A novel conformity index for intensity modulated radiation therapy plan evaluation

Area of Science:

• Medical Physics
• Radiation Oncology
• Cancer Treatment Planning

Background:

• Intensity modulated radiation therapy (IMRT) is a widely used cancer treatment modality.
• Manual evaluation of IMRT plans for head-and-neck cancers is complex and subjective.
• Objective assessment tools are needed to improve IMRT plan quality and consistency.

Purpose of the Study:

• To develop a personalized conformity index (CI(DD)) for evaluating IMRT plans in head-and-neck cancers.
• To assess the plan quality discerning power of the developed CI(DD) compared to existing indices.
• To provide an objective and geometry-based tool for IMRT plan comparison.

Main Methods:

• A 2D CI incorporating dose and distance (CI(DD)) was developed using MATLAB.
• DICOM RT objects were utilized to compute CI(DD) components, including a distance-based exponential function for cold spot penalty.
• Three nasopharyngeal carcinoma (NPC) patient datasets were used to generate 10 IMRT plans of varying quality for evaluation.

Main Results:

• The CI(DD) scoring system successfully incorporated spatial importance of voxels within the planning target volume (PTV).
• CI(DD) accurately ranked IMRT plan quality by considering the relative importance of cold spots, accounting for tumor geometry.
• CI(DD) demonstrated superior discerning power, evidenced by the largest coefficient of variance compared to other CIs.

Conclusions:

• The developed CI(DD) provides a patient-specific, geometry-based index for comparing IMRT plans in head-and-neck cancers.
• CI(DD) enhances plan quality assessment by considering individual tumor geometry, leading to superior discerning power.
• CI(DD) can serve as an effective tool for benchmarking, reducing plan variability, and advancing IMRT planning quality.