Correlation analysis of organ doses determined by Monte Carlo simulation with dose metrics for patients undergoing chest-abdomen-pelvis CT examinations

Evaluation of direct point dose estimation based on the distribution of the size-specific dose estimate

The aim of this study was to evaluate the point doses using a distribution of the size-specific dose estimate (SSDE) from axial CT images of in-house phantoms having diameters from 8 to 40 cm. In-house phantoms made of polyester-resin (PESR) mixed with methyl ethyl ketone peroxide (MEKP) were used. The phantoms were built with different diameter sizes of 8, 16, 24, 32, and 40 cm. The phantoms were scanned by Siemens a SOMATOM Perspective-128 slice CT scanner with constant input parameters. The point doses were interpolated from the central SSDE (SSDEc) and the peripheral SSDE (SSDEp). The SSDEc and SSDEp were calculated from the SSDE with h- and k-factors. The point doses were compared to the direct measurements using the nanoDot™ optically-stimulated luminescence dosimeter (OSLD) in dedicated holes on the phantoms. It was found that the point dose decreases as the phantom diameter increased. The doses obtained using two approaches differed by 11% on average. The highest difference was 40% and the lowest difference was < 1%. It was found that dose based on the SSDE concept tended to be higher compared to the measured dose by OSLD. Point dose estimation using the concept of SSDE distribution can be considered an alternative for accurate and simple estimation. This approach still requires improvements to increase its accuracy and its application to estimate the organ dose needs further investigation.

An inventory of patient-image based risk/dose, image quality and body habitus/size metrics for adult abdomino-pelvic CT protocol optimisation

PURPOSE

Patient-specific protocol optimisation in abdomino-pelvic Computed Tomography (CT) requires measurement of body habitus/size (BH), sensitivity-specificity (surrogates image quality (IQ) metrics) and risk (surrogates often dose quantities) (RD). This work provides an updated inventory of metrics available for each of these three categories of optimisation variables derivable directly from patient measurements or images. We consider objective IQ metrics mostly in the spatial domain (i.e., those related directly to sharpness, contrast, noise quantity/texture and perceived detectability as these are used by radiologists to assess the acceptability or otherwise of patient images in practice).

MATERIALS AND METHODS

The search engine used was PubMed with the search period being 2010-2024. The key words used were: 'comput* tomography', 'CT', 'abdom*', 'dose', 'risk', 'SSDE', 'image quality', 'water equivalent diameter', 'size', 'body composition', 'habit*', 'BMI', 'obes*', 'overweight'. Since BH is critical for patient specific optimisation, articles correlating RD vs BH, and IQ vs BH were reviewed.

RESULTS

The inventory includes 11 BH, 12 IQ and 6 RD metrics. 25 RD vs BH correlation studies and 9 IQ vs BH correlation studies were identified. 7 articles in the latter group correlated metrics from all three categories concurrently.

CONCLUSIONS

Protocol optimisation should be fine-tuned to the level of the individual patient and particular clinical query. This would require a judicious choice of metrics from each of the three categories. It is suggested that, for increased utility in clinical practice, more future optimisation studies be clinical task based and involve the three categories of metrics concurrently.

Comparison of average Water Equivalent diameter values between CTContour and vendor-specific estimates in CT dosimetry

PURPOSE

This study aimed to compare the average Water Equivalent Diameter (WED) values obtained from CTContour, an open-source program for Size-Specific Dose Estimate (SSDE) and WED calculation, and vendor-specific values provided by Philips scanners.

METHODS

A random sample of 50 adult and 50 paediatric abdomen-pelvis protocol CT images from Philips scanners were chosen at our Hospital and analysed using CTContour, and extracting average WED values from Philips from the images DICOM headers. The average WED values from the two methods were compared via Bland-Altman analysis to assess their agreement and reliability.

RESULTS

The average WED values obtained from CTContour were found to be slightly lower than those obtained from the vendor-specific calculations, with mean disagreements of -5.62% and -2.88% for the adult and paediatric datasets, respectively, with both methods providing clinically acceptable estimations of average WED. There was no statistically significant correlation between body habitus and the level of disagreement between methods.

CONCLUSIONS

This study demonstrates that CTContour can provide average WED measurements comparable to the vendor-specific calculations for SSDE and WED in CT dosimetry. Differences between programs are likely due to inherent differences in the methods employed to estimate WED automatically. Further research is warranted to validate these results for additional CT protocols beyond abdomen-pelvis studies.

Cancer risk in healthy patients who underwent chest tomography comparing three different technologies

This research aimed to estimate the risk of cancer associated with patients without previous disease undergoing chest tomography. Siemens CT scanners have 6, 64, and 128 detectors. The Biologic Effects of Ionizing Radiation Reports - BEIR VII methodology was used. The study presented a sample of 64 patients aged between 18 and 80 years, in the city of Belo Horizonte, Minas Gerais - Brazil. The IMPACT CT software and CalDose X CT Online were used to calculate the absorbed and equivalent dose from the Volumetric Computed Tomography Dose Index - CTDIvol (mGy) and Dose Length Product - DLP values provided by the equipment. CT-Expo Software was also used to estimate Specific Dose Estimates (SSDEs) values. The CTDvol results for the MG1, MG,2 and MG3 Diagnostic Centers in mGy were respectively 4.369 ± 1.352, 6.99 4 ± 1.53,3 and 9.984 ± 2.282 and the SSDE values were 3.800, 6.40,0 and 9,.500. The values for the equivalent dose, at the MG2 Diagnostic Center, by IMPACT CT, in (mSv) for the breasts, esophagus, heart, thyroid, lung and thymus were respectively 3.9, 5.7, 4.7, 1.0, 4.8 and 5.7. The CalDose Software, for the same equipment and the same organs, in mSv, estimated the values 7.4, 9.4, 11.1, 5.3, 10.8 and 11.3 for women and 7.1, 9.3, 11.0, 5.3, 10.2 and 10.9 for men. The estimated risk of cancer decreased according to the patient's age, but with a higher incidence for females. The use of each software must be carefully analyzed to avoid undue values due to the particularities of each one. The results also showed that the risk of developing cancer due to radiation decreases with patient age and is higher in females.

Relationship between Dilution Magnification of Non-Ionic Iodinated Contrast Medium and Amplification Effect of Radiation Dose

Objective

Neuroendovascular treatments are less invasive than surgical clipping. However, the number of fluoroscopy runs may be greater when a contrast medium is used than when routine angiography is performed. Several recent studies have suggested that an iodinated contrast medium causes an increase in the radiation dose. Therefore, it is clinically important to identify physical factors causing amplification of the radiation dose. The purpose of this study was to investigate how dilution of a contrast medium with water influences the amplification effect of the radiation dose using simulation analysis.

Methods

Three different types of commercially available contrast media, namely, iopamidol, iohexol, and iodixanol, were diluted 1.7-3.3 times with water and placed in the left brain parenchyma of a numerical brain phantom. Using the Monte Carlo simulation method, the phantom was exposed to X-ray beams under constant exposure conditions, and the energy absorbed in the entire region of the left brain parenchyma was estimated. At the same time, the content and volume of a contrast medium in the cerebral vessels were predicted on the basis of pharmacokinetic and fractal analyses.

Results

The increase in absorbed energy was attributed to secondary electrons emitted from the contrast medium and varied depending on its content and volume. Interestingly, the amount of energy absorbed increased with increasing dilution of the contrast medium. Furthermore, the amplification effect of the radiation dose varied according to the type of contrast medium used.

Conclusion

These results suggest that the amplification effect of the radiation dose is closely related to an increase in the cross-sectional area in which the X-rays interact with the contrast medium, which is caused by increased distribution of contrast medium in the cerebral vessels. When the contrast medium is diluted with water, its spread in the cerebral vessels plays a more important role than its content in the amplification effect of the radiation dose.

[Organ and Effective Doses Using Automation Organ Dose Estimation Software for Lung Cancer Screening Using Low-dose Computed Tomography]

PURPOSE

The purpose of this study was to evaluate the differences in the organ doses and the effective doses using three types of automated organ dose estimation software for low-dose computed tomography (CT) screening for lung cancer and to evaluate the correlations between each dose and size-specific dose estimates (SSDEs).

METHODS

Seventy-two adults who underwent low-dose CT screening for lung cancer were included, and the organ doses and the effective doses were calculated using each of automated organ dose estimation software. We evaluated differences between software for the organ doses and the effective doses and the correlations between each dose and SSDEs.

RESULTS

Differences in organ doses and effective doses were observed among the software. The organ doses showed a strong correlation (r=0.833-0.995) with SSDEs for organs within the scan range. The effective doses showed a strong correlation (r=0.830-0.970) with SSDEs, although there were significant differences among the software.

CONCLUSION

Although the organ doses and the effective doses differed between software, it may be possible to estimate them from SSDEs by using linear regression equations.

Comparison of Application Value of Different Radiation Dose Evaluation Methods in Evaluating Radiation Dose of Adult Thoracic and Abdominal CT Scan

Objective

To explore the differences among volumetric CT dose index (CTDI_vol), body-specific dose assessment (SSDE_ED) based on effective diameter (ED), and SSDE_WED based on water equivalent diameter (WED) in evaluating the radiation dose of adult thoracic and abdominal CT scanning.

Methods

From January 2021 to October 2021, enhanced chest CT scans of 100 patients and enhanced abdomen CT scans of another 100 patients were collected. According to the body mass index (BMI), they can be divided into groups A and D (BMI < 20 kg/m²), groups B and E (20 kg/m² ≤ BMI ≤ 24.9 kg/m²), and groups C and F (BMI > 24.9 kg/m²). The CTDIvol, anteroposterior diameter (AP), and the left and rght diameter (LAT) of all the patients were recorded, and the ED, water equivalent diameter (WED), the conversion factor (f _size,ED), (f _{size, WED}), SSDE_ED, and SSDE_WED were calculated. The differences were compared between the different groups.

Results

The AP, LAT, ED, and WED of groups B, E, C, and F were higher than those of groups A and D, and those of groups C and F were higher than those of groups B and E (P < 0.05). The f _size,ED and f _{size, WED} of groups B, E, C, and F are lower than those of groups A and D, and those of groups C and F are lower than those of groups B and E (P < 0.05). CTDI_vol, SSDE_ED, and SSDE_WED in groups B, E, C, and F are higher than those in groups A and D, and those in groups C and F are higher than those in groups B and E (p < 0.05). In the same group, patients with chest- and abdomen-enhanced have higher SSDE_WED and SSDE_ED than CTDI_vol, patients with chest-enhanced CT scans have higher SSDE_WED than SSDE_ED, and patients with abdomen-enhanced CT scans have higher SSDE_ED than SSDE_WED (P < 0.05).

Conclusion

CTDIvol and ED-based SSDEED underestimated the radiation dose of the subject exposed, where the patient was actually exposed to a greater dose. However, SSDE_WED based on WED considers better the difference in patient size and attenuation characteristics, and can more accurately evaluate the radiation dose received by patients of different sizes during the chest and abdomen CT scan.

PATIENT-SPECIFIC ORGAN DOSE EVALUATION BASED ON MONTE CARLO SIMULATION AND DOSE METRICS IN PAEDIATRIC CHEST-ABDOMEN-PELVIS CT EXAMINATIONS

This study aimed to determine organ doses based on Monte Carlo (MC) simulations for individual paediatric patients undergoing chest-abdomen-pelvis computed tomography (CT) examinations and to evaluate correlations of organ doses with dose metrics. MC simulations were performed by inputting detailed descriptions of a CT scanner, scanning parameters and CT images of 51 paediatric patients aged from 0 to 10 years into the simulation software. Organ doses for six radiosensitive organs were determined from dose distribution images obtained as the simulation results. The correlations of organ doses with dose metrics such as volume CT dose index, size-specific dose estimates (SSDEs), and organ-specific SSDEs were evaluated from the corresponding coefficients of determination. Organ doses for ages of 0-1 and 1-5 years were 22%-32% lower than those for ages of 5-10 years. Organ doses exhibited higher linear correlations with SSDEs and organ-specific SSDEs, and can be easily estimated using the linear regression.