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AAPM2019 SRS MapCheck v2

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Characterization and Validation of SRS MapCheck for Patient Specific QA On
CyberKnife M6
Poster · July 2019
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10 authors, including:
David Parsons
Yulong Yan
University of Texas Southwestern Medical Center
University of Texas Southwestern Medical Center
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Xuejun Gu
University of Texas Southwestern Medical Center
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Characterization and validation of SRS MapCheck for patient specific QA on CyberKnife M6
David
1
Parsons ,
Chuxiong
1
Ding ,
2
Tirpak ,
1
Zhao ,
1
Chiu ,
1
Reyonlds ,Yang
1
Park ,
Lena
Bo
Tsuicheng
Robert
Yulong
Steve
1Department of Radiation Oncology, University of Texas Southwestern Medical Center, Dallas, TX
2Sun Nuclear Corporation, Melbourne, FL
Introduction
Figure 1: SRS
and
StereoPHANTM.
To date, SRS
has yet to be
released for CyberKnife (CK) patient
specific QA, which is often conducted with
film and chamber. SRS MapCheckTM will
eliminate the film process and will improve
confidence in the QA due to the 1013 diode
dose measurements made compared to
the single ion chamber. In this work, we
characterize SRS MapCHECKTM diode
array and validate a workflow for using this
device for CK patient specific QA.
Figure 2 illustrates the
workflow of calibrating
SRS MapCHECKTM and
the process of creating
a QA plan in the
treatment
planning
system (TPS). Briefly,
this process begins by
calibrating the diode
array (in absence of the
StereoPHANTM). This is
followed by a phantom
correction on CK using
a 60mm cone at
source-to-detector
distance
(SDD)
of
80cm.
Next
the
Figure 2: Overview of SRS MapCheckTM calibration and QA plan creation.
phantom is CT scanned
and imported into the TPS, and a QA phantom template made with the fiducials marked.
This is used to create absolute dose calibration plans. A similar process is used for QA
plan creation with the added step of exporting the dose volume and XML report
(equivalent of the DICOM RT Plan) for aligning the TPS dose volume to SRS
MapCheckTM.
Central axis diode response has been evaluated for varying dose rate (SDD) and
rotation of the detector. Finally, 30 previously treated patients on CK were evaluated
using SRS MapCheckTM. Central axis dose and gamma with a criteria of 2% dose
(global) and 1 mm with a 10% threshold were used.
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(a)
Figure 3b shows the angular
response of the array, which underresponds by approximately 2% when
approaching 90o. Figure 3c highlights
the over- and under-reponse of the
central axis diode for varying SDD (an
approximately 5x5cm2 field on the
array was used for each SDD). For
comparison, a head and body path on
CK range from 64 to 90 cm and 80 to
120 cm, respectively, at our clinic.
SRS MC
Materials & Methods
Radiation Oncology
1
Jiang
and Xuejun
1
Gu
Results and Discussion
MapCHECKTM
MapCHECKTM
1
Yan ,
(b)
(c)
Figure 3: (A) SRS MapCHECKTM on CyberKnife. (B) Angular and (C) dose rate response.
Measured
Additionally, output factor was investigated and found to vary by
approximately -0.7% and 0.9% at fields of 7x7mm² and 70x70mm².
Figure 7 shows the gamma analysis for 30 previously treated patients on
CK using SRS MapCheckTM. The mean gamma (absolute dose,
2%/1mm, 10% threshold) pass rates were 97.2±1.9%, 98.1±2.3% and
94.4±5.8% for the MLC, iris, and fixed collimators, respectively, over all
paths. Corresponding measured central axis doses were -1.6±0.7%, 1.8±1.5%, and -0.4±4.7% from the planned doses. We hypothesis that
this is most likely due to angular under-response; output factor errors
over small field segments, or both.
Figure 5: End-to-end test of a 60 mm static cone.
SRS MC
Measured
Figure 6: Example Thalamus legion patient QA with SRS
MapCHECKTM.
Figure 7:
MapCHECKTM gamma (2%/1mm) results for 30 patients on
CyberKnife M6 using MLC, Iris and Cone for both head and body paths.
Conclusions
The use of SRS-MC has been characterized and validated for patient specific QA on CyberKnife for a variety of clinical plans.
The results show that SRS-MC is well suited for this task.
AAPM 2019 • San Antonio, TX
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