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

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Radiation Oncology

, 9:46

Radiation Physics


PurposeIntrafraction 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.

MethodsA 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.

ResultsD95% 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, D95% decreased rapidly.

ConclusionsTargets moving in excess of 5 mm outside the margin can cause significant changes to the target. D95% 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.


KeywordsIMRT Motion Step-and-shoot Lung Dosimetry Electronic supplementary materialThe online version of this article doi:10.1186-1748-717X-9-46 contains supplementary material, which is available to authorized users.

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Author: Benjamin J Waghorn - Amish P Shah - Justin M Rineer - Katja M Langen - Sanford L Meeks

Source: https://link.springer.com/

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