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BED Calculator (Biological Effective Dose)DS-GPA Score (Diagnosis-Specific GPA)EQD2 Calculator (Equivalent Dose in 2Gy)GPA Score (Graded Prognostic Assessment)Iso-effective Dose Converter NSD Calculator (Ellis Formula)RPA Grading for Brain Metastases Radiation Necrosis MRI Index SRS Dose Selection (RTOG)TDF Factor (Time-Dose-Fractionation)

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Radiation Oncology

TDF Factor (Time-Dose-Fractionation)

Radiobiology History: TDF Factor

Regimen Details

Dose Per Fraction (cGy)

*Note units in cGy (1 Gy = 100 cGy)

Number of Fractions

Treatment Days Per Week

Historical Context Mode

Calculate the TDF factor to compare current plans with legacy 1970s-1990s radiation oncology protocols.

Guidelines & Evidence

Verified

Last Review: 2026

History & Concept

Origin of TDF

The TDF system was developed by Orton and Ellis in 1973 as a practical clinical tool to simplify the Nominal Standard Dose (NSD) equation. It was designed to allow clinicians to easily add together the biological effects of different treatment phases. While largely superseded by the BED (Linear-Quadratic model) in modern practice, it remains a valuable reference for historical data and some long-term clinical trial analysis.

The TDF Equation

$$TDF = n imes d^{1.538} imes X^{-0.169} imes 10^{-3}$$ Where: n = number of fractions, d = dose per fraction (cGy), X = fractionation interval (days per week factor).

Last Comprehensive Review: 2026