CT Radiation Dosage Calculator

CT Dose & Risk Assistant

Created by Dr. Sharad Maheshwari MD - imagingsimplified@gmail.com

For educational use & simulation, not clinically validated.

An educational tool for adult CT dosimetry: size-specific dose estimate (SSDE), reference effective dose, and population-level lifetime attributable risk (LAR) context.

Patient Information

Age (years; adult)

Reference sexFemaleMale

AP diameter (cm)

Lateral diameter (cm)

Water-equivalent diameter, Dw (cm) — optional

Use representative dimensions across the scanned volume. If Dw is entered, it is used for the SSDE size factor; otherwise, geometric effective diameter √(AP × lateral) is used as a less-specific surrogate. Dw better reflects attenuation when reliably measured from CT image/localizer data. [1,2]

Scanner Dose Report

Scan regionHeadNeckChestAbdomen-PelvisTrunk

CTDIvol reference phantom32-cm PMMA (Body)16-cm PMMA (Head)

CTDIvol (mGy)

Total DLP (mGy·cm)

DLP-to-E coefficientICRP 103 / Deak 2010ICRP 60 / AAPM 96

LAR endpointAll-solid-cancer incidence (proxy)All-solid-cancer mortality (proxy)

What the dose measures mean

• CTDIvol (mGy): scanner-output index measured relative to a standard CT dosimetry phantom; it is not the patient's individual absorbed dose.
• SSDE (mGy): CTDIvol multiplied by a patient-size conversion factor. It improves interpretation of dose by accounting for patient size and approximates dose to the scanned region; it is not an organ dose and should not be converted to effective dose using the DLP coefficient. [1,2]
• Effective dose, E (mSv): a tissue-weighted protection quantity, estimated here from DLP × a region-specific coefficient. It supports broad comparisons and protocol-level radiation-protection discussions, not individualized retrospective risk prediction. [3,4]
• LAR display: a coarse, model-based population illustration derived from age/sex risk tables and the effective-dose estimate. It is not a validated patient-specific cancer-risk calculator. Individual risk estimation would require an appropriate organ-dose/risk model and explicit assumptions. [5]

Why the units differ: SSDE is an estimate of absorbed dose, expressed in gray units (mGy). Effective dose combines organ/tissue equivalent doses using tissue-weighting factors and is expressed in sievert units (mSv). They describe different quantities and are not interchangeable. [2,3]

References and technical basis

1. American Association of Physicists in Medicine (AAPM). Report 204: Size-Specific Dose Estimates (SSDE) in Pediatric and Adult Body CT Examinations. 2011.
2. AAPM. Report 220: Use of Water Equivalent Diameter for Calculating Patient Size and SSDE in CT. 2014.
3. International Commission on Radiological Protection (ICRP). Publication 103: The 2007 Recommendations of the ICRP. 2007.
4. AAPM. Report 96: The Measurement, Reporting, and Management of Radiation Dose in CT. 2008.
5. National Research Council. Health Risks from Exposure to Low Levels of Ionizing Radiation: BEIR VII Phase 2. 2006.

Method limitation: SSDE conversion factors depend on the CTDIvol reference phantom and patient-size metric. AAPM TG-220 clarifies that the size variable underlying the conversion-factor fit is water-equivalent diameter (Dw); geometric effective diameter is a less-specific surrogate. The 8–40 cm warning band in this prototype is a conservative software guardrail, not a formal universal AAPM validity limit. Validate region- and phantom-specific calculations before clinical use. [1,2]

Clinical and methodological limitations

• SSDE uses an exponential size-conversion approximation associated with AAPM Reports 204/220. The approximation uses Dw most directly; geometric effective diameter is a surrogate when Dw is unavailable. Confirm the applicable conversion method, CTDIvol phantom, and size range before interpreting results.
• Effective dose is estimated from DLP using a region-specific coefficient; it is a population-level radiation-protection quantity, not a direct measurement of individual risk.
• The LAR value is an experimental, coarse educational proxy. BEIR VII risk estimates depend on exposure, organ/site, age, sex, attained age and other assumptions; applying a generic effective-dose estimate does not produce a validated individual cancer-risk prediction. [5]
• This prototype is for education and research discussion, not for clinical decision-making without independent validation.

Educational prototype · Adult patients only · Verify all inputs and methodology against current professional guidance before clinical use.