A method using 4D dose accumulation to quantify the interplay effect in lung stereotactic body radiation therapy

Area of Science:

• Medical Physics
• Radiation Oncology
• Radiotherapy Physics

Background:

• Lung stereotactic body radiation therapy (SBRT) requires precise dose delivery.
• Respiratory motion introduces interplay effects between multileaf collimator (MLC) movement and tumor motion, impacting dose accuracy.
• Quantifying dosimetric uncertainty from these interplay effects is crucial for treatment quality.

Purpose of the Study:

• To develop and validate a method for quantifying dosimetric uncertainty caused by MLC-respiratory motion interplay in lung SBRT.
• To assess the impact of irregular breathing patterns, breathing rate, and field size on dose distributions.

Main Methods:

• A novel method was devised to calculate dose distributions across all respiratory phases for dynamic treatments.
• It incorporates patient-specific irregular breathing patterns, selecting critical phases for dose summation.
• Deformable image registration (DIR) was used for dose accumulation, enabling separation of DIR and interplay uncertainties using an Evaluation Target Volume (ETV).

Main Results:

• Tumor coverage uncertainties (D95 and V100) for Gross Tumor Volume (GTV) and ETV were generally small (<2%) in retrospective patient data.
• Significant over- and under-dosages were observed near the ETV, particularly with highly irregular breathing.
• GTV mean dose uncertainties decreased with larger field sizes and increased breathing rates.

Conclusions:

• The developed method effectively quantifies dosimetric uncertainty from interplay effects in lung SBRT, especially for patients with irregular breathing.
• While tumor coverage may be maintained, localized dose deviations near the ETV require attention.
• The method provides a valuable tool for assessing treatment quality and investigating interplay effects in various clinical scenarios.