Enter CT Dose Inputs
Fill the measured phantom readings and scan parameters. Results appear above this form after submission.
Example Data Table
| Parameter | Example Value | Unit |
|---|---|---|
| Center Dose | 22.4 | mGy |
| Peripheral Dose 1 | 30.1 | mGy |
| Peripheral Dose 2 | 29.8 | mGy |
| Peripheral Dose 3 | 30.6 | mGy |
| Peripheral Dose 4 | 29.9 | mGy |
| Pitch | 1.2 | — |
| Scan Length | 140 | cm |
| Tube Current | 250 | mA |
| Rotation Time | 0.5 | s |
| Collimation Width | 0.625 | mm per slice |
| Slice Count | 64 | channels |
| k-Factor | 0.014 | mSv/mGy·cm |
Formula Used
Peripheral Average = (P1 + P2 + P3 + P4) / 4
CTDIw = (1/3 × Center Dose) + (2/3 × Peripheral Average)
CTDIvol = CTDIw / Pitch
DLP = CTDIvol × Scan Length
Effective mAs = Tube Current × Rotation Time / Pitch
Total Beam Width = Collimation Width × Slice Count
Estimated Effective Dose = DLP × k-Factor
These relations are commonly used for phantom-based CT dose assessment. Actual patient dose depends on anatomy, protocol design, scanner geometry, and clinical context.
How to Use This Calculator
- Enter the center chamber dose measured in the phantom.
- Fill all four peripheral chamber readings in mGy.
- Provide pitch, scan length, tube current, and rotation time.
- Enter collimation width and the total number of active slices.
- Add the suitable conversion k-factor for the exam region.
- Press submit to display CTDIw, CTDIvol, DLP, and related outputs.
- Use the export buttons to save a CSV file or PDF report.
- Compare your results with protocol targets or reference levels.
Frequently Asked Questions
1. What does CTDI measure?
CTDI estimates scanner radiation output using standard phantoms and chamber readings. It helps compare protocols, scanners, and acquisition settings, but it does not represent exact patient organ dose.
2. Why is CTDIw different from CTDIvol?
CTDIw combines center and peripheral phantom doses into one weighted value. CTDIvol adjusts that result for pitch, making it more useful for helical scan protocol comparison.
3. What is DLP used for?
Dose length product combines CTDIvol with scan length. It is often used for exam-level dose tracking, benchmarking, and rough effective dose estimation with a region-specific conversion factor.
4. Why are four peripheral readings included?
Peripheral chamber measurements capture dose variation around the phantom edge. Averaging four positions improves stability and better represents the weighted dose distribution across the scan field.
5. Does this calculator estimate patient risk?
Not directly. It estimates technical dose indicators and a rough effective dose from DLP. Patient risk depends on age, anatomy, exam purpose, radiosensitivity, and many clinical factors.
6. What pitch value should I enter?
Enter the actual helical pitch used by the protocol. If pitch increases, CTDIvol decreases for the same CTDIw. Always confirm the scanner definition used by your system.
7. Can I use any k-factor?
Use a conversion factor suited to the body region and patient group. Head, chest, abdomen, and pediatric studies can require different values for meaningful interpretation.
8. Why include beam width and effective mAs?
These supporting outputs help review acquisition setup. Effective mAs reflects pitch-adjusted tube loading, while total beam width helps verify coverage and detector configuration assumptions.