Highlights
- •There is a lack of efficient integrated machine quality assurance tools when third-party systems are associated to the linac.
- •A basic cone alignment test was developed for SRS cones.
- •A Winston-Lutz test variant is suggested for the smallest cones.
- •A cone alignment test is suggested as a pre-treatment QA for SRS treatments.
Abstract
Purpose
The Varian TrueBeam STx linac can be equipped with BrainLAB stereotactic cones and
ExacTrac imaging system for SRS treatments. However, these two third-party systems
lack integration in a self-performance diagnosis tool dedicated to the SRS platform.
The aim of this work was to design and automate essential geometric tests considering
the complete set of cones with diameter range from 4 to 15 mm.
Methods
EPID-based tests were focused on the cone alignment, the radiation isocentricity and
the isocenters congruence. Images acquired with or without the BrainLAB pointer were
analysed using the Hough transform and morphological filtering operations, after assessment
of the algorithm accuracy using simulated images. The new Machine QA program was experimented
over one year.
Results
A subpixel resolution of 0.02 mm was found for the circular-field center detection
algorithm. The tests results did not depend on the pointer location. The maximum deviations
reported were in accordance with the AAPM SRS guidelines. The accurate localization
of the linac radiation isocenter allowed for guidance of the ExacTrac calibration.
A misalignment reaching 0.2 mm was measured for all cones but one, highlighting the
benefit of systematizing this control before each patient SRS treatment.
Conclusion
An effective in-house QA program dedicated to SRS cones was developed to supplement
the standard machine performance check on our mixed SRS platform. Specific geometric
tests even include the smallest 4-mm cone, which could be of great interest for future
clinical indications such as the radiosurgery of functional disorders.
Keywords
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Article info
Publication history
Published online: February 18, 2022
Accepted:
February 12,
2022
Received in revised form:
January 12,
2022
Received:
October 14,
2021
Identification
Copyright
© 2022 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.
