What should you know about the EQD2 formula in radiotherapy?

Radiotherapy is given in fractions, and the effect depends on both the total dose and the dose per fraction. EQD2 uses a radiobiological model to estimate how one schedule relates to a schedule using conventional fractions. The calculation includes the tissue's alpha-beta value, which represents how sensitive that tissue is to changes in fraction size.

EQD2 is an estimate for comparison, not a separate treatment and not a promise about tumour control or side effects. The result can differ for tumour tissue and nearby healthy organs, so clinicians consider each separately.

Ask the radiotherapy team what the figure refers to: the tumour, a particular organ, or a prior course of treatment. Confirm the total dose, dose per fraction and number of fractions used in the calculation, because changing any of these changes the comparison.

Keep the explanation with your treatment records, especially if you have had radiotherapy before. The team may use EQD2 when planning a new course, assessing overlap with an earlier field, or comparing schedules for conditions such as breast, bowel, brain, cervical or head and neck cancers.

Contact your treatment team promptly for worsening pain, new weakness, confusion, severe headache, repeated vomiting, breathing difficulty, inability to swallow fluids, or a rapidly worsening skin reaction during or after radiotherapy. EQD2 does not replace advice about symptoms.

Which tissue was this EQD2 calculated for? What assumptions were used? How does it affect my plan or the dose to nearby organs? Does previous radiotherapy change the interpretation?