Calculating geometrical margins for hypofractionated radiotherapy

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Traditional radiotherapy margin calculations assume a large number of small fractions.
• Hypofractionated radiotherapy (≤5 fractions) is increasingly common, challenging existing margin formulae.
• Existing methods may lack accuracy for regimens with limited fractions.

Purpose of the Study:

• To develop and validate an algorithm for accurate margin calculation in hypofractionated radiotherapy.
• To provide reliable margin estimates for treatment regimens with as few as two fractions.

Main Methods:

• Developed a novel algorithm for calculating radiotherapy margins.
• Incorporated a method for estimating the upper margin limit.
• Adjusted the van Herk formula to provide a lower margin limit.
• Used a single-term mathematical model for interpolation between limits.
• Validated results against Monte Carlo simulations.

Main Results:

• The proposed algorithm accurately estimates required margins within approximately 1%.
• Accuracy is maintained across a wide range of systematic errors, random errors, and penumbral widths.
• The method is effective even for hypofractionated regimens with as few as two fractions.

Conclusions:

• The developed algorithm provides accurate and reliable margin calculations for hypofractionated radiotherapy.
• This approach addresses the limitations of traditional formulae in modern radiotherapy practices.
• The findings support the safe and effective implementation of hypofractionation.