NCICT User Manual

NCICT 3.0

NCI Dosimetry System for Computed Tomography

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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 population-based dose evaluation, benchmarking, and regulatory-facing analyses, rather than patient-specific clinical decision support.

Organ dose calculations are performed through four sequential steps:

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

A Batch Calculation mode is provided to support automated dose reconstruction for large datasets.

Intended use
NCICT is intended for reference dose estimation and comparative analyses.
It is not intended for real-time clinical dose calculation, site-specific customization, or individualized clinical decision making.

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Calculation Workflow (Overview)

Step	Description
1	Define patient age or body size
2	Specify scanner output (CTDIvol or reconstruction parameters)
3	Define scan coverage
4	Review organ and effective dose output

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1. Patient Characteristics

NCICT supports two approaches for defining patient characteristics, depending on the availability of body size information.

Age-based selection

When detailed body size information is unavailable, users may select one of the ICRP-defined reference age groups:

• Newborn
• 1, 5, 10, or 15 years
• Adult (assumed ≥20 years)

Reference height and weight corresponding to the selected age group are assigned automatically and are not user-editable.

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

View age-based selection example

Height- and weight-based selection

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.

View height–weight selection example

Pregnant patients and fetal dose

Separate tabs are provided to support fetal and maternal organ dose calculations for eight gestational ages.

View pregnancy tabs

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2. Scanner Parameters

Two scanner parameter scenarios are supported.

CTDI_vol available

Users enter CTDI_vol, CTDI phantom type, and tube potential (kVp).

View CTDI_vol input example

CTDI_vol unavailable (reconstruction)

When CTDI_vol is not available, it may be reconstructed using scanner model, tube potential (kVp), mAs, pitch, and collimation.

View CTDI_vol reconstruction example

Tube current modulation (TCM)

A vendor-neutral, generic tube current modulation (TCM) model may be applied. Average CTDI_vol is computed automatically.

View TCM settings

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3. Scan Range Definition

Scan coverage may be defined interactively, numerically, or by selecting predefined NIH clinical protocols (e.g., head, chest, abdomen).

View scan range definition

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4. Dose Output

NCICT reports organ absorbed doses (mGy) and effective dose (mSv). Results are appropriate for comparative and population-level analyses, rather than individual risk estimation.

View dose output table

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Batch Calculation Mode

Batch mode supports automated dose calculation using CSV-formatted input files when CTDI_vol is available.