Radiation Therapy Dose Calculator
Calculate dose per fraction, BED (biologically effective dose), EQD2, treatment duration, and weekly dose for radiation therapy planning.
About this calculator
This calculator applies the linear-quadratic (LQ) radiobiology model -- the standard framework radiation oncologists and medical physicists use to compare different fractionation schedules -- to three core outputs: dose per fraction, biologically effective dose (BED), and equivalent dose in 2 Gy fractions (EQD2). Dose per Fraction is simply Total Prescribed Dose divided by Number of Fractions. BED follows the standard LQ formula BED = D x (1 + d/(alpha/beta)), where D is total dose, d is dose per fraction, and alpha/beta is a tissue-specific radiosensitivity ratio: tissues with a low alpha/beta (often cited near 1.5 Gy for prostate) are more sensitive to fraction size and tend to respond well to fewer, larger fractions, while tissues with a high alpha/beta (often modeled near 10 Gy for head/neck and lung tumors, the generic value used for most rapidly dividing tumors when a tissue-specific figure isn't available) respond more similarly across different fractionation schedules. EQD2 converts BED back into the total dose, delivered in the conventional 2 Gy-per-fraction schedule, that would produce the same biological effect -- the common unit used to compare regimens on one scale.
Total Prescribed Dose is the dominant input here: raising it increases dose per fraction, BED, and EQD2 together, holding fractions fixed. This tool is an educational estimator only, not a substitute for actual treatment planning: it applies one representative alpha/beta value per Tumor Type category rather than a patient- and protocol-specific figure, and it does not account for three-dimensional dose distribution, organ-at-risk dose-volume constraints, tissue heterogeneity, treatment gaps, or overall-treatment-time repopulation effects that a radiation oncologist and medical physicist weigh in an actual prescription. The Normal Tissue Constraint field is captured for reference only and does not feed into any calculation on this page.
Medical Disclaimer
This calculator is for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making decisions about your health. Never disregard professional medical advice or delay seeking it because of results from this tool.
This tool estimates a starting point only and is not a validated clinical decision-support system. It does not account for every patient-specific factor (organ function, drug interactions, allergies, comorbidities, or current clinical status). Any dose, rate, or setting must be independently verified by the treating clinician and pharmacist or respiratory therapist against current institutional protocols, product labeling, and the patient's full clinical picture before being administered or applied.
Inputs
Results
Dose per Fraction
2 Gy
How to Use This Calculator
- Enter the total prescribed radiation dose in Gray (Gy).
- Input the number of fractions in the treatment plan.
- Set the treatment days per week.
- Select the tumor type or tissue sensitivity.
- Review the dose per fraction, BED (Biologically Effective Dose), and EQD2 for radiobiology assessment.
How the result changes with Total Prescribed Dose (Gy)
| Total Prescribed Dose (Gy) | Dose per Fraction |
|---|---|
| 30 | 1 Gy |
| 45 | 1.5 Gy |
| 90 | 3 Gy |
| 100 | 3.33 Gy |
What each input means
- Total Prescribed Dose (Gy)
- Total radiation dose prescribed for the full course of treatment.
- Number of Fractions
- Total number of treatment sessions. Standard: 25-35 fractions.
- Treatment Days per Week
- Number of treatment days per week. Standard: 5 (Monday-Friday).
- Tumor Type
- Tissue type determines the representative alpha/beta ratio used in the BED and EQD2 calculations.
- Normal Tissue Constraint (Gy)
- Maximum acceptable dose to adjacent normal tissue.
What each result means
- BED (Biologically Effective Dose)
- Accounts for fractionation effects on tumor cell kill.
How this is calculated
Worked example, using the default values
- Identify Input Parameters4 parametersTotal Prescribed Dose (Gy) = 60, Number of Fractions = 30, Treatment Days per Week = 5, Tumor Type = 3 = 5 input(s) provided
- Calculate Dose per FractionDose per Fraction2 = 2
- Calculate BEDBED72 = 72
- Calculate EQD2EQD260 = 60
Engine last updated . Checked against 3 independently-derived tests — how we verify calculators. Built by Paul Gunder, a software engineer, not a licensed financial, medical, or legal professional.
Frequently Asked Questions
What does BED (Biologically Effective Dose) actually measure?
BED converts a fractionation schedule -- Total Prescribed Dose split across a Number of Fractions -- into a single number representing biological cell-kill effect, using the standard linear-quadratic formula BED = D x (1 + d/(alpha/beta)). It lets clinicians compare regimens with very different dose-per-fraction sizes on one biological scale, which raw total dose in Gy alone cannot do: the same total dose delivered in fewer, larger fractions is biologically more potent than that total split across many small fractions.
Why does the same alpha/beta ratio apply for every case within a given Tumor Type?
This calculator assigns one representative alpha/beta value per Tumor Type category (for example, 1.5 for prostate, 10 for head/neck) because that is the level of detail a simple estimator can support. Published alpha/beta values vary across studies and individual patients, and an actual treatment plan uses tissue- and protocol-specific figures rather than a single lookup number, so treat the Tumor Type selector as illustrative rather than as a confirmed radiobiological parameter for any specific patient.
Does raising the Number of Fractions always lower BED?
Yes, holding Total Prescribed Dose fixed: raising Number of Fractions spreads the same total dose across more, smaller doses per fraction, and because BED grows with dose-per-fraction size (not total dose alone), a smaller dose per fraction produces a lower BED for the same total dose. This is the radiobiological reason schedules with many small fractions are generally gentler per unit of total dose than fewer, larger fractions.
What is EQD2 used for, and how does it differ from BED?
EQD2 re-expresses a schedule's BED as the total dose that would need to be delivered in conventional 2 Gy fractions to produce the same biological effect, using EQD2 = BED / (1 + 2/(alpha/beta)). Where BED is a somewhat abstract effect number, EQD2 is expressed in Gy and can be compared directly against dose totals from historical or standard-fractionation regimens, which is why EQD2 rather than raw BED is the figure most often quoted in radiation oncology literature.
Should this calculator's numbers be used to plan or evaluate an actual radiation therapy course?
No. This tool estimates BED and EQD2 from the same linear-quadratic equations used in radiation oncology, but an actual prescription accounts for three-dimensional dose distribution, organ-at-risk dose constraints, tissue heterogeneity, patient-specific radiosensitivity, and treatment-time effects that a simple four-input calculator cannot capture. Treatment planning and dose interpretation should always be performed by a qualified radiation oncologist and medical physicist using validated treatment-planning software.
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