Highlights
- •We measured the RPLD dose responses for TomoTherapy, CyberKnife, and FFF linac units.
- •We determined the correction factors for each of these types of units.
- •We analysed the four-year audit results obtained with these factors.
- •The average difference between the measured and hospital-stated doses was <1%.
- •The RPLD is a suitable dosimetry audit tool for these modern treatment units.
Abstract
Purpose
We experimentally determined the radiophotoluminescent glass dosimeter (RPLD) dose
responses for TomoTherapy, CyberKnife, and flattening-filter-free (FFF) linear accelerator
(linac) outputs for dosimetry audits in Japan.
Methods
A custom-made solid phantom with a narrow central-axis spacing of three RPLD elements
was used for output measurement to minimise the dose-gradient effect of the non-flattening
filter beams. For RPLD dose estimation, we used the ISO 22127 formalism. Additional
unit-specific correction factors were introduced and determined via the measured data.
For TomoTherapy (7 units) and CyberKnife (4 units), the doses were measured under
machine-specific reference fields. For FFF linac (5 units), in addition to the reference
condition, we obtained the field-size effects for the range from 5×5 cm to 25×25 cm.
Results
The correction factors were estimated as 1.008 and 0.999 for TomoTherapy and CyberKnife,
respectively. For FFF linac, they ranged from 1.011 to 0.988 for 6 MV and from 1.011
to 0.997 for 10 MV as a function of the side length of the square field from 5 to
25 cm. The estimated uncertainties of the absorbed dose to water measured by RPLD
for the units were 1.32%, 1.35%, and 1.30% for TomoTherapy, CyberKnife, and FFF linac,
respectively. A summary of the dosimetry audits of these treatment units using the
obtained correction factors is also presented. The average percentage differences
between the measured and hospital-stated doses were <1% under all conditions.
Conclusion
RPLD can be successfully used as a dosimetry audit tool for modern treatment units.
Keywords
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Article info
Publication history
Published online: June 29, 2021
Accepted:
June 4,
2021
Received in revised form:
May 11,
2021
Received:
March 12,
2021
Identification
Copyright
© 2021 Associazione Italiana di Fisica Medica. Published by Elsevier Ltd. All rights reserved.
