NCI Dosimetry System for Computed Tomography

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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:

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.

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

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.

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.

Separate tabs are provided to support fetal and maternal organ dose calculations for eight gestational ages. Maternal abdominal perimeter (cm) also can be used to select a phantom.

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Two scanner parameter scenarios are supported.

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

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

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