Accuracy of one algorithm used to modify a planned DVH with data from actual dose delivery

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• Accurate detection and quantification of treatment delivery errors are critical in radiation therapy to ensure patient safety and treatment efficacy.
• Dosimetric verification methods are essential for quality assurance (QA) in radiotherapy.

Purpose of the Study:

• To evaluate the accuracy of dose volume histogram (DVH) based quality assurance (QA) in quantifying radiation therapy delivery errors.
• To compare the sensitivity of 2D and 3D distance-to-agreement (DTA) analyses and DVH-based QA in detecting induced delivery errors.

Main Methods:

• Eighteen VMAT plans (prostate, head and neck, brain) were modified with induced errors: monitor unit differences (±3.0%), control point deletions (3, 5, 8), and gantry angle shifts (±2°).
• Delivery QA was performed using an ArcCHECK detector.
• 2D and 3D DTA analyses were conducted using SNC Patient and 3DVH software, respectively.
• DVH accuracy was assessed by comparing 3DVH predictions against Eclipse treatment planning system recalculations.

Main Results:

• 3D DTA analysis showed high pass rates for error-induced plans, while 2D DTA analysis demonstrated greater sensitivity in detecting delivery errors.
• The average differences in DVH parameters between Eclipse recalculations and 3DVH predictions were within 2% for all error types.
• 3DVH software accurately quantifies delivery errors in terms of the actual dose delivered.

Conclusions:

• 2D DTA analysis is recommended for routine clinical evaluation of radiation therapy delivery accuracy.
• DVH-based QA provides accurate quantification of delivery errors and should be used for further analysis of any dose discrepancies.
• Combining conventional QA with DVH-based analysis ensures clinically relevant results and confirms treatment accuracy.