Highlights
- •End-to-end tests in a dynamic respiratory thorax phantom revealed dose deviations up to 10%.
- •Largest deviations were observed for the smallest 1 cm diameter target.
- •Deviations were not highlighted by classical quality controls.
- •Calculations algorithms tend to underestimate the dose.
Abstract
Purpose
The aim of this study is to perform patient quality controls and end-to-end tests
for stereotactic VMAT lung treatment plans and to investigate the influence of various
parameters on the results.
Method
18 plans were defined by an experimental design methodology to cover a large variety
of stereotactic VMAT lung treatments including different doses per fraction, target
diameters, target movements and respiratory parameters. Plans were first controlled
using portal dosimetry and a homogeneous static cylindrical phantom. End-to-end tests
were then performed in a dynamic respiratory thorax phantom. Measurements were conducted
with ionization chamber and films. Calculations were performed with the AcurosXB and
AAA algorithms in 6 FFF.
Results
Portal dosimetry gave excellent gamma pass rates (greater than 97.1 %) and dose deviations
between measurement and calculations in a homogeneous static phantom were smaller
than 2 %. The methodology followed for comparing calculated and measured doses in
a moving target was validated in static fields (largest deviation smaller than 2 %).
End-to-end tests showed mean deviations of 1.9 %, 3.3 % and 6.6 % for the 3, 2 and
1 cm diameter’s target respectively. Deviations increased for larger movements for
the 1 cm lesion.
Conclusion
End-to-end tests revealed that stereotactic VMAT lung treatment plans for moving targets
can be delivered within 5 % for 3 and 2 cm diameter targets and amplitudes up to 1.5 cm.
The AcurosXB and AAA algorithms however tend to underestimate the dose to the target.
Even with satisfactory patient quality controls like portal dosimetry, extra care
should be taken for GTV lesions smaller than 2 cm.
Keywords
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Article info
Publication history
Published online: February 17, 2023
Accepted:
February 13,
2023
Received in revised form:
January 9,
2023
Received:
November 14,
2022
Identification
Copyright
© 2023 Associazione Italiana di Fisica Medica e Sanitaria. Published by Elsevier Ltd. All rights reserved.
