Relation between tolerance dose and treatment field size in radiotherapy

Area of Science:

• Radiotherapy
• Radiation Oncology
• Medical Physics

Background:

• Clinical data on skin tolerance doses for various radiotherapy field sizes were analyzed.
• Existing models for radiation dose prescription do not fully account for field size effects.

Purpose of the Study:

• To develop a relationship between radiation tolerance dose and treatment field size.
• To generalize the National System for Dosimetry (NSD) equation by incorporating field-size dependence.

Main Methods:

• Analysis of available clinical data on skin-tolerance doses.
• Log-dose versus log-field-size plotting for different fractionation schedules.
• Combining the derived power law relation with Ellis' NSD equation.

Main Results:

• A power law relationship between tolerance dose and field size was identified.
• Isoeffect lines on log-log plots showed a consistent slope across fractionation schedules.
• A generalized NSD equation incorporating field-size dependence was formulated.

Conclusions:

• The identified power law relation provides a basis for a generalized NSD equation.
• Further data are required to validate the generalized NSD relation under diverse treatment conditions.
• Accurate radiotherapy dose prescription necessitates considering field size alongside dose, time, and fractionation.