Dynamic simulation of motion effects in IMAT lung SBRT

Area of Science:

• Radiation Oncology
• Medical Physics
• Cancer Treatment

Background:

• Intensity modulated arc therapy (IMAT) is standard for lung cancer Stereotactic Body Radiotherapy (SBRT).
• Dose optimization typically uses static CT, potentially causing discrepancies between planned and delivered radiation due to motion interplay.
• Investigating these dosimetric consequences is crucial for accurate treatment.

Purpose of the Study:

• To evaluate the dosimetric impact of interplay effects in lung cancer SBRT using dynamic CT simulations.
• To compare dose delivery accuracy between static and dynamic simulations for planning and Intensity modulated arc therapy.

Main Methods:

• Retrospective analysis of 15 Stage I NSCLC patients undergoing SBRT (50 Gy/4 fractions).
• Dynamic dose delivery was simulated using 4D-CT data and machine log files.
• Dose accumulation and comparison with static CT-based plans were performed.

Main Results:

• Planning Target Volume (PTV) dose coverage showed <1.5% variation between static and dynamic simulations.
• Average inter-fraction and cumulative dosimetric effects were minimal (<0.5% for PTV coverage, <0.8 Gy for OARs).
• Significant dose variations (up to 7.8 Gy) were observed in organs near the target, such as great vessels and the bronchus.

Conclusions:

• Lung cancer SBRT with IMAT demonstrates limited dose variation for target coverage and OAR constraints under dynamic conditions.
• Critical organs adjacent to the tumor are susceptible to substantial dose variations due to interplay effects.
• Dynamic simulation is essential for accurately assessing dose delivery in SBRT, especially for tumors near critical structures.