The linear quadratic (LQ) model in radiobiology uses the alpha/beta ratio to describe tissue radiosensitivity. A tissue with a LOW alpha/beta ratio (e.g., 2-3 Gy) is characterized by:
- A High sensitivity to large doses per fraction (hypofractionation) ✓
- B High sensitivity to small doses per fraction (hyperfractionation)
- C Rapid proliferating cells with fast repair
- D High tolerance to single-fraction stereotactic body radiation therapy
Explanation
Low alpha/beta ratio tissues (2-3 Gy; e.g., prostate cancer, breast cancer, late-responding normal tissues like spinal cord) have a large shoulder on the cell survival curve, indicating better sublethal damage repair at small doses but disproportionately greater cell killing with large doses per fraction. These tissues benefit from hypofractionation (larger doses per fraction, fewer fractions) — the basis for prostate SBRT (5 fractions) and breast hypofractionation schedules. High alpha/beta tissues (e.g., bowel, head-neck tumors ~10 Gy) are sensitive to small dose per fraction and benefit from conventional fractionation or hyperfractionation.
Reference: Grainger & Allison's Diagnostic Radiology, 7th ed.
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Written and medically reviewed by the StethoPrep medical team.