Abstract
The objective of the study is to verify the dose delivered on helical tomotherapy
based on treatment plan with varying virtual bolus (VB) thickness. The target was
localized on the ArcCHECK image by 3 mm margin from the phantom surface. The dimension
of target, which includes the ArcCHECK's detectors, with the 4.0 cm width and length
12.0 cm along the phantom The 5 treatment plans were generated, 1 plan without VB
application (NoVB) and the 4 plans with varying of VB thickness on the phantom surface
by 0.5 cm (VB0.5), 1.0 cm (VB1.0), 1.5 cm (VB1.5), and 2.0 cm (VB2.0), in treatment
planning but absent during irradiation. For measurement analysis, the ionization chamber
and the ArcCHECK detectors were used for point dose and dose distribution by investigating
the percentage of dose difference and the gamma passing rate. The VB thickness 0.5,
1.0 and 1.5 cm showed acceptable value with less than 2% for dose difference by 0.37%
(VB0.5), -0.11% (VB1.0) and -0.37% (VB1.5) at the center of ArcCHECK. The accuracy
of dose distribution showed an acceptable gamma passing rate of 99.8% (VB0.5), 100%
(VB1.0), and 90.2% (VB1.5) for gamma criteria by 3%/3mm for absolute dose analysis.
However, the gamma passing rate of VB2.0 down to 71.2% of absolute mode for gamma
criteria by 3%/3mm. The treatment plans with VB thickness less than 15 mm deliver
doses that are comparable to treatment plans without virtual bolus based on gamma
analysis. However, the deviation showed a trend increasing when VB thickness increased.
The VB2.0 was not acceptable for point dose and dose distribution verification by
more than 2% dose difference and less than 90% of gamma passing rate.
Keywords
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Article info
Publication history
Published online: October 25, 2022
Accepted:
September 16,
2022
Received in revised form:
September 9,
2022
Received:
July 27,
2022
Footnotes
Author responsible for statistical analysis: Wannapha Nobnop, Ph.D
This study was exemption approved by the Institutional Review Board of the Faculty of Medicine Chiang Mai University (study code RAD-2564-08212/Research ID: 8212).
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Copyright
© 2022 American Association of Medical Dosimetrists. Published by Elsevier Inc. All rights reserved.
