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.

▸How to use this calculator

Re-irradiation cases are among the most difficult to plan and peer review. Image fusions between courses must be inspected directly — they cannot always be trusted — and the dose contributions from both courses must be evaluated together. Above all, these cases require clinical judgment; no calculator replaces it.

To identify the relevant organs at risk, focus on the dose cloud around the new PTV (e.g., a ReRT PTV_Ev10/20 structure, or a 1–2 cm ring around the new PTV). Re-irradiation is often highly conformal, and the high-dose cloud is typically what drives toxicity. For mobile structures such as small bowel, cumulative dose estimates for individual loops may be impossible because loops cannot be reliably registered between courses; point-based estimation may be required.

Re-irradiation is an area of active development. For further information, refer to the numerous publications of the ESTRO Reirradiation Focus Group and the Reirradiation Collaborative Group (ReCOG).

Enter each organ's prior physical D0.1cc dose (Gy) for every prior course. The tool converts to EQD2, subtracts cumulative prior dose from tolerance, and returns the maximum allowable new-plan physical D0.1cc (cGy).

Prior courses & organ doses

Organ at risk
Prior course 1
# fx
time
unit

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)

OrganPrior cum. EQD2
No-Forgive (cGy)		Prior cum. EQD2
Michigan (cGy)		Michigan
new D0.1cc		NF — Safer
new D0.1cc		NF — Borderline
new D0.1cc
—select an organ
Michigan: time-forgiveness on prior EQD2 (2025 discount schedule).NF Safer / Borderline: no forgiveness; two tolerance tiers.NO RESERVEprior dose ≥ tolerance.N/Alimit not defined for this organ/method.

* Kidneys, Liver, 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 no-forgiveness “Safer” and “Borderline” metrics shown in this tool are a sample selected from metrics at www.cancerretreatment.org.

▸Advanced — edit reference tolerances & α/β

Edits apply immediately to the results above. Discount schedule is fixed to the 2025 Michigan values in this version.

Organα/β (NF)α/β (Mich)Michigan lifetime EQD2 (cGy)NF Safer EQD2 (cGy)NF Borderline EQD2 (cGy)Discount schedule (yr : % forgiven)
No organs selected — add organs above, or check “Show All”.
▸Advanced — edit 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%); if checked, customizable time-forgiveness areas are added to Results and Advanced section. N/A means there is no specific time-forgiveness guidance from Michigan for that OAR; you may still enter a custom value.

OrganPrior course 1
Michigan forgiveness
Select organs in “Prior courses & organ doses” above to see their forgiveness values.
The use of time-forgiveness methodology in re-irradiation is controversial. At the University of Michigan, 18% of cases accepted deviations from recommended dose limits. Many additional caveats apply to both time-forgiveness and no-forgiveness methodologies.

Method. EQD2 = D · (d + α/β) / (2 + α/β), with d = D/n, applied only when d > 2 Gy (otherwise physical = EQD2). Michigan multiplies each prior course's EQD2 by (1 − discount), where the discount (fraction forgiven) increases with time since that course. Cumulative prior EQD2 is subtracted from the organ's lifetime/tolerance EQD2; the remainder is back-converted to a physical dose for the new plan's fraction count. If a course's time-since entry is blank, 0% forgiveness is applied (the full prior EQD2 is counted). 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.