Accuracy of dose calculation methods for retracted tissue compensators

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Dose calculations in radiation therapy are complex, particularly with tissue compensators.
• Commercial treatment planning systems often lack precise methods for incorporating compensator effects on scatter dose.

Purpose of the Study:

• To evaluate the accuracy of dose calculations for a wax tissue compensation system.
• To compare experimental measurements with analytical calculations for varying compensator shapes.

Main Methods:

• Measured retraction factors along central-axis and off-axis raylines for various wax compensator shapes.
• Compared measured factors with those derived from effective attenuation coefficient and 3D analytical calculations.

Main Results:

• Simple calculation methods show shape-dependent accuracy, with errors exceeding +/-5% for large variations in missing-tissue thickness.
• The 3D analytical method demonstrated good agreement with experimental measurements.

Conclusions:

• Simple dose calculation methods for tissue compensators can be inaccurate.
• The 3D analytical approach offers a more reliable method for dose calculation with compensators, adaptable for scatter algorithms.