A study of effective attenuation coefficient for calculating tissue compensator thickness.

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Dose uniformity is critical for effective radiation therapy.
• Tissue compensators correct for surface irregularities to improve dose uniformity.
• Accurate calculation of compensator thickness is essential for precision treatment.

Purpose of the Study:

• To evaluate the accuracy of using an effective attenuation coefficient for calculating missing tissue compensator thickness.
• To identify conditions where this method introduces significant errors in radiation therapy planning.

Main Methods:

• Investigated the variation of the effective attenuation coefficient with missing tissue thickness.
• Analyzed the impact of initial depth, specifically in the buildup region, on the coefficient.
• Utilized 10-MV x-rays for calculations and error assessment.

Main Results:

• The effective attenuation coefficient varies significantly with missing tissue thickness in the buildup region.
• Employing a single attenuation coefficient resulted in up to 54% error in compensator thickness calculations for 10-MV x-rays.
• Beyond the depth of maximum dose, the coefficient depends on field size, not initial depth.

Conclusions:

• A single effective attenuation coefficient is inaccurate for calculating tissue compensator thickness, particularly in the buildup region.
• The findings highlight the need for more sophisticated methods to ensure accurate dose delivery in radiation therapy.
• Accurate compensator design is crucial for minimizing dose errors caused by surface contour variations.