A quality assurance method that utilizes 3D dosimetry and facilitates clinical interpretation

Area of Science:

• Medical Physics
• Radiation Oncology

Background:

• Intensity-modulated radiotherapy (IMRT) for base-of-skull (BOS) tumors requires precise dosimetry verification.
• Conventional 2D quality assurance (QA) methods may not fully capture the complexity of 3D dose distributions.

Purpose of the Study:

• To introduce and validate a novel 3D dosimetry QA method for BOS IMRT.
• To evaluate the clinical significance of dosimetric deviations using patient-specific data.
• To investigate the dosimetric efficacy of BOS IMRT treatments.

Main Methods:

• Developed a 3D dosimetry QA method using the DLOS/Presage system in an anthropomorphic phantom.
• Acquired isotropic 2-mm resolution dose data within the treated volume.
• Transformed 3D dose data back to the patient's CT for dose-volume histogram (DVH) and dose overlay analysis.
• Compared 3D measured doses with planned doses for 6 BOS IMRT patients.

Main Results:

• The 3D dosimetry method demonstrated close agreement between measured and calculated dose distributions.
• Mean passing rates for gamma criteria (3%, 2 mm) were 96.8% for 2D portal dosimetry and 94.9% for 3D dosimetry.
• Analysis on patient anatomy revealed minor deviations, with their clinical significance discussed.

Conclusions:

• The 3D dosimetry QA method provides comprehensive verification across the entire treated volume.
• The method enables assessment of the clinical relevance of dosimetric deviations through DVH and dose overlays on patient anatomy.
• This approach enhances the clinical significance and relevance of complex IMRT quality assurance.