The National Cancer Institute Dosimetry System for Computed Tomography (NCICT) is a software application designed to estimate radiation doses absorbed by organs and the effective dose for individuals undergoing CT scans. The program is based on a comprehensive database of organ dose conversion coefficients pre-calculated using Monte Carlo radiation transport simulations and multiple computational human phantom models in combination with a reference CT scanner. Organ dose calculations are performed in four steps: entering patient characteristics, specifying scanner parameters, defining scan coverage, and obtaining the organ and effective dose outputs. The Batch Calculation mode enables automated dose measurements.

To estimate organ doses, it is crucial to input the details of the patient. Body size is a key factor influencing organ doses in CT scans, but this information is not always available. In such cases, age and corresponding body size can be used as alternatives. Users can select the patient’s age from one of five age groups: newborn, 1 year, 5 years, 10 years, 15 years, or adult (assumed to be over 20 years). Once the age is selected, the reference height and weight defined by the International Commission on Radiological Protection (ICRP) will be displayed (non-editable).

If the patient’s age does not match the ICRP age groups, users can:

1. Interpolate organ doses calculated for the younger and older age groups (e.g., interpolate doses from 1-year and 5-year phantoms for a 3-year-old patient), or
2. Select the age group closest to the patient’s age (e.g., choose the 5-year group for a 4-year-old patient).

Another scenario arises when the patient’s height and weight are available. In this case, users can disregard age and directly use height and weight for more accurate dose calculations. Users should first select the Age Group as either Pediatric or Adult, then choose the patient’s gender. Within the selected age group, users can specify height and weight by referring to phantom maps, which can be viewed in a separate window by clicking the Show Phantom Height Weight Map button. The height and weight distribution aligns with the body size-dependent phantom library.

Users can select the Fetus tab to calculate fetal organ doses or the Mother tab to calculate organ doses for pregnant women. Eight gestational age options are available for both the fetus and the pregnant woman.

The next step requires users to input the technical parameters of the CT scanner. There are two scenarios: when CTDI_vol is known or unknown. If CTDI_vol is available (usually found on the dose or protocol page after the scan), users will also need to specify the CTDI phantom type (16 cm head phantom or 32 cm body phantom) and the tube potential (kVp) associated with the CTDI_vol. Users should select the appropriate head or body filter, input the CTDI_vol, and proceed to the next step, Scan Range. If a custom CTDI_vol is entered, it will be displayed in blue as Custom CTDI_vol (mGy).

When CTDI_vol is not available, typically in dose reconstruction for older CT scanners, users will need to reconstruct CTDI_vol using the available parameters. First, users should select the manufacturer and model of the CT scanner from the dropdown menu. Next, they should choose the type of CTDI phantom (head or body). Then, users need to input the tube potential (kVp), current-time product (mAs), pitch, and total collimation (mm). NCICT will then display the normalized CTDIw (mGy/mAs) from a built-in nCTDIw library, and CTDI_vol will be derived using these parameters and displayed.

Tube current modulation strength can be selected among 0.0, 0.25, 0.5, 0.75, and 1.0, which will create a generic modulation curve based on a previously published algorithm. Please note that the algorithm is a generic model not specific to a certain scanner vendor or model. You can also define current limit (default is 600 mA) to limit the modulated mA. Average CTDI_vol (mGy) (in blue color) will be automatically calculated by implementing slice-specific modulated CTDI_vol.

The Effective Diameter (cm) will be displayed at the bottom, along with the two dose descriptors: Dose-Length Product (DLP) and Size Specific Dose Estimates (SSDE).

Scan coverage (start and end locations) must be defined on the selected phantom, with three available options. First, users can drag the red box on the phantom's frontal and rear views using the cursor to adjust the scan locations. The second option is to directly enter the scan start and scan end locations in the two boxes at the bottom. These values represent the distance from the top of the phantom (e.g., a scan start of 10 cm means the scan begins 10 cm from the top of the head). Once entered, the red box will automatically adjust to the specified locations. The third option is to select a protocol from the "Predefined Protocol" menu, which is based on protocols used at the National Institutes of Health Clinical Center. There are seven scan protocols: head, neck, chest, abdomen, pelvis, abdomen-pelvis (AP), and chest-abdomen-pelvis (CAP). When a protocol is selected, the red box on the phantom is automatically adjusted. The scan coverage will also automatically adjust based on anatomical landmarks when the phantom selection is changed.

Once all the steps above are completed, the organ absorbed doses (mGy) and effective dose (mSv) will be displayed in the table on the right. The resulting doses are automatically copied to the clipboard, allowing them to be pasted into other documents such as Microsoft Word, Excel, etc.

The organ names can be copied from the table by selecting the column with the mouse. The table includes all organs for which tissue weighting factors from ICRP Publication 103 are defined. Depending on the phantom's gender, organs of the opposite gender will have a zero dose (e.g., the dose to the prostate and testes will be zero for female phantoms). Active and shallow marrow (formerly referred to as bone surface in the ICRP definition) doses are calculated based on fluence passing through the spongiosa region of the skeleton, combined with a dose response function derived from Monte Carlo simulations of detailed spongiosa structure models. It should also be noted that gender-specific organ doses need to be averaged across male and female phantoms to derive the effective dose, as defined by ICRP Publication 103. The effective dose calculated for a male or female patient is a gender-specific quantity that can be used for comparing doses by protocol, hospital, scanner, etc.

When the dose to a large number of patients is of interest, users can utilize the Batch Calculation feature. Patient- and scanner-related parameters can be listed in a CSV-formatted file, following the header in the first row. The NCICT folder contains an example batch file, ncict_batch_input.csv, as shown below.

Patient ID	Scan Start	Scan End	Phantom Group	Height	Weight	kVp	TCM strength	CTDI phantom	Average CTDIvol
1	1	14	1	85	10	80	0	1	12
2	1	14	1	85	10	100	0.25	1	12
3	23	39	2	115	15	80	0	1	10
4	23	39	2	115	15	100	0.25	1	12
5	43	81	3	150	40	100	0	1	20

• Patient ID: numerical ID number for patients
• Scan Start: the distance (cm) of scan start from the top of the phantom's head
• Scan End: the distance (cm) of scan end from the top of the phantom's head
• Phantom Group: 1-pediatric female,2-pediatric male,3-adult female,4-adult male,5-fetus,6-pregnant woman
• Height: height of the patient in cm
• Weight: weight of the patient in cm
• kVp: tube potential
• TCM strength: number ranging from 0 (no TCM) to 1 (100% TCM)
• CTDI phantom: 1-16 cm CTDI phantom, 2-32 cm CTDI phantom
• CTDI_vol: volumetric CTDIw

If users select Phantom Group 5 (fetus) or 6 (pregnant women), the height should be set to 164 (the reference height for an adult female), and the weight should correspond to the gestational age (8, 10, 15, 20, 25, 30, 35, 38 weeks). For example, if users intend to compute the organ doses for a 35-week fetus or a pregnant woman at 20 weeks of pregnancy, they would use the following information: for the fetus, the phantom group is 5, height is 146, and weight is 35; for the pregnant woman, the phantom group is 6, height is 164, and weight is 20.

By clicking Read Batch Input under the Batch Run menu, NCICT will import the input file and export the output organ doses. Batch Calculation is applicable when users have their own CTDI_vol.

• Non-Commercial Research Use There is no charge to use these resources for non-commercial research purposes. Please click Software Transfer Agreement form, fill out the form in your web browser*, save it to your computer, then obtain the signatures and submit it to Dr. Choonsik Lee.
• Commercial Use Contact Dr. Kevin Chang of the NCI Technology Transfer Center to discuss accessing the free trial version and the licensing process for commercial use.