Motion induced interplay effects for VMAT radiotherapy

The purpose of this study was to develop a method to simulate breathing motion induced interplay effects for volumetric modulated arc therapy (VMAT), to verify the proposed method with measurements, and to use the method to investigate how interplay effects vary with different patient- and machine s...

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Bibliographic Details
Published in:Physics in medicine & biology 2018-04, Vol.63 (8), p.085012-085012
Main Authors: Edvardsson, Anneli, Nordström, Fredrik, Ceberg, Crister, Ceberg, Sofie
Format: Article
Language:English
Subjects:
Annan fysik
breathing motion
Clinical Medicine
delivery
dose distributions
dosimetric impact
Engineering
Fysik
imrt treatments
interplay effects
intrafractional motion
Klinisk medicin
lung
Medical and Health Sciences
Medicin och hälsovetenskap
moving targets
Natural Sciences
Naturvetenskap
Nuclear Medicine & Medical Imaging
organ motion
Other Physics Topics
Physical Sciences
radiation-therapy
Radiologi och bildbehandling
Radiology
Radiology, Nuclear Medicine and Medical Imaging
radiotherapy
RapidArc
stereotactic body radiotherapy
VMAT
volumetric modulated arc
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Summary:The purpose of this study was to develop a method to simulate breathing motion induced interplay effects for volumetric modulated arc therapy (VMAT), to verify the proposed method with measurements, and to use the method to investigate how interplay effects vary with different patient- and machine specific parameters. VMAT treatment plans were created on a virtual phantom in a treatment planning system (TPS). Interplay effects were simulated by dividing each plan into smaller sub-arcs using an in-house developed software and shifting the isocenter for each sub-arc to simulate a sin6 breathing motion in the superior-inferior direction. The simulations were performed for both flattening-filter (FF) and flattening-filter free (FFF) plans and for different breathing amplitudes, period times, initial breathing phases, dose levels, plan complexities, CTV sizes, and collimator angles. The resulting sub-arcs were calculated in the TPS, generating a dose distribution including the effects of motion. The interplay effects were separated from dose blurring and the relative dose differences to 2% and 98% of the CTV volume (ΔD98% and ΔD2%) were calculated. To verify the simulation method, measurements were carried out, both static and during motion, using a quasi-3D phantom and a motion platform. The results of the verification measurements during motion were comparable to the results of the static measurements. Considerable interplay effects were observed for individual fractions, with the minimum ΔD98% and maximum ΔD2% being  −16.7% and 16.2%, respectively. The extent of interplay effects was larger for FFF compared to FF and generally increased for higher breathing amplitudes, larger period times, lower dose levels, and more complex treatment plans. Also, the interplay effects varied considerably with the initial breathing phase, and larger variations were observed for smaller CTV sizes. In conclusion, a method to simulate motion induced interplay effects was developed and verified with measurements, which allowed for a large number of treatment scenarios to be investigated. The simulations showed large interplay effects for individual fractions and that the extent of interplay effects varied with the breathing pattern, FFF/FF, dose level, CTV size, collimator angle, and the complexity of the treatment plan.
ISSN:0031-9155
1361-6560
1361-6560
DOI:10.1088/1361-6560/aab957