Tuning a secondary dose verification software for a CT-guided online adaptive delivery system

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Quality assurance (QA) for CT-guided online adaptive radiotherapy (CTgART) platforms is currently unstandardized.
• Secondary dose calculation software, such as Mobius3D, is used for these closed CTgART systems.
• The impact of optimizing dosimetric leaf gap (DLG) correction values for specific delivery techniques in CTgART secondary dose calculations is not well understood.

Purpose of the Study:

• To investigate and optimize the dosimetric leaf gap (DLG) correction value for independent secondary dose verification software.
• To adapt these DLG values for different delivery techniques used in adaptive online QA for CTgART.

Main Methods:

• Evaluated 31 volumetric arc therapy (VMAT) and 13 fixed-gantry intensity modulated radiation therapy (IMRT) plans using patient CT and QA datasets.
• Compared primary treatment planning system (TPS) doses with secondary calculation doses across a range of DLG correction values (-2 to 2 mm) using 3D gamma passing criteria.
• Determined optimal DLG correction values by comparing ion chamber measurements with secondary calculations for both IMRT and VMAT plans.

Main Results:

• Optimal DLG correction values were found to be -0.3 mm for VMAT and 0.4 mm for IMRT.
• Mean gamma passing rates between primary and secondary doses were high: 99.0% ± 1.0% for VMAT and 99.9% ± 0.1% for IMRT (3%/2 mm criteria).
• Mean ion chamber agreement showed good agreement: 0.0% ± 2.1% for VMAT and 0.2% ± 1.4% for IMRT.

Conclusions:

• Dosimetric leaf gap (DLG) correction values should be individually tuned for each delivery technique (VMAT and IMRT).
• This separate tuning is essential for maximizing the robustness and accuracy of CTgART online QA programs.