2. The biologically effective dose (BED) is an approximate quantity by which different fractionation regimens may be intercompared. It is calculated as:
BED = n × d × (1 + (d / (α/β)))
where n = number of fractions, d = dose/fraction, total dose = n × d, and α/β = dose at which the linear and quadratic components of cell kill are equal (for early or late effects).
Assume a conventional treatment regimen of 30 fractions of 200 cGy given one fraction per day, 5 days per week, for an overall treatment time of 6 weeks. The BED for acute (early) effects is 72 Gy_{10} and 100 Gy_{3} for late effects. The subscripts to the Gy are reminders that BED is not in true physical Grays and is applicable only to the particular value of α/β used in the calculation.

3. To compare acute effects for a schedule of 30 fractions with with a proposed schedule of fewer fractions, you must change the number of fractions in the calculator. You can work with any two of the three interrelated parameters (total dose, n, and d) by locking the parameter you wish to hold constant. Unlocked parameters have editable fields. The parameter currently highlighted in red can be bumped up or down in fixed increments using the large buttons with red centers. You can change the context of the red buttons by tapping the label to the left of the parameter you want to control. You can enter exact values by taping in the text field and using the virtual keyboard. BED is automatically updated when any input parameter (total dose, n, d or α/β) is changed.
Lock the total dose field and change the new number of fractions to 25 as illustrated above. The dose/fraction will change automatically to maintain a (locked) total dose of 6000 cGy and the BED readout will automatically calculate 74.4 Gy_{10}.

4. Next, relock the number of fractions and reduce the dose/fraction field until the biologically effective dose returns to approximately 72 Gy_{10}. If the assumption of an α/β ratio ≈ 10 Gy is valid, these two schedules should result in approximately equivalent acute biological effects.
While it is permissible to compare the biologically effective doses calculated for acute effects (in Gy_{n}) of one schedule with acute effects of other schedules (or, likewise, late vs. late effects), it is not permissible or meaningful to compare acute with late effects. Switch between acute or late effects by tapping the "acute" or "late" button next to the α/β field.
