Projects and saved calculations — new for V2.0

Whilst the calculator can still be used for a single one-off shielding calculation, the project functions are a useful optional extra. 

For a larger shielding assessment, a project allows several independent calculations for the same imaging modality to be kept together.

For example, a project might contain separate calculations for:

• Wall W1;
• Wall W2;
• a ceiling;
• a floor;
• an adjacent corridor.

A nuclear medicine PET/PET-CT project might instead contain an uptake-room wall, scan-room wall, Hot WC assessment and other declared patient source locations.

Each saved calculation remains an independent shielding calculation. Calculations are not added or combined - they are just stored in the same project. 

Where an individual calculation contains more than one radiation source or radiation path, those source contributions are combined only within that calculation according to the geometry declared by the user. A saved calculation can be reopened, edited, duplicated or deleted.

The Project Summary provides an overview of the results from all saved calculations so that different barriers or assessment points can be reviewed together.

The Project Summary represents the last saved version of each calculation. If the currently open calculation has unsaved changes, those changes are not written into the saved project or its summary (i.e save the current calculation to update the project summary). 

Project storage and privacy

Projects are stored locally by the web browser on the device and browser profile being used. Nothing is stored by Ionactive. 

Project names, calculation inputs and saved assessment data are not sent to or stored by Ionactive because a project feature is used.

Local browser storage is intended as a convenient temporary working method, rather than a permanent archive. Browser/site data can be removed, and a project saved in one browser or profile is not automatically available on another device. For calculations that need to be retained, use Export Project and keep the exported project file stored in an appropriate local, network or cloud location. Exported project files can be imported back into the calculator. The project system is intended to help organise shielding calculations; it is not a replacement for a formally documented shielding assessment or advice from a Radiation Protection Adviser (RPA). 

Version History

Version V2.0 — August 2026

Version 2.0 extends the Ionactive Medical Imaging Radiation Shielding Calculator to include the nuclear medicine modality F-18 PET and PET/CT shielding, and introduces optional projects and saved calculations.

F-18 PET/PET-CT calculations use declared radioactive patient source locations with physical decay over the patient workflow. Multiple source paths can be considered at one assessment point, including radiation that crosses the selected target barrier and radiation arriving by a separate route. PET/CT can additionally include an independent CT workload where the CT contribution reaches the same physical target barrier. Weekly shielding and PET instantaneous dose rate constraints are assessed separately and the dominant requirement is identified.

V2.0 includes:

• a full numerical PET/PET-CT calculation derivation;
• published PET example presets;
• an Ionactive multi path worked example demonstrating an uptake room target wall together with a separately shielded Hot WC contribution (useful for understanding facility geometry);
• optional local browser projects;
• multiple named calculations within each project;
• whole project result summaries;
• project export/import;
• and local project privacy/storage information.

The optional project system allows multiple independent calculations for one imaging modality to be stored together in the user's browser. Saved calculations can be reopened, duplicated and reviewed in a whole project summary. Projects can be exported to a portable project file for backup or transfer and subsequently imported.

The established V1 diagnostic X-ray calculation methods remain available in V2.0. 

Version V1.0 — August 2026

Version 1.0 introduced the Ionactive Medical Imaging Radiation Shielding Calculator for diagnostic X-ray imaging modalities.

It was designed both as a practical shielding assessment tool and as a way of examining how workload, geometry, occupancy, design goals, barrier transmission, existing shielding and practical lead specifications interact.

Published worked examples and reference presets were included for a number of modalities so that recognised NCRP and BIR examples could be reproduced using the same calculation engine as a normal user assessment.

Summary and detailed result modes allowed either a concise design output or a more technical examination of the underlying calculation.

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' for x-ray modalities,  and AAPM Task Group 108: PET and PET/CT Shielding Requirements for PT/CT. Note that whilst these are key documents, the Ionactive calculator goes beyond these and also uses more recent data (including Ionactive in house data). 

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.
• PET/PET-CT uses radioactive-patient source terms whose activity changes with radioactive decay as the patient progresses through the clinical workflow.

The calculator uses recognised published methods for these source terms, principally from NCRP 147 and later BIR-based approaches where appropriate, and TG-108. 

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.

PET source geometry is declared directly by the user. The calculator does not infer room layout or assume that every source reaches the point through the selected target wall.

3. Occupancy and design goal

Shielding is not generally designed 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 (and is deemed ALARP). The design goal will be influenced by national standards; in the UK this would be the Ionising Radiations Regulations 2017. For the UK the design goal is rarely simply the dose limit, but rather a constraint below that. So for undesignated areas you will often see a weekly design constraint of 6 μSv/week (0.3 mSv over a working year), whereas is in NCRP 144 you will often see 20 μSv/week for the same classification of area.

Shielding will depend on:

• the weekly shielding design goal, and
• the occupancy factor, which represents how much of the working week the adjacent area is occupied.

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 (i.e. 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. 

6. PET/PET-CT source paths and time-dependent activity

PET/PET-CT extends the general shielding principles because the patient hosts a moving, decaying radioactive source rather than being next to a fixed X-ray tube / system. 

F-18 activity is integrated over each declared source period, and several source locations can contribute to one assessment point. A source can irradiate the selected target barrier or reach the assessment point by another declared path. Intermediate or alternative path shielding is treated separately from the target barrier. Therefore a contribution arriving by another path cannot be controlled by making the target barrier thicker. If the other path contribution already exceeds the selected constraints, the calculator reports that no target barrier solution exists (see the Ionactive preset 'Uptake room + Hot WC alternative path' ). 

For PET/CT, CT is treated as an independent workload and is combined with PET only where both components reach the same target barrier. The weekly combined constraint and PET IDR constraint are solved separately, with the more restrictive requirement governing the final barrier where an IDR constraint has been selected. Usually PET will dictate the shielding requirements, but this is not assumed. 

The treatment of distance

Distance is one of the most important parameters in shielding calculations, so the calculator makes the distance convention explicit rather than hiding it within the calculation.

For the diagnostic X-ray modalities the user can, where appropriate, enter the distance directly to the assessment point or use a wall surface distance with the NCRP convention of assessing a point 0.3 m beyond the barrier. The distance actually used is shown in the result.

For PET/PET-CT the user declares the distance from each radioactive patient source to the relevant target barrier or assessment point. Where a source (radiation) reaches an assessment point by another route, that source/path geometry is entered explicitly rather than inferred by the calculator.

An understanding of the calculation (derivation) process

At the end of the detailed result the calculator can display the calculation derivation. This is included so that experienced users can check, reproduce or challenge the calculation rather than simply accepting the final answer. It is also useful for training purposes where the user can follow the calculation line by line. We have avoided formatting with significant figures other than the final result, so the calculation presented is the raw data and various stages. 

Depending on modality, the calculation may use:

• NCRP workload distributions;
• KAP or DLP based scatter methods;
• published secondary radiation source terms;
• inverse square distance correction;
• occupancy and weekly design goals;
• existing barrier credit;
• and the appropriate transmission data to determine the required barrier thickness.

For F-18 PET/PET-CT the derivation additionally shows:

• radioactive patient activity basis;
• F-18 physical decay integration;
• declared source/path contributions;
• intermediate or alternative path transmission;
• target barrier solution;
• CT contribution where applicable;
• existing barrier credit;
• weekly dose constraints;
• PET instantaneous dose rate (IDR) constraints;
• and the principal shielding requirement.

Where the combined PET/PET-CT barrier exceeds the supported CT secondary transmission fit range, the CT contribution is conservatively held at the transmission corresponding to 3 mm lead or 300 mm reference density concrete, while the F-18 attenuation calculation continues normally. This avoids extrapolating the CT transmission fit beyond the range adopted by the calculator (for all x-ray imaging modalities). 

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 shows more of the calculation, including source significance, distance correction, occupancy, design goals, required transmission and calculated shielding thickness.

For PET/PET-CT the detailed output additionally shows radioactive decay, individual patient source paths, alternative path contributions, PET/CT combination and the weekly/IDR constraints (as specified). 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 an RPA, medical physicist, shielding designer or student can examine how the result has been derived.