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”. For clinical decision support only — verify 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.
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 (cGy)
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 (cGy) | “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 α/β, so EQD2/Michigan 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 (cGy) | NF Safer EQD2 (cGy) | NF Borderline EQD2 (cGy) |
|---|---|---|---|---|---|
| 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”. | ||
Method. EQD2 = D · (d + α/β) / (2 + α/β), with d = D/n, applied only when d > 2 Gy (otherwise physical dose = EQD2). Michigan multiplies each prior course's EQD2 by (1 − discount), where the discount grows with time since that course; a blank time-since counts the full prior EQD2. 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.
Disclaimer. This calculator is a decision-support aid, not a substitute for clinical judgment or independent verification. Confirm all values, α/β assumptions, and institutional tolerances before use in patient care.
Credits. Jeff Ryckman, MD, MSMP. Special thanks to Alf Siochi, PhD, DABR, and Matt Culbert, MD.