IROC-Houston Site
Visit Data Aggregation
What site visits can tell us about our machines
J. Kerns, P. Alvarez, D. Followill, J. Lowenstien, A. Molineu, P. Summers, S. Kry
-Department of Radiation Physics, The University of Texas MD Anderson Cancer
Center
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Introduction
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Accurate experimental data for treatment planning system commissioning &
MC models
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Some reference data out there (e.g. GBD), but limited in scope
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Publish data collected by IROC for community use (TPS commissioning, site
visit preparation, matching different machine classes)
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IROC Site Visit
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What is it?
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IROC physicist visits institution
QA program reviewed against TG-142
Linac mechanicals, dosimetric parameters measured
Report & recommendations given
Dosimetric Point Measurements
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PDD (10x10cm2; dmax, 5, 10, 15, 20 cm)
Jaw Output Factors (30x30, 20x20, 15x15, 6x6 cm2)
MLC Output Factors (6x6, 4x4, 3x3, 2x2 cm2)
Off-Axis Factors (5, 10, 15 cm)
Wedge Factors
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The Data
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Measurements
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Exradin A12 (Farmer)
Exradin A16 (micro-chamber)
30x30x30cm3
Pushed to database
Aggregation
 1998-present chosen; Matlab used for
sorting & calculation
 Data separated by
 Machine
 Vendor
 Energy
 Machine class
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Varian, 6 MV, ~400 machines
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Machine Classes
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TrueBeam Flat
TrueBeam
TrueBeam FFF
TrueBeam
Trilogy SRS
Trilogy
Develop common classes from individual
machines
21EX
21EXD
23EX
Base Class
21iX
23iX
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Data grouped by name, ANOVA ran on
all parameters for:
 Statistical Significance (p<0.05)
&
 Clinical Significance (Δ>0.3%)
iX
Varian 6 MV
Trilogy
2300
2300+
2300C
2300CD
2100CD
2100CD
2100C
2100C
600C
600C+
600CD
6EX
6EX
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Percent Depth Dose
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Matching 2100 with 6EX or Truebeam could be an issue
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Jaw Output Factors
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Serious challenges to match different classes
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MLC Output Factors
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MLC factors are difficult to acquire; IROC data are consistent
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Off-Axis Factors
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Off-Axis factors consistent with class
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So What?
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You can use this data
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It’s comprehensive
Statistical metrics to understand relation to everyone else
Discuss whether multiple machine classes are an option
Why 1 model might not work for multi-class institutions
Find holes in TPS or input data
TPS-to-machine match is most important
 Sanity check
 TPS or machine commissioning
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Thank You! Questions?
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Normal Data?
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Multiple physicists; multiple
techniques?
Lilliefors test (normality; returns
p-value) failed everywhere for all
parameters
Quartile-quartile (Q-Q) plot shows
very normal data with deviations
at the tails
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