Highlights
- •Patient specific estimation of interplay effects improves ahead of treatment.
- •Investigated a novel software allowing virtual phantom motion during beam delivery.
- •Developed in-house software to generate user defined breathing traces.
- •Physically moved the 3D dose measuring phantom by programmed couch for validation.
- •Investigated interplay for 14 Lung VMAT SABR plans and various breathing traces.
Abstract
Purpose
In lung SABR, interplay between target motion and dynamically changing beam parameters
can affect the target coverage. To identify the potential need for motion-management
techniques, a comprehensive methodology for pre-treatment estimation of interplay
effects has been implemented.
Methods
In conjunction with an alpha-version of VeriSoft and OCTAVIUS 4D (PTW-Freiburg, Germany),
a method is presented to calculate a virtual, motion-simulated 3D dose distribution
based on measurement data acquired in a stationary phantom and a subsequent correction
with time-dependent target-motion patterns. In-house software has been developed to
create user-defined motion patterns based on either simplistic or real patient-breathing
patterns including the definition of the exact beam starting phase. The approach was
validated by programmed couch and phantom motion during beam delivery.
Five different breathing traces with extremely altered beam-on phases (0 % and 50 %
respiratory phase) and a superior-inferior motion altitude of 25 mm were used to probe
the influence of interplay effects for 14 lung SABR plans. Gamma analysis (2 %/2mm)
was used for quantification.
Results
Validation measurements resulted in >98 % pass rates. Regarding the interplay effect
evaluation, gamma pass rates of <92 % were observed for sinusoidal breathing patterns
with <25 number of breaths per delivery time (NBs) and realistic patterns with <18
NBs.
Conclusion
The potential influence of interplay effects on the target coverage is highly dependent
on the patient’s breathing behaviour. The presented moving-platform-free approach
can be used for verification of ITV-based treatment plans to identify whether the
clinical goals are achievable without explicit use of a respiratory management technique.
Keywords
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Article info
Publication history
Published online: December 16, 2022
Accepted:
November 23,
2022
Received in revised form:
September 18,
2022
Received:
January 13,
2022
Identification
Copyright
© 2022 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.
