1. Reference constraint
2. Previous radiotherapy courses
3. Radiobiology & retreatment
Result
Independent EQD2 verification
This second engine calculates each course directly in EQD2 space, applies recovery to EQD2, subtracts from the reference EQD2, then independently solves the retreatment dose from EQD2. It does not reuse the BED-to-dose solver above.
Manual EQD2.com comparison
Optimal vs mandatory / fractionation comparison
Shows all published constraints for the selected structure/metric and calculates the corresponding maximum retreatment dose using the same prior courses and α/β. This is a modelling comparison, not re-irradiation guidance.
Comparison flags
These flags apply to each reference row independently. They are not a combined Optimal-vs-Mandatory safety classification and are not clinical safety labels.
UK 2022 constraint library
Source
Diez P, Hanna GG, Aitken KL, et al. UK 2022 Consensus on Normal Tissue Dose-Volume Constraints for Oligometastatic, Primary Lung and Hepatocellular Carcinoma Stereotactic Ablative Radiotherapy. Clin Oncol (R Coll Radiol). 2022;34(5):288-300. doi:10.1016/j.clon.2022.02.010. PMID:35272913.
Model
BED = D × (1 + d/(α/β)). Residual BED for each previous course = course BED × (1 − recovery fraction). Total residual BED is the sum of all residual courses. Available BED = selected reference-constraint BED − total residual BED. The positive quadratic root gives the maximum total retreatment dose for the requested fraction count.
Important model limitations: α/β values shown as presets are modelling defaults and are not dose constraints supplied by Diez et al. Dmean, D≥xxcc minimum-spared-volume constraints, Vx constraints and report-only metrics are not converted to a scalar retreatment dose. For Dxcc hot-dose metrics, summing BED across separate plans is still only an approximation unless the same tissue volume/spatial dose distribution is demonstrated by registration and dose accumulation.
Offline use
First requirement: visit the calculator once while connected to the internet. This allows your browser to save the app files for offline use. Offline installation works when the calculator is hosted over HTTPS.
iPhone / iPad: open the calculator in Safari while online → tap Share → Add to Home Screen → Add. Launch it once from the new Home Screen icon while still online. You can then use the calculator without a network connection. If you only keep a Safari bookmark rather than adding it to the Home Screen, offline behaviour may be less reliable.
Android: open the calculator in Chrome while online → choose Install app or Add to Home screen from the browser menu → confirm installation. Launch it once while online. It can then be opened from the app icon without a network connection.
Desktop: Chrome or Edge can install the site as an app from the browser install icon/menu. Safari and Firefox can still use the website, although installation behaviour varies. Visit once online before relying on the cached offline copy.
Checking offline mode: after installation and one successful online launch, switch the device to airplane mode and reopen the calculator from its Home Screen/app icon. The calculator, constraint library and validation page should remain available. External links such as the publication DOI will still require an internet connection.
After an update: reconnect to the internet and open the calculator once. Leave it open briefly so the browser can retrieve the new release. If an old version persists, close and reopen the installed app; as a last resort remove the Home Screen app/site data and reinstall it.
Release information
Version: 1.0.1
Build date: 3 September 2026
Validation: known-answer regression tests.
Clinical governance
This is an arithmetic aid only. Review original and retreatment dose distributions, spatial overlap, registration uncertainty, DVHs, organ motion, interval, systemic therapy, organ architecture and local re-irradiation policy. Volume constraints such as V20Gy/V10Gy and spared-volume constraints cannot be reduced to a safe retreatment point dose using this model.
Validation
The release includes a known-answer regression suite that checks both internal calculation pathways against predefined cases.
Methodology and reference
Primary calculation: BED = D × (1 + d/(α/β)). Residual BED is calculated after applying the user-selected recovery percentage. Remaining BED is converted to the requested retreatment fractionation using the positive quadratic solution.
Independent check: the same courses are calculated independently in EQD2 space and converted back to the proposed fractionation. Agreement is checked numerically.
Reference constraints: Diez P, Hanna GG, Aitken KL, et al. UK 2022 Consensus on Normal Tissue Dose-Volume Constraints for Oligometastatic, Primary Lung and Hepatocellular Carcinoma Stereotactic Ablative Radiotherapy. Clin Oncol (R Coll Radiol). 2022;34(5):288-300. doi:10.1016/j.clon.2022.02.010.
Clinical-use statement
This is a radiobiological calculation aid, not an independently validated medical device and not a substitute for clinical judgement, peer review, local policy, or treatment-planning assessment.
The UK 2022 SABR constraints were not developed as re-irradiation constraints. Applying recovery percentages and converting between fractionations are modelling assumptions introduced by this calculator.
Spatial overlap, DVH geometry, organ architecture, treatment interval, uncertainty in α/β, dose accumulation method, and other clinical factors must be assessed separately.
Offline use
This calculator can be installed and used without an internet connection after the first online setup.
iPhone / iPad
- While connected to the internet, open this website in Safari.
- Tap the Share button.
- Choose Add to Home Screen, then tap Add.
- Open the calculator once from its new Home Screen icon while you are still online. This allows the app files and constraint library to be cached.
- After that, the calculator can be opened from the Home Screen and used when Wi-Fi and mobile data are unavailable.
Android
- While connected to the internet, open this website in Chrome.
- Open the browser menu and choose Install app or Add to Home screen (wording varies by device).
- Open the installed calculator once while still online so the current app files are cached.
- It can then be launched from its icon and used offline.
Check that offline mode is ready
- Complete the installation steps above.
- Close the calculator.
- Turn on Airplane Mode.
- Open the calculator from its Home Screen/app icon.
- Confirm that the constraint dropdowns and BED/EQD2 calculations work normally before relying on offline access.
What works offline: the calculator, embedded UK 2022 constraint library, BED/EQD2 calculations and internal dual-engine verification.
What still needs internet: external websites and references, including EQD2.com. A manual EQD2.com value can still be entered later for comparison.
Updates: reconnect to the internet and reopen the calculator periodically to receive a newer version. If an old version remains cached, close and reopen the app while online; if necessary, remove the Home Screen installation and install it again.
Important: offline availability depends on the browser/device retaining its cached website data. Verify offline operation on the device before use where connectivity may be unavailable.