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For each dynamic beam delivery the TrueBeam system
also produces a single log of the main system parameters
in a trajectory log text file. The TrueBeam Log Viewer
application can list these parameters versus time for user-
selected accelerators and data interval.
All lists can be sorted with respect to any column, non-
clinical events can be ignored, events not matching a user-
selected main fault code or fault description string can be
ignored, and all lists can be exported to Excel for further
analysis.
Results
Sorting the list of events with respect to the main fault
code provides a fast overview of the number faults for
each fault type and accelerator, facilitating an easy
prioritization of faults (see figure 1). In addition,
treatment plan details and mechanical axes for each event
(for example beam energy, the number of monitor units,
the patient ID, and the gantry angle) are valuable for the
identification of the root cause of the corresponding fault.
A more detailed insight into the root cause of a fault can
be gained by analyzing node records of the corresponding
event in Excel. An example of a node record for a gantry
fault is shown in figure 2. Also trending of the main system
parameters from the trajectory log text files with Excel is
a strong troubleshooting tool.
Conclusion
The TrueBeam Log Viewer application is an efficient tool
both for obtaining an overview of existing faults and for
identification of the root cause of faults. In our clinic the
application has provided a much more substantiated
prioritization of service tasks and faster identification of
the root cause of faults. Varian has no service tools with
this capability.
EP-1738 Performance of a new EPID panel and
opportunities for a fast MV-CBCT acquisition.
C. Kennedy
1
, C. Ling
2
, R. Scheuermann
1
, D. Mihailidis
1
, J.
Metz
1
1
University of Pennsylvania, Radiation Oncology,
Philadelphia, USA
2
Varian Medical Systems, Reserach and Development,
Palo Alto- CA, USA
Purpose or Objective
To study the performance, image quality and clinical
potential of a novel fast MV-CBCT panel mounted on a
straight-through linac with 6X-FFF (filter-free) beam.
Material and Methods
A prototype MV imager is mounted in-line with the linac
at 154 cm source-to-imager distance. MV-CBCT imaging is
performed with 28 cm fixed width (projected at isocenter-
100 cm) and variable field length (up to 26 cm max) FOV,
200º arc, 15 sec rotation time, at 5MU and 10MU dose
levels. Images of a Catphan® 604 phantom are analyzed in
terms of noise, uniformity, spatial and contrast resolution,
and contrast linearity. The results are compare with those
from Truebeam kV-CBCT imager, and potentially, a
Tomotherapy MV-CT imager, all benchmarked to
diagnostic CT scanner images. Imaging dose will also be
assessed for completeness of testing of the MV-CBCT
system.
Results
The uniformity and noise of the MV-CBCT was acceptable
but not as good relative to diagnostic CT and kV-CBCT,
with variation of 32HU from the center to the
periphery. Spatial resolution is shown in Fig. 1 with
3lp/mm for 5MU and 4lp/mm for 10MU dose levels, as
compared to 7lp/mm for both kV-CBCT and diagnostic
CT. The low contrast resolution of the MV-CBCT was >>
1%, compared to 1.0% and 0.5% for kV-CBCT and diagnostic
CT. Contrast linearity and sensitometry is shown in Fig. 2,
with the MV-CBCT (and 10MU dose level) being the
modality that deviates especially for higher density
objects like Acrylic, Delrin and Teflon (green data
points). Additional tests with varying field length (small,
medium and max length) for the MV-CBCT did not show
any correlation and/or improvement to the image quality
results. Imaging dose will be assessed and presented
based on absolute beam output calibration with a 6cc ion
chamber and OSLDs. The Tomotherapy data and analysis
is underway for comparisons.