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NCICT User Manual

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NCI Dose Team edited this page Apr 18, 2026 · 43 revisions

NCICT4.20260415

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.

Parameters Note
patientID Numerical patient ID
scanStart cm Distance from top of head
scanEnd cm Distance from top of head
doseTarget 1=pediatric female, 2=pediatric male, 3=adult female, 4=adult male, 5=fetus, 6=mother
height cm Patient height
weight kg Patient weight
kVp Tube potential
tcmStrength TCM strength (0–1)
ctdiPhantom 1=16 cm head, 2=32 cm body
ctdivol mGy CTDIvol

For fetus (doseTarget=5), fetal age (months) is entered in weight kg and overrides height.

For mother (doseTarget=6), fetal age may also be entered in weight kg.

NCICT matches the closest phantom based on input parameters.

Output CSV includes:

  • Patient ID
  • Scan Start / End
  • Dose Target
  • Patient & phantom height/weight
  • Scanner parameters
  • Organ doses and effective dose

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