Re-irradiationCalculator
EQD2-based D0.1cc point-dose budgeting for re-irradiation — University of Michigan (time-forgiveness) & No-Forgiveness (Safer / Borderline) methods.
Reference data & logic ported from “Re-irradiation Spreadsheet w EQD2 calc JMR 2.12”. Educational and reference use only. This tool reproduces published EQD2 arithmetic from the cited literature. It does not determine, recommend, or constrain treatment for any individual patient. Verify every value independently.
▸Before you begin — clinical context
The purpose of this calculator is to set the table for dosimetry. Most treatment planning systems cannot optimize against cumulative EQD2, but they optimize readily against absolute dose in the planned fractionation scheme. This tool bridges that gap: it takes each OAR's remaining EQD2 budget and returns it as a maximum physical D0.1cc for the new plan, in the fractionation you intend to deliver.
Re-irradiation cases are among the hardest to plan and peer review. Inspect image fusions between courses directly — they cannot always be trusted — and evaluate dose from both courses together. These cases require clinical judgment; no calculator replaces it.
To identify relevant OARs, focus on the dose cloud around the new PTV (e.g., a ReRT PTV_Ev10/20 structure, or a 1–2 cm ring). Re-irradiation is usually highly conformal, and the high-dose cloud is what drives toxicity. For mobile structures such as small bowel, individual loops cannot be reliably registered between courses, so cumulative dose per loop may be impossible to estimate; point-based estimation may be required.
The two methods use different α/β values, which is why their prior cumulative EQD2 values differ. Michigan uses 2.5 by default; the no-forgiveness method uses 3 for non-CNS/PNS structures and 2 for CNS/PNS. See the S1 supplement of the Michigan publication for default α/β, lifetime EQD2 limits, and time-forgiveness values per OAR. All three — tolerances, α/β, and custom time forgiveness — are editable in the expandable sections at the bottom of this widget.
Read both Michigan papers, and slides 22–31 of this PowerPoint, for further detail — including the finding that 18% of Michigan cases exceeded recommended OAR tolerances. Reasons given: prioritizing target coverage (63%), deviation within the margin of uncertainty (10%), use of de novo SBRT limits (10%), high uncertainty in composite dose (6%), and prior course alone exceeding the cumulative limit (3%).
Re-irradiation is an area of active development. See the publications of the ESTRO Reirradiation Focus Group and the Reirradiation Collaborative Group (ReCOG) for more, along with the ESTRO reirradiation webinars: Challenges in Reirradiation: From Art to Science and the 2nd ESTRO ReRT webinar. This tool is not endorsed by any reirradiation group or professional society.
Other resources worth knowing: cancerretreatment.org and Rad Onc Review's reRT sections (general re-irradiation guidance in the palliation section, plus re-irradiation guidance within each relevant disease-site document), Rad Onc Calc's detailed reRT reference list for each OAR (including the linked source papers), and the two Michigan papers, ReCOG, ESTRO/EORTC, and E2-RADIatE/ReCare studies. The real answer: phone a friend, learn your institution's workflow, and build one if it doesn't exist. There is no single “best resource”; this is one of the most challenging things we do.
Prior courses & organ doses
| Organ at risk | Prior course 1 # fx Time since this course | |
|---|---|---|
Each course column shares its # fractions and time-since across all organs (as in the spreadsheet). Leave a dose blank if that organ was not exposed in that course.
Results — max new-plan physical D0.1cc (Gy)
New Plan D0.1cc values depend on the desired cumulative tolerances, with or without time forgiveness. See the Reference tolerances & α/β section below for more information.
Without Time Forgiveness
| Organ | Prior cum. EQD2 (Gy) | “Safer” New Plan D0.1cc | “Borderline” New Plan D0.1cc |
|---|---|---|---|
| — | select an organ | ||
The no-forgiveness “Safer” and “Borderline” metrics shown in this tool are a sample selected from metrics at www.cancerretreatment.org.
With Time Forgiveness (Michigan default)
* Kidneys, liver, and lungs are mean-dose organs — no point-dose lifetime limit is defined (shown N/A). “OTHER” has no Michigan time-forgiveness schedule, so Michigan results cannot be computed. The two Prior cum. EQD2 columns differ because the methods use different α/β (see above). Tolerances, α/β, and custom time forgiveness are editable below.
▸Reference tolerances & α/β
Edits apply immediately to the results above. Discount schedule is fixed to the 2025 Michigan values in this version.
| Organ | α/β (NF) | α/β (Mich) | Michigan lifetime EQD2 (Gy) | NF Safer EQD2 (Gy) | NF Borderline EQD2 (Gy) |
|---|---|---|---|---|---|
| No organs selected — add organs above, or check “Show All”. | |||||
▸Advanced — time-forgiveness (default Michigan)
Michigan forgiveness (% of prior EQD2 forgiven) is derived from each course's time-since entry above; a blank time is treated as 0% forgiveness. Check Custom time forgiveness to override any value (0–100%) — this adds custom columns to the Results and Advanced sections. N/A means there is no time-forgiveness guidance from Michigan for that OAR; you may still enter a custom value.
| Organ | Prior course 1 Michigan forgiveness | Michigan Time forgiveness schedule (yr : % forgiven) |
|---|---|---|
| Select organs in “Prior courses & organ doses” above, or check “Show All”. | ||
EQD2 = D · (d + α/β) / (2 + α/β), with d = D/n, where D = total physical dose (Gy), n = number of fractions, d = dose per fraction (Gy), and α/β = the tissue-specific alpha/beta ratio (Gy) for the organ and method selected.
Full EQD2 (default) applies this formula at all fraction sizes. Intermediate EQD2 applies it only when d > 0.5 Gy; for d ≤ 0.5 Gy, physical dose is used as EQD2. Conservative EQD2 applies it only when d > 2 Gy; for d ≤ 2 Gy, physical dose is used as EQD2.
Back-conversion of the remaining EQD2 budget to new-plan physical dose uses the same threshold test as forward conversion: return the budget as-is when the new-plan fraction size is at or below the selected mode's threshold, otherwise solve the full formula.
Method. Michigan multiplies each prior course's EQD2 by (1 − discount), where the discount grows with time since that course; a blank time-since applies 0% forgiveness, so the full prior EQD2 is counted. Cumulative prior EQD2 is subtracted from the organ's lifetime tolerance EQD2, and the remainder is back-converted to a physical dose for the new plan's fraction count. Custom time-forgiveness values, when enabled, replace the Michigan schedule for that organ and course.
Intended purpose. This calculator is an educational and reference tool for reproducing the EQD2 and cumulative-dose arithmetic described in the cited publications. Its output is a numerical illustration of those published methods. It is not intended to diagnose, prevent, monitor, predict, prognose, or treat any disease, and it is not intended to determine or constrain the treatment of any individual patient. All clinical decisions remain the sole responsibility of the treating physician, who must independently verify every input, assumption, and result against institutional protocols and primary sources.
Regulatory status. This tool is not a medical device. It is not CE marked and has not undergone conformity assessment under Regulation (EU) 2017/745, and it is not UKCA marked or registered under the UK Medical Devices Regulations 2002 (as amended). It is not placed on, or made available on, the market of the European Union, EEA, Switzerland, or the United Kingdom, and it is not intended for use by persons in those territories. It has not been reviewed or cleared by the US Food and Drug Administration.
Privacy. All calculations run entirely in your browser. No values you enter are transmitted, stored, logged, or retained by this site or any third party. Nothing you enter leaves your device, and closing or reloading the page discards it. Do not enter patient names, identifiers, or any protected health information; none is required.
No warranty. This tool is provided “as is” and “as available,” without warranty of any kind, express or implied, including any warranty of accuracy, completeness, currency, merchantability, or fitness for a particular purpose. The underlying tolerance values, α/β assumptions, and time-forgiveness schedules are drawn from the cited literature and may be incomplete, superseded, or inapplicable to a given case.
Limitation of liability. To the maximum extent permitted by law, the author and contributors accept no liability for any direct, indirect, incidental, consequential, or special loss or damage arising from use of, or reliance on, this tool.
Governing law. These terms are governed by the laws of the State of West Virginia, USA, without regard to conflict-of-law rules. Any dispute is subject to the exclusive jurisdiction of the courts located there.
Version and provenance. Calculator version 3.0, released 8/18/2026. Reference dataset derived from “Re-irradiation Spreadsheet w EQD2 calc JMR 2.12,” last reviewed 8/18/2026. Michigan time-forgiveness schedule: 2025 values.
Contact. Rad Onc Review. feedback@radoncreview.org. Report a suspected error to the same address.
Credits. Jeff Ryckman, MD, MSMP. Special thanks to Alf Siochi, PhD, DABR, and Matt Culbert, MD.