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NCICT User Manual

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NCI Dose Team edited this page May 3, 2026 · 43 revisions

NCICT4.20260502

NCI Dosimetry System for Computed Tomography

Introduction

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 the following steps:

  1. Patient characteristics definition
  2. Scanner parameters
  3. Scan coverage definition
  4. Organ and effective dose output
  5. Batch calculation mode

1. Patient Characteristics

NCICT supports three phantom libraries to accurately match patient anatomy and body dimensions:

  1. ICRP reference pediatric and adult phantoms (n=12)
  2. Body size–dependent pediatric and adult phantoms (n=360)
  3. Pregnant women and fetal phantoms at 8, 10, 15, 20, 25, 30, 35, and 38 weeks of gestation

1.1 Age-based selection: ICRP reference phantoms

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 ICRP phantoms are selected, reference height and weight are automatically assigned.

If a patient’s age falls between reference groups, users may interpolate organ doses or select the nearest reference age group.

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1.2 Height- and weight-based selection: size-dependent phantom library

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 size-dependent phantom. Phantom height and weight can be adjusted using the + and − buttons.

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Alternatively, users can click the "Phantom Height Weight Map" button to access an interactive size map. Blue cells representing height and weight can be selected and will be reflected in the main panel.

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1.3 Fetus models

When fetal organ doses are of interest, users can select the "Fetus" tab and specify fetal age (8–38 weeks). Because fetal age may not directly correspond to maternal abdominal diameter, the maximum maternal abdominal diameter (cm) is also displayed to assist in selecting the most appropriate phantom.

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1.4 Pregnant women phantoms

When maternal organ doses are of interest, fetal age (or maternal abdominal diameter) can be selected under the "Mother" tab.

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2. Scanner Parameters

Two scanner parameter scenarios are supported.

2.1 CTDIvol unavailable

When CTDIvol is not available, it can be reconstructed using scanner model, tube potential (kVp), current (mA), rotation time (sec), pitch, and total collimation (mm). CTDIvol (mGy) is automatically calculated using a built-in normalized CTDIw (mGy/mAs) library (Lee et al., 2014) for over 160 scanner models.

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A generic longitudinal tube current modulation (TCM) model is implemented for illustrative purposes. It is not vendor-specific. TCM strength ranges from 0 (no modulation) to 1 (maximum modulation). The modulated current profile is displayed next to the phantom panel.

2.2 CTDIvol available

Users may directly enter CTDIvol and CTDI phantom type. This value overrides all other scanner parameters. NCICT uses a scanner-independent algorithm, so CTDIvol drives organ dose estimation even when a specific scanner model is not listed.

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2.3 CT-related Dose Metrics

  • DLP is calculated from CTDIvol and scan length
  • WED (cm) is derived from voxel phantom data
  • SSDE is calculated using regression equations based on WED
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3. Scan Coverage Definition

Scan coverage can be defined:

  • interactively (mouse drag)
  • numerically (Scan Start cm / Scan End cm)
  • using predefined protocols

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4. Dose Output

NCICT reports organ absorbed dose (mGy) and effective dose (mSv). Results are intended for comparative and population-level analyses, not individual risk estimation.

Detailed cardiac substructure doses are available when size-dependent phantoms are selected.

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Cardiac Substructure Acronyms

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 Ventricular 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

5. Batch Calculation Mode

Input parameters can be provided in CSV format. A template file (ncictBatchInput.csv) is available in the repository and can be edited in Excel.

The Batch CSV uses the same calculation parameters as the NCICT API. The API uses JSON format and GUI Batch uses CSV format, but the parameter names and meanings are the same.

Required Batch CSV column order:

dose_target, age, sex, height, weight, wed, start, end, kvp, tcm_strength, head_body, ctdivol, custom_ma

Additional empty columns may be placed after custom_ma to enter slice-specific custom mA values across Excel cells.

Parameters Note
dose_target patient, fetus, or mother
age Patient age in years for patient; gestational age such as 8wk, 30wk, or 38wk for fetus and mother
sex f or m for patient; leave blank for fetus and mother
height Patient height in cm; optional
weight Patient weight in kg; optional
wed Water equivalent diameter in cm; optional
start Scan start location from the top of the head in cm, or landmark ID
end Scan end location from the top of the head in cm, or landmark ID
kvp Tube potential
tcm_strength TCM strength from 0 to 1; use -1 for custom mA values
head_body 1=16 cm CTDI phantom, 2=32 cm CTDI phantom
ctdivol CTDIvol in mGy
custom_ma Required when tcm_strength = -1; enter the first custom mA value here

If a patientID column is included, NCICT uses it in the output. If patientID is omitted, rows are numbered automatically.

NCICT matches the closest phantom based on age, sex, height, weight, and WED when those values are provided.

For patient, NCICT automatically selects the pediatric or adult phantom group using age and sex. Age < 20 is treated as pediatric. For fetus and mother, enter gestational age using week text such as 8wk, 10wk, 15wk, 20wk, 25wk, 30wk, 35wk, or 38wk.

start and end may be scan positions in cm or landmark IDs. If one value is a landmark ID, the other must also be a landmark ID.

When editing the Batch CSV in Excel, custom mA values can be entered across multiple cells starting at the custom_ma column:

dose_target age sex height weight wed start end kvp tcm_strength head_body ctdivol custom_ma
patient 10 f 25 0 20 120 -1 1 20 100 200 300 400 500 600 700

Do not add commas, brackets, or quotation marks when entering custom mA values across Excel cells. NCICT reads the custom_ma cell and all numeric cells to its right as one custom mA profile. Leave these cells blank when tcm_strength is not -1.

Example Batch CSV rows:

dose_target,age,sex,height,weight,wed,start,end,kvp,tcm_strength,head_body,ctdivol,custom_ma,,,,,,
patient,10,f,150,50,20,0,20,120,0,1,20,,,,,,,
patient,10,f,,,25,0,20,120,-1,1,20,100,200,300,400,500,600,700
fetus,38wk,,,,,1004,1009,120,0,2,20,,,,,,,
mother,30wk,,,,,1004,1009,120,0,2,20,,,,,,,

Output CSV includes:

  • Patient ID
  • Dose Target
  • Age, sex, height, weight, WED, and scan start/end
  • Scanner parameters
  • Matched phantom group and matched phantom size or fetal age
  • Organ doses and effective dose

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