Medical Imaging Radiation Shielding Calculator
Published: Aug 09, 2026
Source: Ionactive Radiation Protection Resource
Prelim
This Ionactive calculator is useful for medical imaging facilities which can require very different levels of structural radiation shielding depending on the equipment, workload, room geometry and occupancy of surrounding areas. In some ways this shielding design is potentially more complicated than the higher energy medical facilities using linear accelerators etc. Our calculator provides a practical way to explore requirements for a wide range of diagnostic imaging applications, including general radiography, fluoroscopy, interventional procedures, mammography, CT, mobile C-arm fluoroscopy and dental CBCT.
The calculation methods are based principally on NCRP Report No. 147, supplemented where appropriate by later British Institute of Radiology (BIR) methodology and published work from recognised specialists in diagnostic radiation shielding. The calculator allows site-specific workloads, distances, occupancy factors, design goals, existing barriers and shielding materials to be considered, while published worked examples and an extensive internal validation process provide useful reference points for checking and understanding the results.
The calculator is intended as a design, assessment and educational aid. Final shielding specifications should be reviewed in the context of the actual installation and by a suitably qualified Radiation Protection Adviser (RPA).
Note: if you are only interested in the instantaneous dose rate (IDR) of a X-ray beam of a given kVp through shielding, then you may wish to explore the a simpler calculator here: Diagnostic X-ray Shielding / Transmission Calculator (this calculator alone cannot be used to design shielding for a medical imaging facility).
Medical Imaging Radiation Shielding Calculator
Structural radiation shielding estimates for medical imaging using recognised NCRP 147 and selected BIR methods.
Calculation inputs
This text does not affect the calculation. It is carried into the displayed and copied result so an individual barrier remains identifiable.
Selected-material result
All-material comparison
The same modality, barrier assessment, workload, geometry, design goal, equipment preshielding choice and existing structural barrier are applied to each proposed material.
| Proposed material | Total requirement | Equipment credit equivalent | Existing structural equivalent | Total credited equivalent | Additional calculated | Practical output | NCRP range / fit check |
|---|
Calculation derivation — full checking precision
Formal advice
If you need formal advice on calculating shielding requirements for medical diagnostic facilities, then head over to our Radiation Protection Adviser (RPA) services , or try our online radiation protection training courses for in-depth study of x-ray and gamma shielding materials and techniques.
Release notes
Version V1 (August 2026). The Ionactive Medical Imaging Radiation Shielding Calculator is intended to be useful as a practical shielding design tool, and as a way of understanding how different factors in a shielding assessment interact. Our calculator therefore provides more than a single shielding thickness: it allows underlying assumptions, the source term, geometry and resulting transmission requirement to be examined. It encourages the use to ask 'what if' type questions.
Published examples and presets
For a number of modalities the calculator includes published worked examples and reference presets. These allow recognised NCRP and BIR examples to be loaded directly into the calculator and reproduced using the same calculation engine as a normal user assessment.
Presets are particularly useful for learning the methodology, checking that the calculator is behaving as expected, and exploring the effect of changing individual parameters. They should not, however, be treated as confirmed design values for a real installation. Actual equipment, workload, room geometry and occupancy should be used whenever these are available. If you have your own in-house calculator (e.g. NCRP 147 spreadsheet), you can compare the two by using our presets.
Summary or detailed results
Results can be viewed either as a simplified summary or as a more detailed technical analysis.
The summary view concentrates on the shielding requirement and practical specification. The detailed view exposes more of the calculation, including the source radiation significance, distance correction, occupancy and design-goals, required barrier transmission and the calculated shielding thickness.
This means that a user who simply wants to explore a design option can obtain a clear result without having to work through every intermediate quantity, while a medical physicist, RPA or student can examine how that result has been derived. The user can use the copy summary button to copy and paste the results into a document or spreadsheet.
Distance treatment
Distance is one of the most influential parameters in any shielding calculation, so the calculator makes the distance convention explicit rather than hiding it within the calculation.
Where appropriate, the user can enter the distance directly to the point at which the shielding design criterion is to be assessed. For calculations following the NCRP wall convention, the calculator can also apply an additional 0.3 m beyond the barrier surface used to represent the location of a person outside the room.
For example, a source-to-wall distance of 3.0 m using this NCRP convention gives a calculation distance of 3.3 m.
The distance actually used in the shielding calculation is shown in the result so that the geometry can be checked easily.
[Ionactive comment: We tend to find working with architects and end users during critical examinations, that most (at least in the UK) prefer working at the surface of the shield and the 0.3m NCRP offset is not often accounted for. This calculator allows you to take measurements directly off a plan, enter into the calculator and then decide if the calculation should include the addition offset.]
Air kerma and dose-rate units
Diagnostic X-ray shielding calculations are normally performed using air kerma, expressed in units such as µGy, mGy or Gy. This is why our calculator uses air kerma for source terms, weekly design goals and calculated radiation levels.
Radiation protection instruments and personal dosimetry commonly read in µSv/h, μSv or mSv, so it is natural to want to compare the two.
For diagnostic X-ray radiation, a value expressed in µGy and a radiation-protection quantity expressed in µSv will often be of the same general order of magnitude, which makes a rough comparison useful when reviewing survey-meter readings. They are not, however, physically identical quantities and should not automatically be treated as interchangeable. The relationship depends on factors including photon energy, radiation geometry and the response and calibration of the measuring instrument.
For a formal shielding assessment, the air-kerma quantities used by the published shielding methodology therefore remain the basis of calculation. A radiation survey meter reading in µSv/h can provide useful practical context, but the instrument and measurement conditions should be understood. In many of the modalities included with the calculator, instantaneous dose rate is not a practical measurable quantity.
How was the calculation made?
At the end of the detailed results section the calculator presents the calculation process and method used (if calculation derivation is clicked) This is included so that more experienced users can check (or challenge!) the calculation , not simply accept the answer given. This is also useful for training purposes.
Depending on the selected modality, the calculation may use NCRP workload distributions, KAP or DLP-based scatter methods, measured or published secondary-radiation source terms, inverse-square distance correction, occupancy and shielding design goals, followed by published transmission data to determine the required barrier thickness.
The final result provides both the calculated continuous thickness and, where appropriate, a practical shielding specification such as a recognised lead code. Existing barriers can also be included so that the calculator can assess the additional shielding required rather than assuming an entirely new barrier. This is especially useful for architects who are designing new medical facilities into existing buildings with existing walls, floors and partitions.
How to use the calculator
Our calculator is designed to assess one barrier at a time. In most cases, the user first selects the imaging modality, then enters the workload, geometry and shielding design criteria relevant to the wall, floor, ceiling or other barrier being assessed. Whilst results cannot be saved in version V1, the user can name the barrier and then copy the results over to another document / spreadsheet. Using this approach the calculator can be used to assess each barrier in turn, for example as annotated on an architects plan.
For a typical calculation, the user will:
- Select the imaging modality. Examples include general radiography, fluoroscopy, CT, mobile C-arm fluoroscopy, mammography and dental CBCT.
- Describe the barrier being assessed. An optional barrier reference or description can be entered, such as Wall W2 — primary wall adjacent to corridor or Ceiling C1 — office above.
- Enter the workload or source term. Depending on the modality, this may be expressed in procedures per week, KAP, DLP, or another published source term such as air kerma per examination or per scan at 1 m.
- Enter the geometry. The user defines the appropriate distance from the radiation source, patient or scatter point to the location beyond the barrier where the shielding design goal is to be met.
- Enter the shielding design criteria. This normally includes the occupancy factor for the area beyond the barrier and the weekly design goal in air kerma.
- Select the shielding material. The calculator then determines the continuous shielding thickness required, and where appropriate also gives a practical lead specification or lead code.
- Include any existing barrier. Where a wall, floor, ceiling or equipment already provides potential shielding, this can be included so that the calculator estimates the additional shielding required.
The result can be viewed either in a summary format or in a more detailed technical form showing the steps and assumptions used.
Basic principles of the shielding calculation
Although the exact method varies between modalities, most shielding calculations are based on the same general ideas. We only include the basics here, if you want the fullest explanation and all the data tables then consider reading this resource : NCRP 147 'Structural Shielding Design for Medical X-Ray Imaging Facilities'.
1. Radiation source or workload
The first step is to estimate how much radiation is incident on the barrier before any shielding is applied. This depends on the type of imaging equipment and the way it is used.
For example:
- a general radiographic room may use published per-patient source terms,
- a mobile C-arm may use KAP-based scatter factors,
- CT may use DLP-based workload methods,
- dental CBCT may use air kerma per scan at 1 m.
The calculator uses recognised published methods for these source terms, principally from NCRP 147 and later BIR-based approaches where appropriate.
2. Distance
The level of radiation reaching the barrier or assessment point depends strongly on distance. In general, radiation intensity falls with increasing distance, approximately according to the inverse square law.
Where appropriate, the calculator allows either:
- a direct distance to the assessment point, or
- a wall-surface distance with the NCRP convention of
- assessing the dose at a point 0.3 m beyond the barrier.
The actual distance used in the calculation is shown in the output so that the user can confirm the geometry. In most cases it is the dose at a distance that is being calculated, rather than dose rate.
3. Occupancy and design goal
Shielding is not designed simply to reduce the radiation level as much as possible; it is designed so that the radiation level in the occupied area beyond the barrier does not exceed the chosen design goal.
This depends on:
- the weekly shielding design goal, and
- the occupancy factor, which represents how much of the working week the adjacent area is occupied.
In the UK for completely undesignated areas, a design goal will likely be 6 μSv/week (0.3 mSv/year) but ALARP (as low as reasonably practicable) must also be accounted for. These are combined in the usual way to determine the tolerable transmission through the barrier.
4. Barrier transmission and shielding thickness
Once the required transmission is known, the calculator uses published transmission data for materials such as lead, concrete, gypsum, steel and others, depending on modality and method.
The result is a calculated continuous thickness. Where lead is used, the calculator may also suggest a practical lead specification or lead code, because real shielding is normally installed in standard available thicknesses rather than arbitrary fractions of a millimetre. Upscaling to the next available lead code helps to further optimise the performance of the barrier (a follow the ALARP principle).
5. Existing shielding
If a barrier already exists, or if equipment such as a bucky or receptor assembly provides verified attenuation, the calculator can include this so that the result represents the additional shielding required, not simply the total shielding needed from zero. If this is included the calculator asks the user to verify the specification of the shielding before being included in the calculation process.
Understanding the calculator output
The calculator usually provides more than a single thickness value. Depending on the modality and the chosen output mode, the result may include:
- the unshielded weekly air kerma at the barrier or assessment point,
- the required barrier transmission,
- the calculated continuous shielding thickness,
- a practical lead-code specification,
- the effect of existing barrier material,
- a comparison of different shielding materials,
- and a detailed calculation breakdown (if this option is selected).
This allows the calculator to be used both as a practical design tool and as a way of understanding how the final result has been obtained.