BED Calculator
Compute Biologically Effective Dose and Equivalent Dose in 2-Gy Fractions using the Linear-Quadratic model
The radiation dose delivered in each treatment session. Standard fractionation uses 1.8–2.0 Gy; hypofractionation uses 2.5–20 Gy per fraction.
The cumulative prescribed dose across all fractions. Equals dose per fraction multiplied by number of fractions.
The tissue-specific radiosensitivity ratio in Gy. Higher values indicate less sensitivity to fractionation changes. Select a preset or enter a custom value.
Acute delivery assumes instantaneous fraction delivery (standard external beam). Protracted delivery applies a dose rate correction factor for slow or continuous delivery such as brachytherapy.
Enter Parameters to Calculate BED
Input the dose per fraction, total dose, and alpha/beta ratio above. Results including BED, EQD2, charts, and clinical interpretation will appear here automatically.
How to Use the BED Calculator
Select Dose Unit and Enter Fraction Parameters
Choose your preferred dose unit — Gy (Gray) or cGy (centigray). Then enter the dose per fraction and total prescribed dose. The calculator automatically derives the number of fractions. For standard fractionation, typical values are 2.0 Gy per fraction with a total dose of 50 to 70 Gy. For SBRT, values might be 10 to 20 Gy per fraction with a total dose of 30 to 60 Gy.
Select the Alpha/Beta Ratio for Your Target Tissue
Choose a predefined tissue preset or enter a custom alpha/beta ratio. Use 10 Gy for most tumors and early-responding tissues, 3 Gy for late-responding normal tissues, 2 Gy for CNS and kidneys, or 1.5 Gy for prostate cancer. The alpha/beta reference table in the results panel provides published ranges for nine common tissue types to help you select the appropriate value.
Configure Delivery Mode and Optional Features
Select Acute for standard external beam delivery or Protracted for continuous low-dose-rate treatments like brachytherapy, then adjust the dose rate factor (g). Optionally, enable the Boost module to add a second treatment course and calculate cumulative BED, or enable Multi-Schema Comparison to evaluate up to five fractionation schedules side by side.
Review Results, Charts, and Export
The results panel displays BED, EQD2, fraction count, and alpha/beta ratio instantly. Review the BED component breakdown donut chart, the multi-ratio bar chart comparing BED across four standard alpha/beta values, and the clinical interpretation notes. Use the Export CSV button to download results for documentation or the Print button to generate a print-friendly version.
Frequently Asked Questions
What is BED and why is it used in radiation therapy?
Biologically Effective Dose (BED) is a radiobiological quantity that expresses the true biological impact of a radiation treatment schedule, accounting for both the total dose and the fractionation pattern. It is derived from the Linear-Quadratic model of cell killing. BED is essential because two treatment regimens delivering the same total physical dose can have very different biological effects depending on the dose per fraction. For example, 60 Gy in 30 fractions of 2 Gy has a different biological effect than 60 Gy in 20 fractions of 3 Gy. BED allows radiation oncologists to quantitatively compare these regimens and ensure that both tumor control probability and normal tissue complication probability are within acceptable limits.
What is EQD2 and how does it relate to BED?
EQD2, or Equivalent Dose in 2-Gy Fractions, converts any fractionation scheme into the total dose that would produce the same biological effect if delivered in standard 2 Gy fractions. It is calculated as EQD2 = D times (d + alpha/beta) divided by (2 + alpha/beta), or equivalently EQD2 = BED divided by (1 + 2/alpha/beta). EQD2 is widely preferred in clinical practice because most radiation oncologists have extensive experience with 2 Gy per fraction regimens and can intuitively interpret dose values in that context. When comparing a hypofractionated SBRT plan to a conventional plan, EQD2 provides a common reference frame.
How do I choose the correct alpha/beta ratio for my calculation?
The alpha/beta ratio depends on the tissue you are evaluating. For most tumors and early-responding normal tissues, use 10 Gy. For late-responding normal tissues such as connective tissue and muscle, use 3 Gy. For the central nervous system including brain and spinal cord, use 2 Gy. For kidneys, published values range from 1.0 to 2.4 Gy. Prostate cancer is a notable exception among tumors with an alpha/beta of approximately 1.1 to 1.5 Gy. Head and neck tumors have higher ratios of 13.8 to 23 Gy. When in doubt, use the reference table provided in this calculator and consult the radiation oncology literature for your specific clinical scenario.
What is the dose rate factor (g) and when should I use protracted delivery mode?
The dose rate factor g is a correction value between 0 and 1 that accounts for the repair of sublethal radiation damage during slow or continuous radiation delivery. In acute delivery mode (standard external beam), each fraction is delivered in minutes and g is effectively 1, meaning no significant repair occurs during irradiation. In protracted delivery, such as continuous low-dose-rate brachytherapy, repair occurs during delivery, reducing the quadratic component of cell killing. A g value of 0.5 means that half of the sublethal damage is repaired during delivery. Select protracted mode for brachytherapy or any scenario where the irradiation time per fraction is significantly longer than the sublethal damage repair half-time of the tissue.
How does the boost dose module work for cumulative BED?
The boost module allows you to add a second radiation treatment course, such as a brachytherapy boost following external beam therapy, or a sequential cone-down boost field. You enter the dose per fraction and total dose for the boost course, and the calculator computes its BED and EQD2 independently. The combined BED is the simple sum of the primary course BED and the boost course BED, which is a valid approach under the LQ model when both courses use the same alpha/beta ratio. This cumulative calculation is essential for ensuring that the total biological dose to critical structures such as the spinal cord, rectum, or bladder does not exceed established tolerance limits.
What are the limitations of the BED calculation?
The BED formula is based on the Linear-Quadratic model, which has several recognized limitations. First, it does not account for tumor cell repopulation during treatment, which can reduce effective tumor BED for protracted courses lasting more than four to five weeks. Second, its accuracy may be reduced at very high doses per fraction above approximately 6 to 8 Gy, though this is debated. Third, treatment breaks and gaps are not modeled, with an estimated correction of about 1 Gy per day of interruption needed. Fourth, the model assumes complete sublethal damage repair between fractions. Fifth, patient-specific biological variability in alpha/beta ratios is not captured by population-average values. Despite these limitations, BED remains the standard clinical tool for fractionation comparison.