RADIATION DOSE

Field Size and Dose

Radiation Dose and field size:

Tumor size Margin Doses
< 2 cm 1.0 to 1.5 cm margin 64 Gy in 32 fractions
55 Gy in 20 fractions
50 Gy in 15 fractions
35 Gy in 5 fractions
> 2 cm 1.5 to 2.0 cm margin 66 Gy in 33 fractions
55 Gy 20 fractions

Post surgical RT

  • to 50 Gy in 20 fraction or
  • to 60 Gy in 30 fraction.

Poor Performance status

  • 32 Gy in 4 fractions
  • 20 in 1 fraction for small lesions.

Electron beam vs Orthovoltage

  • wider field margin is needed than with orthovoltage due to wider penumbra
  • dose specified at 90% of the Dmax to account for the relative biologic difference between the two modalities.
  • orthovoltage dose is specified at Dmax (skin) to account for the relative biologic difference between the two modalities.
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