Evaluating which plan quality metrics are appropriate for use in lung SBRT

Area of Science:

• Radiation Oncology
• Medical Physics
• Radiotherapy Planning

Background:

• Evaluating treatment plan quality in lung stereotactic body radiation therapy (SBRT) is crucial for patient outcomes.
• Existing literature proposes various dose metrics for assessing plan quality, categorized into homogeneity, coverage, conformity, and gradient.

Purpose of the Study:

• To apply established dose metrics to characterize lung SBRT dose distributions.
• To identify specific plan quality metrics suitable for routine assessment in lung SBRT.

Main Methods:

• Retrospective review of 90 lung SBRT patient treatment plans (91 targets).
• Dose calculations performed using anisotropic analytical algorithm (AAA) with heterogeneity correction.
• Quantification and analysis of plan quality metric values (coverage, homogeneity, conformity, gradient) using dose-volume histogram data.

Main Results:

• Radiation Therapy Oncology Group (RTOG) defined metrics showed: coverage (0.90 ± 0.08), homogeneity (1.27 ± 0.07), conformity (1.03 ± 0.07), and gradient (4.40 ± 0.80).
• Strong correlations observed between geometric conformity and conformity index (p < 0.0001), and gradient measures and target volume (p < 0.0001).
• RTOG lung SBRT protocol conformity guidelines were met in ≥94% of cases; mean V₂₀ and V₅ were 4.8% (±3.2) and 16.4% (±9.2) respectively.

Conclusions:

• Recommended metrics for lung SBRT plan quality guidelines include coverage % (ICRU 62), conformity (CN or CI_Paddick), and gradient (R_50%).
• Strong recommendation for RTOG lung SBRT protocols to adopt CN or CI_Paddick for conformity evaluation, replacing the prescription isodose to target volume ratio.
• The identified metrics serve as valuable tools for establishing and refining lung SBRT plan quality guidelines.