Clinically relevant quality assurance (QA) for prostate RapidArc plans: gamma maps and DVH-based evaluation

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Quality Assurance

Background:

• RapidArc radiotherapy offers precise dose delivery for prostate cancer.
• Independent verification of treatment plans is crucial for patient safety.
• Evaluating quality assurance (QA) methods ensures treatment accuracy.

Purpose of the Study:

• To clinically evaluate quality assurance (QA) tests for RapidArc prostate patients.
• To compare the effectiveness of whole-grid versus per-structure gamma analysis.
• To assess the correlation between gamma passing rates and dose-volume histogram (DVH) discrepancies.

Main Methods:

• Verified 26 RapidArc prostate plans using the COMPASS system for independent dose reconstruction.
• Performed gamma analysis with 3%-3mm and 2%-2mm criteria on whole-grid and per-structure bases.
• Conducted DVH-based analysis for target and organs-at-risk (OAR), correlating with gamma passing rates using Pearson's test.

Main Results:

• No significant DVH deviations were observed for target and OAR.
• A weak negative correlation was found between gamma passing rates and dosimetric deviations.
• The whole-grid gamma method lacked sensitivity for deviations >5%, while per-structure gamma showed better sensitivity and specificity.

Conclusions:

• Per-structure gamma analysis, particularly with 2%-2mm criteria, is recommended for improved sensitivity and specificity in RapidArc prostate QA.
• DVH-based analysis is encouraged when feasible due to poor correlation between standard gamma passing rates and DVH goals.
• Structure-specific gamma methods are strongly suggested for robust radiotherapy quality assurance.