Development of a spatially indexed dose-volume histogram for treatment plan evaluation

Area of Science:

• Radiation Oncology
• Medical Physics

Background:

• Conventional dose-volume histograms (DVHs) lack spatial information crucial for assessing carotid artery sparing in laryngeal VMAT.
• Evaluating the proximity of critical structures like carotid arteries to the planning target volume (PTV) is vital for optimizing radiotherapy plans.

Purpose of the Study:

• To develop and evaluate a spatially indexed DVH that incorporates distance information for improved laryngeal VMAT plan quality assessment.
• To visually represent the spatial relationship between dose distribution and carotid artery proximity to the PTV.

Main Methods:

• A novel spatially indexed DVH was developed, calculating dose and minimum Euclidean distance to the PTV for each carotid artery voxel.
• Color-coded cumulative DVHs were generated using mean dose-specific distance (MDD) mapped to a color gradient.
• Spatial metrics including minimum distance (dmin,35Gy), mean dose-specific distance (MD35Gy), and V35Gy,10mm were derived at 35 Gy.

Main Results:

• The spatially indexed DVH effectively identified spatial risk transitions in three representative cases (distant, intermediate, proximal).
• The intermediate case showed high-risk areas despite low conventional V35Gy, highlighting the utility of proximity metrics.
• The proximal case demonstrated significant high-dose volume within 10 mm of the PTV surface (V35Gy,10mm), indicating substantial risk.

Conclusions:

• The spatially indexed DVH offers an intuitive method for evaluating the spatial relationship between high-dose regions and the PTV in laryngeal VMAT.
• This approach facilitates enhanced risk stratification and plan optimization for improved carotid artery sparing.