INTRODUCTION|Simulation software has aided the estimation of organ dose from computed tomography (CT) examinations. The aim of this study was to use the CT-Expo (SASCRAD, Fritz-Reuter-Weg, Buchholz, ...Germany) software to determine volume CT dose index (CTDIvol), dose length product (DLP), organ dose and effective dose.¤METHODS|A total of 171 patient data were retrieved from a Toshiba Aquillion 16-slice CT scanner (Toshiba Corp., Tokyo, Japan) representing CT unit A and a Philips Brilliance 16-slice CT scanner (Koninklijke Philips N.V., Amsterdam, Netherlands) representing CT unit B and a CT-Expo spreadsheet was used to estimate the dose delivered.¤RESULTS|Head CT scans were the most frequently seen (64%) at the 2 facilities studied. The CT parameters of peak kilovoltage (kVp) and pitch between the 2 units were statistically different (p<0.05). There was no significant difference in CTDIvol between CT unit A and B (p=0.199). A comparison of CTDIvol and DLP of CT units A and B with other studies revealed no statistically significant difference (p<0.05). The mean effective dose (E) for the abdomen was greater compared with other studies, but without a statistically significant difference (p<0.05). Furthermore, no significant difference in organ dose was seen between CT units A and B (p=0.677). A comparison of organ dose with other studies indicated no relevant difference (p<0.05). ¤DISCUSSION AND CONCLUSION|The CT-Expo software showed good results with the imPACT software (ImPACT scanner evaluation group, London, UK). CT unit A had greater differences in CTDIvol and DLP compared with unit B. This difference could be associated with the significant difference seen in the kVp and pitch of both scanners.¤
Background
Size-specific dose estimate is gaining increased acceptance as the preferred index of CT dose in children. However it was developed based on non-clinical data.
Objective
To compare the ...accuracy of size-specific dose estimate (SSDE) based on geometric and body weight measures in pediatric chest and abdomen CT scans, versus the more accurate
SSDE
¯
(mean SSDE based on water-equivalent diameter).
Materials and methods
We retrospectively identified 50 consecutive children (age <18 years) who underwent chest CT examination and 50 children who underwent abdomen CT. We measured anteroposterior diameter (D
AP
) and lateral diameter (D
LAT
) at the central slice (of scan length) of each patient and calculated D
AP+LAT
(anteroposterior diameter plus lateral diameter) and D
ED
(effective diameter) for each patient. We calculated the following in each child: (1) SSDEs based on D
AP
, D
LAT
, D
AP+LAT
, D
ED
, and body weight, and (2) SSDE based on software calculation of mean water-equivalent diameter (
SSDE
¯
adopted standard within our study). We used intraclass correlation coefficient (ICC) and Bland–Altman analysis to compare agreement between the SSDEs and
SSDE
¯
.
Results
Gender and age distribution were similar between chest and abdomen CT groups; mean body weight was 37 kg for both groups, with ranges of 6–130 kg (chest) and 8–107 kg (abdomen). SSDEs had very strong agreement (ICC>0.9) with
SSDE
¯
. SSDEs based on D
LAT
had 95% limits of agreement of up to 43% with
SSDE
¯
. SSDEs based on other parameters (body weight, D
AP
, D
AP+LAT
, D
ED
) had 95% limits of agreement of up to 25%.
Conclusion
Differences between SSDEs calculated using various indications of patient size (geometric indices and patient weight) and the more accurate
SSDE
¯
calculated using proprietary software were generally small, with the possible exception for lateral diameter, and provide acceptable dose estimates for body CT in children.
In this study, we proposed and evaluated the validity of an optimized size-specific dose estimate, a widely used index of radiation dose in X-ray computed tomography (CT) examinations. Based on ...miscentering correction of scout images, we determined the appropriate conversion factors (CF) by using a phantom. Scans were conducted using a multi-detector CT system (Aquilion ONE, Canon Medical Systems). Four cylindrical phantoms were taken in the anteroposterior (AP) and axial directions to determine the relationship between pixel value and water-equivalent length (
L
w
). In the AP scout image, the pixel values at the selected slice positions were converted to
L
w
to calculate the water-equivalent diameter (
D
w
). The CF was derived from
D
w
and CF values before and after miscentering correction was calculated. Finally, the CF values were compared to those calculated from the axial image using the conventional methodology of the American Association of Physicists in Medicine. Before miscentering correction, the maximum difference between the CF values of the axial and scout images was 7.26%. However, after miscentering correction, the maximum difference was 1.34%. Validation using a whole-body phantom generally revealed low maximum differences between the CF from the axial image and the values from the miscentering-corrected scout images. These were 2.41% in the chest, 6.30% in the upper abdomen, 1.43% in the abdomen, and 2.45% in the pelvic region. Consequently, we concluded that our miscentering correction method for deriving the appropriate CF values based on scout images is advantageous.
Purpose of Study: The purpose of the study was to evaluate the effect of patient characteristics and equipment-related factors on the computed tomography (CT) dose received by patients from positron ...emission tomography-CT (PET-CT) using system-generated dose-length product (DLP) values and also to check the effective dose (ED) received from various CT protocols at our institute. Materials and Methods: This retrospective study included 78 adult patients who underwent F-18 fluorodeoxyglucose whole-body PET-CT and were divided into three groups based on the area of primary cancerous lesion. In Group A, we had 44 patients who underwent PET-CT (head-and-neck protocol), in Group B, we had 24 patients who underwent PET-CT (whole body with brain protocol), and in Group C, we had 10 patients who underwent PET-CT (pelvis protocol). All of the patients under the study are of South Asian ethnicity. A majority of patients 53.85% were males and remaining 46.15% were females. The product of conversion factor (k-coefficient), as described in "American Association of Physicists in Medicine Report No. 96" and DLP value generated by the scanner, was used to calculate the ED. Moreover, we also performed regression analysis to check relation between body weight, height, scan range, tube current, Volume computed tomography dose index (CTDIvol), DLP, and ED. Results: The regression analysis shows that scan range, patient height, weight, tube current, and DLP were significantly correlated with ED (P < 0.05 for all). Moreover, the DLP and conversion factor method estimated the ED from various groups. Patients under Group A (head-and-neck protocol), Group B (whole body with brain protocol), Group C (pelvis protocol) received an average ED of 22.45 mSv, 22.40 mSv, and 21.24 mSv, respectively. Conclusion: ED from CT component of PET-CT can be assessed as the product of scanner-generated DLP and conversion factor for selected range. Moreover, body weight, scan range, and tube current had an independent significant effect on ED received from CT.
The aim of this article is to assess Tamil Nadu pediatric computed tomography (CT) diagnostic reference levels (DRLs) by collecting radiation dose data for the most commonly performed CT ...examinations. This work was performed for thirty CT scanners installed in various parts of the Tamil Nadu region. The patient cohort was divided into two age groups: <1 year, and 1-5 years. CT dose indices were measured using a 10 cm
pencil ion chamber with pediatric head and body polymethyl methacrylate phantoms. Dose data such as volumetric CT dose index (CTDI
) and dose length product (DLP) on a minimum of twenty average-sized pediatric patients in each category were recorded to calculate a mean site CTDI
and DLP value. The rounded 75
percentile was used to calculate a pediatric DRL for each hospital, and then region by compiling all results. Data were collected for 3600 pediatric patients. Pediatric CT DRL for two age groups: <1 year (CTDI
and DLP of head 20 mGy, 352 mGy.cm, chest 7 mGy, 120 mGy.cm and abdomen 12 mGy, 252 mGy.cm), and 1-5 years (CTDI
and DLP of head 38 mGy, 505 mGy.cm, chest 8 mGy, 132 mGy.cm and abdomen 14 mGy, 270 mGy.cm) for select procedures have been calculated. Proposed pediatric DRLs of CTDI
and DLP for head procedure were lower, and for chest and abdomen procedures were higher than European pediatric DRLs for both age groups.
Purpose:
The extensive use of multislice computed tomography (MSCT) and the associated increase in patient dose calls for an accurate dose evaluation technique. Optically stimulated luminescence ...(OSL) dosimetry provides a potential solution to the arising concerns over patient dose. This study was intended to evaluate the feasibility and accuracy of OSL dosimeter systems in the diagnostic CT x-ray beam energy range.
Methods:
MSCT dose profiles were measured by irradiating OSL strips placed inside the extended PMMA head and body phantoms at different scan conditions by varying kVp settings (100, 120, and 140 kVp) and collimated beam widths (5, 10, 20, and 40 mm). All scans in this study were performed using a GE Lightspeed VCT scanner in axial mode. The exposed strips were then read out using a custom-made OSL strip reader and corrected with field-specific conversion factors. Based on the corrected OSL dose profile, the
CTDI
450
-OSL
and
CTDI
100
-OSL
were evaluated.
CTDI
100
-IC
was also obtained using a 100 mm long pencil ionization chamber for accuracy verification.
CTDI
100
-efficiency
can be further evaluated by calculating the ratio of
CTDI
100
-OSL
and
CTDI
450
-OSL
, which was compared to results from previous studies as well.
Results:
The OSL detectors were found to have good sensitivity and dose response over a wide range of diagnostic CT x-ray beam energy viz. the primary beam and the scatter tail section of the dose profile. The differences between
CTDI
100
values obtained using the OSL strips and those obtained with 100 mm long pencil ionization chamber were
<
±
5
%
for all scan conditions, indicating good accuracy of the OSL system. It was also found that the
CTDI
100
-efficiency
did not significantly change as the beam width increased and tube voltage changed. The average
CTDI
100
-efficiency
at the center of the head and body phantoms were 72.6% and 56.2%, respectively. The corresponding values for the periphery of the head and body phantoms were 85.0% and 81.7%. These results agreed very well with previous results from the literature using other detection techniques or Monte Carlo simulations.
Conclusions:
The LED-based OSL system can be an accurate alternative device for CT dose evaluations.
CTDI
100
measurement with the use of a 100 mm pencil ionization chamber substantially underestimates the
CTDI
∞
value even with 5 mm collimated beam width. The established complete set of
CTDI
100
-efficiency
correction factors for various scan parameters allows for accurately estimating
CTDI
∞
with the current use of pencil chamber and dose phantoms. Combined with the simple calibration, it gives this work great potential to be used not only in routine clinical quality assurance checks but also as a promising tool for patient organ dose assessment.
Background: Nowadays, the use of computed tomography (CT) as a diagnostic tool has been considerably increased. Therefore, implementation of the program to conform the protection regulations on the ...CT scan is necessary to reduce the detrimental effects of radiation.
Objective: This study was performed to measure weighted CT dose index (CTDIW) and dose length product (DLP) in routine CT protocols of the adult patients.
Methods: In this study, the patient dose was determined in routine CT protocols. The CT scanner used in this study was a single-slice Toshiba model. Scan parameters for each protocol were registered for 10 standard sized patients and then by applying it to the CT system, CTDIw and DLP mean values were calculated and finally the values of dose were compared with the reference dose limit.
Results: The mean values of CTDIw and DLP for head, para nasal sinuses, chest, abdomen, and pelvis protocols were 34.11, 19.67, 15.47, 13.95, 10.08 mGy and 362.67, 153.97, 307.33, 346.07, 189.37 mGy.cm, respectively. The mean values of CTDIW and DLP obtained in all of the protocols were less and even less than half in some of the protocols compared with the European guidelines and the UK reference values. However, mean values of CTDIw in the Chest and Abdomen protocols, were greater than IAEA reported values.
Conclusions: Using lower milli Amperes and higher kilo voltage peak as well as minimizing scan area and number of slices should be considered for more reduction in patients' dose.
Cone beam computed tomography (CBCT) systems are fitted to radiotherapy linear accelerators and used for patient positioning prior to treatment by image guided radiotherapy (IGRT). Radiotherapists' ...and radiographers' knowledge of doses to organs from CBCT imaging is limited. The weighted CT dose index for a reference beam of width 20 mm (CTDIw,ref) is displayed on Varian CBCT imaging equipment known as an On-Board Imager (OBI) linked to the Truebeam linear accelerator. This has the potential to provide an indication of organ doses. This knowledge would be helpful for guidance of radiotherapy clinicians preparing treatments. Monte Carlo simulations of imaging protocols for head, thorax and pelvic scans have been performed using EGSnrc/BEAMnrc, EGSnrc/DOSXYZnrc, and ICRP reference computational male and female phantoms to derive the mean absorbed doses to organs and tissues, which have been compared with values for the CTDIw,ref displayed on the CBCT scanner console. Substantial variations in dose were observed between male and female phantoms. Nevertheless, the CTDIw,ref gave doses within ±21% for the stomach and liver in thorax scans and 2 × CTDIw,ref can be used as a measure of doses to breast, lung and oesophagus. The CTDIw,ref could provide indications of doses to the brain for head scans, and the colon for pelvic scans. It is proposed that knowledge of the link between CTDIw for CBCT should be promoted and included in the training of radiotherapy staff.
Purpose: The purpose of this study is to compare computed tomography (CT) radiation dose measurement methods proposed by TG111, International Electrotechnical Commission (IEC), and a direct dose ...profile integral (DPI) measurement method. Methods: Pencil and Farmer ion chambers are used for integrating dose profiles at different beam widths in a 60 cm long body phantom. Resulting DPI is used to calculate CT dose index (CTDI) at each beam width. Measurements are also done for a pencil chamber inserted into a 15 cm body phantom at the reference beam width. The reference measurement is scaled with pencil chamber measurements in air at different beam widths, according to the IEC approach. Finally, point dose measurements are done with a Farmer chamber under equilibrium conditions according to the TG111 method. All CTDIs calculated from measured data are compared to the scanner displayed CTDIs. Results: Calculated CTDIs, at different beam widths, using the IEC approach are within 20% of CTDIs calculated from DPI measurements in a 60 cm long body phantom. Dose Length Integral (DLI) obtained from TG111 method is close to the results obtained from DPI measurements. Scanner displayed CTDIs are lower than all measured values by up to 38% at the techniques used. Conclusion: Although the IEC method is the easiest to use compared to the TG111 and direct DPI measurement method, it underestimates dose indices by about 20%. CTDIs displayed on the GE scanner are lower than those measured in this study by up to 38%.
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