A margin-based analysis of the dosimetric impact of motion on step-and-shoot IMRT lung plans

作者：Waghorn Benjamin J; Shah Amish P^*; Rineer Justin M; Langen Katja M; Meeks Sanford L

来源：Radiation Oncology, 2014, 9(1): 46.

DOI：10.1186/1748-717X-9-46

• IMRT
• Motion
• Step-and-shoot
• Lung
• Dosimetry

Purpose: Intrafraction motion during step-and-shoot (SNS) IMRT is known to affect the target dosimetry by a combination of dose blurring and interplay effects. These effects are typically managed by adding a margin around the target. A quantitative analysis was performed, assessing the relationship between target motion, margin size, and target dosimetry with the goal of introducing new margin recipes.
Methods: A computational algorithm was used to calculate 1,174 motion-encoded dose distributions and DVHs within the patient's CT dataset. Sinusoidal motion tracks were used simulating intrafraction motion for nine lung tumor patients, each with multiple margin sizes.
Results: D-95% decreased by less than 3% when the maximum target displacement beyond the margin experienced motion less than 5 mm in the superior-inferior direction and 15 mm in the anterior-posterior direction. For target displacements greater than this, D-95% decreased rapidly.
Conclusions: Targets moving in excess of 5 mm outside the margin can cause significant changes to the target. D-95% decreased by up to 20% with target motion 10 mm outside the margin, with underdosing primarily limited to the target periphery. Multi-fractionated treatments were found to exacerbate target under-coverage. Margins several millimeters smaller than the maximum target displacement provided acceptable motion protection, while also allowing for reduced normal tissue morbidity.

• 出版日期2014-2-5