Radiobiology Calculator

Treatment Parameters

Gy
Gy
Formulas:
BED = D × [1 + d/(α/β)]
EQD2 = D × [(d + α/β)/(2 + α/β)]
D = total dose, d = dose per fraction

Results

Treatment Summary

Tissue: Standard Tumor
α/β Ratio: 10.0 Gy
Total Dose: 60.0 Gy
Fractionation: 30 × 2.0 Gy

Biological Effectiveness

BED: 72.0 Gy
EQD2: 60.0 Gy

Clinical Interpretation

Standard fractionation (2 Gy/fx) for this tissue type.

Compare Fractionation Schemes

Compare the biological effectiveness of different fractionation schemes for the same tissue type.

Standard Fractionation

30 fractions × 2.0 Gy
60 Gy
BED: 72.0 Gy
EQD2: 60.0 Gy

Hypofractionation

20 fractions × 3.0 Gy
60 Gy
BED: 78.0 Gy
EQD2: 65.0 Gy

SBRT/SRS

5 fractions × 12.0 Gy
60 Gy
BED: 132.0 Gy
EQD2: 110.0 Gy

Key Insights

  • Standard fractionation (2 Gy/fx): Maximizes therapeutic ratio by sparing late-responding normal tissues
  • Hypofractionation: More effective for tumors with low α/β (prostate, breast) while sparing late effects
  • SBRT/SRS: Very high BED from large fractions - best for tumors with low α/β or when late effects are minimal
  • EQD2 comparison: Allows direct comparison of different schemes on a standardized 2 Gy/fx scale

α/β Ratio Reference Values

Reference values for alpha/beta ratios used in radiobiological calculations. Lower α/β indicates greater fractionation sensitivity.

Tumor Tissues

Tumor Type α/β Ratio (Gy) Fractionation Sensitivity Clinical Notes
Melanoma 0.6 - 2 Very High Benefits from hypofractionation
Prostate Cancer 1.5 - 2 Very High Ideal for hypofractionation/SBRT
Breast Cancer 3.5 - 4 High Moderate hypofractionation effective
Sarcomas ~4 High Variable by subtype
Cervix ~10 Low Standard fractionation preferred
Head & Neck SCC 10 Low Conventional fractionation
Lung (NSCLC) 10 Low Standard fractionation or SBRT for early stage
Most Solid Tumors 10 - 12 Low Conventional fractionation standard

Normal Tissues

Tissue α/β Ratio (Gy) Response Type Clinical Importance
CNS/Brain 2 Late Critical - irreversible damage
Spinal Cord 2 Late Critical - myelopathy risk
Kidney 3 Late Nephritis, functional loss
Lung 3 - 4 Late Pneumonitis, fibrosis
Rectum 3 - 5 Late Proctitis, bleeding, stricture
Bladder 3 - 5 Late Cystitis, contracture
Liver 2.5 Late Hepatitis, failure
Heart 3 Late Pericarditis, cardiomyopathy
Skin/Mucosa >10 Early Acute reactions, recoverable
Bone Marrow ~10 Early Hematologic toxicity

Organ Dose Tolerance Limits

Reference tolerance doses for conventional fractionation (1.8-2 Gy/fx). TD5/5 = 5% complication risk at 5 years. TD50/5 = 50% complication risk at 5 years.

Gy

Tolerance Assessment

Organ: Spinal Cord
Delivered Dose: 45.0 Gy
TD5/5: 50 Gy
TD50/5: 70 Gy
Status: SAFE
Dose is below TD5/5 - minimal risk of complications.

Complete Tolerance Reference (Conventional Fractionation)

Organ Volume TD5/5 (Gy) TD50/5 (Gy) Endpoint
Spinal Cord 5-10 cm 50 70 Myelitis, necrosis
Brainstem Whole 50 65 Necrosis, infarct
Optic Nerve/Chiasm Whole 50 65 Blindness
Lens Whole 10 18 Cataract
Retina Whole 45 65 Blindness
Brain Whole 45 60 Necrosis, infarct
Brain 1/3 60 75 Necrosis
Lung Whole 17.5 24.5 Pneumonitis
Lung 1/3 45 65 Pneumonitis
Heart Whole 40 50 Pericarditis
Heart 1/3 60 70 Pericarditis
Kidney Whole 23 28 Nephritis
Kidney 1/3 50 N/A Nephritis
Liver Whole 30 40 Hepatitis, liver failure
Rectum Whole 60 80 Severe proctitis, necrosis, fistula
Bladder Whole 65 80 Contracture, volume loss
Small Intestine Whole 45 55 Obstruction, perforation, fistula
Parotid Gland Whole 32 46 Xerostomia

Important Notes

  • TD5/5: 5% probability of complication within 5 years
  • TD50/5: 50% probability of complication within 5 years
  • These values apply to conventional fractionation (1.8-2 Gy per fraction)
  • For hypofractionation or SBRT, use EQD2 conversion with appropriate α/β ratios
  • Serial organs (spinal cord, optic nerve): Maximum point dose is critical
  • Parallel organs (lung, kidney, liver): Mean dose and volume parameters matter
  • Modern guidelines (QUANTEC, HyTEC) provide dose-volume constraints beyond simple TD values

Understanding Radiobiology

Linear-Quadratic Model

  • Cell killing occurs through two mechanisms: single-hit (α) and double-hit (β)
  • α/β ratio represents the dose where single-hit and double-hit killing are equal
  • Low α/β (1-5 Gy): High fractionation sensitivity - benefits from larger fractions
  • High α/β (>10 Gy): Low fractionation sensitivity - conventional fractionation preferred

Clinical Applications

  • BED: Quantifies biological effect accounting for fractionation
  • EQD2: Converts any schedule to equivalent 2 Gy/fx dose
  • Therapeutic ratio: Exploit differential α/β between tumor and normal tissue
  • Hypofractionation: Most effective when tumor α/β < normal tissue α/β