NCICT User Manual
NCI Dosimetry System for Computed Tomography
The National Cancer Institute Dosimetry System for Computed Tomography (NCICT) is a reference-grade radiation dose estimation system developed by the National Cancer Institute (NCI) for estimating organ absorbed doses and effective dose associated with computed tomography (CT) examinations.
NCICT is based on pre-calculated organ dose conversion coefficients derived from Monte Carlo radiation transport simulations, multiple computational human phantom models, and a reference CT scanner framework. The system supports patient-specific dose calculations, population-based dose evaluation, and benchmarking. The program is not intended for clinical decision support.
Organ dose calculations are performed through four sequential steps:
- Patient characteristics definition
- Scanner parameters
- Scan coverage definition
- Organ and effective dose output
- Batch Calculation mode
NCICT supports three phantom libraries to accurately matching patient's anatomy and body dimensions.
- ICRP reference pediatric and adult phantoms (n=12)
- Body size-dependent pediatric and adult phantoms (n=360)
- Pregnant women and fetal phantoms at 8,10,15,20,25,30,35 and 38-week fetal ages
When detailed body size information is unavailable, users may select one of the ICRP-defined reference age groups and sex:
- Newborn male or female
- 1, 5, 10, or 15 years male or female
- Adult male or female (assumed ≥20 years)
When age and sex of the ICRP phantoms are selected, reference height and weight corresponding to a given phantom are assigned automatically.
If a patient’s age falls between reference groups, users may interpolate organ doses or select the nearest reference age group.
When patient height and weight are available, users may directly specify body size within the pediatric or adult phantom libraries. This approach maps the patient’s body size to the closest matching body size–dependent phantom. Phantom's height and weight can be adjusted using the + and - buttons next to the height and weight fields.
As an alternative and more intuitive way, users can click "Phantom Height Weight Map" button to display the interactive phantom size map. The blue cells representing height and weight can be selected which will be reflected on the main panel.
When fetal organ doses are of interest, users can select "Fetus" tab and fetal age ranging from 8 to 38 weeks. Since fetal age may not be proportional to the maternal abdominal diameter in pregnant patients, the maximum maternal abdominal diameter (cm) is also displayed next to the fetal age for users to select better matching pregnant women phantoms when diameter is available.
When pregnant women's organ doses are of interest, fetal age (or maternal abdominal diameter) can be selected from "Mother" tab.
Two scanner parameter scenarios are supported.
When CTDIvol is not available, it may be reconstructed using scanner model, tube potential (kVp), current (mA), rotation time (sec), pitch, and total collimation (mm). CTDIvol (mGy) will be automatically calculated using built-in normalized CTDIw (mGy/mAs)library (Lee et al. 2014) established for over 160 different scanner models from major manufacturers.
Generic longitudinal tube current modulation (TCM) algorithm is implemented for illustrative purposes based on slice-specific current modulation curve generated for all phantoms by z slice. It should be noted that the current TCM algorithm is not representing that of a specific vendor. TCM strength can be entered: 0 represents no modulation and 1 represents the strongest modulation. Modulated current profile is displayed next to the phantom panel. When TCM strength is greater than zero, slice-average CTDIvol is displayed in the CTDIvol field.
Users enter CTDIvol and CTDI phantom type directly to the CTDIvol field. Then the label changes to "Custom CTDIvol mGy." This value overrides other scanner parameters above. Although users' specific scanner model is not available from the Manufacturer and Model dropdown menus, the dose calculation in NCICT is based on scanner-independent algorithm so that custom CTDIvol will drive resulting organ doses.
Dose-Length Product (DLP) will be calculated and displayed based on CTDIvol (mGy) and scan length (cm). Water Equivalent Diameter (WED) (cm) will be automatically calculated using the built-in WED library derived from DICOM-CT format of all voxel phantom library. WED is calculated at the middle of scan coverage by averaging the WEDs at the scan start and end locations. Finally, Size-Specific Dose Estimate (SSDE) is calculated using regression equations combined with WED.
Scan coverage may be defined interactively using mouse drag, numerically in Scan Start cm and Scan End cm, or by selecting predefined protocols (head, neck, chest, abdomen, pelvis, abdomen-pelvis, chest-abdomen-pelvis).
NCICT reports organ absorbed doses (mGy) and effective dose (mSv). Results are appropriate for comparative and population-level analyses, rather than individual risk estimation. When size-dependent pediatric and adult phantoms are selected, detailed cardiac substructure doses will be displayed with on and off toggle icon.
Acronyms for the cardiac substructures are spelled out here:
| Acronym | Cardiac Substructure |
|---|---|
| Heart wall | Heart wall |
| H LA | Left Atrium |
| H RA | Right Atrium |
| H LV | Left Ventricle |
| H RV | Right Ventricle |
| H LVM | Left Ventricle Myocardium |
| H LMCA | Left Main Coronary Artery |
| H LADA | Left Anterior Descending Artery |
| H LCA | Left Circumflex Artery |
| H RCA | Right Coronary Artery |
| H AV | Aortic Valve |
| H MV | Mitral Valve |
| H PV | Pulmonary Valve |
| H TV | Tricuspid Valve |
A series of input parameters can be listed in csv format and NCICT can import it for batch dose calculation. A template file, ncictBatchInput.csv can be found in the NCI Dose Tools Repository where NCICT installation files are stored.
| Parameters | Note |
|---|---|
| patientID | numerical patient ID |
| scanStart cm | The distance of scan start location from the top of the patient's head |
| scanEnd cm | The distance of scan end location from the top of the patient's head |
| doseTarget | 1=pediatric female,2=pediatric male,3=adult female,4=adult male,5=fetus,6=mother |
| height cm | patient's height |
| weight kg | patient's weight |
| kVp | tube potential |
| tcmStrength | TCM strength 0-1 |
| ctdiPhantom | 1=16 cm head,2=32 cm body |
| ctdivol mGy | CTDIvol |
For doseTarget of fetus (doseTarget ID=5), the fetal age (month) must be entered to weight kg. Then pregnant woman phantom corresponding to the fetal age is selected for fetal dose calculations. The fetal age will override height.
For doseTarget of mother (doseTarget ID=6), the fetal age (month) also can be entered to weight kg. The maternal organ dose will be included to output csv file. Again this entry overrides height parameter.
NCICT will match a phantom with height, weight, or fetal age closest to the user-defined height, weight, and fetal age.
Resulting csv file includes:
- Patient ID
- Scan Start cm
- Scan End cm
- Dose Target ID
- Height cm - patient (user input)
- Height cm - phantom (phantom's height matched to user input)
- Weight cm - patient (user input)
- Weight cm - phantom (phantom's weight matched to user input)
- kVp
- TCM Strength
- Head/Body CTDI phantom
- CTDIvol mGy
- Brain, Pituitiry glands, ..... Effective Dose mSv