Leakage reduction for the Siemens Moduleaf.

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• The Moduleaf add-on miniature multileaf collimator (MMLC) for Siemens Oncor linear accelerators offers high-resolution field shaping.
• Anisotropy in leakage and scatter dose distributions along the x and y axes, and significant inter-leaf leakage, present challenges for accurate modeling in treatment planning systems.

Purpose of the Study:

• To address discrepancies in leakage and scatter dose distributions observed with the Moduleaf MMLC.
• To improve the accuracy of dose modeling for the Moduleaf MMLC within the Pinnacle treatment planning system.

Main Methods:

• Gaps in the Moduleaf frame were filled with lead sheets.
• The Siemens MLC was operated in MLC mode, with leaves closed behind the Y jaws, to create a defined rectangular field.
• Leakage and scatter dose distributions were measured and compared to Pinnacle treatment planning system profiles.

Main Results:

• The modifications significantly reduced the difference between x-axis and y-axis leakage patterns.
• Maximum leakage doses outside the treatment region were reduced to 0.43%.
• The mean square error between calculated and measured dose profiles in the tail region was reduced.

Conclusions:

• Modifications to the Moduleaf MMLC effectively resolved issues with anisotropic leakage and scatter dose distributions.
• The implemented changes enhance the accuracy of dose calculations for radiation therapy planning involving the Moduleaf MMLC.