

In this work, we aimed to develop and validate an efficient computational platform based on modified MCNP-FBSM for CT dosimetry purposes.

MATERIAL AND METHODS

In this experimental study, a setup is carried out to measure CTDI100 in air and standard dosimetry phantoms. The accuracy of the developed MC CT simulator results has been widely benchmarked through comparison with our measured data, UK's National Health Service's reports (known as ImPACT), manufacturer's data, and other published results.

RESULTS

The minimum and maximum observed mean differences of our simulation results and other above-mentioned data were the 1.5%, and 9.79%, respectively.

CONCLUSION

The developed FBSM MC computational platform is a beneficial tool for CT dosimetry.

Optimization of paranasal sinus CT procedure: Ultra-low dose CT as a roadmap for pre-functional endoscopic sinus surgery

OBJECTIVE

To assess image quality and radiation dose associated with ultra-low dose CT protocol for patients with benign paranasal sinus diseases undergoing functional endoscopic surgery (FESS).

METHODS

We scanned the head portion of Alderson RANDO phantom on a second generation, dual-source, multidetector-row CT scanner (Siemens Definition Flash) using standard-dose and five low-dose protocols. Two radiologists assessed the image quality for each protocol to determine best ultra-low-dose protocols for imaging patients with benign paranasal sinus diseases undergoing FESS. The ultra-low-dose CT protocols were then used for scanning. Thereafter, 40 adult patients (age range 18-54 years, M:F 23:17) were scanned with the four low dose scanning protocols (10 patients per protocol). On both transverse and coronal reformatted CT images, two radiologists assessed visibility of key anatomic landmarks for FESS on a 2-point scale (1 = clear and complete visualization; 2 = suboptimal visualization). Data were analyzed with descriptive statistics and Cohen's kappa coefficient for interobserver agreement.

RESULTS

In phantom study, the lowest dose scan protocol (CTDI_vol 2.1 mGy, 70 kV, 75 mAs) was unacceptable due to poor image quality. For patient studies, both radiologists gave acceptable image quality scores for ultra-low-dose scan protocol with axial scan mode, automatic tube potential selection and tube current modulation (CTDI_vol 2.2 mGy; DLP 22.9 mGy.cm) with up to 60% lower dose compared to prior standard-dose CT (CTDI_vol 5.3 mGy; DLP 73.5 mGy.cm).

CONCLUSIONS

Ultra-low-dose CT protocol provides sufficient image quality for scanning patients undergoing functional endoscopic surgery for benign paranasal sinus diseases.