Implementing RapidArc into clinical routine: A comprehensive program from machine QA to TPS...
-
date post
20-Dec-2015 -
Category
Documents
-
view
217 -
download
2
Transcript of Implementing RapidArc into clinical routine: A comprehensive program from machine QA to TPS...
Implementing RapidArc into clinical routine:
A comprehensive program from machine QA to TPS validation and patient QA
Maria Sjölin
Department of Oncology, Division of Radiophysics,
Copenhagen University hospital, 2730 Herlev
Maria Sjölin/ 27-01-2012RapidArc Workshop 2012, Aarhus, Denmark
Specific tests for RA implementation
I. Machine QAII. TPS QAIII. Performance assessment of the RA
optimization algorithm (PRO8.9) (artificial cases)
IV. Patient-specific QA (clinical and artificial cases)
i. Phantom QA: GafChromic EBT film/ Delta4/Seven29+Octavius/
ii. Portal dosimetry
Med Phys;38(9):5146-66, 2011.
Maria Sjölin/ 27-01-2012RapidArc Workshop 2012, Aarhus, Denmark
Machine QA (I.)
Test of the delivery beyond its clinically used limits (at the machine)
A number of tests were developed to focus on angular accuracyTests were performed with:
GafChromic EBT film+solid water+EPSON scanner+VERISOFT FILMSCAN (v2.1)
StarCheck + BeamAdjust+inclinometer(+MATLAB)
Seven29 + Verisoft+ inclinometer(+MATLAB)
Maria Sjölin/ 27-01-2012RapidArc Workshop 2012, Aarhus, Denmark
Examples of machine QA tests
Static /Dynamic MLC Twinkle 2 deg narrow angular sectors, 1 mm
wide static/dynamic central gap → minimal gantry speed
38 deg dose-less sectors → maximum gantry speed
Different MUs were delivered to check dose delivery during acceleration/deceleration for comparison:
Increasing the amount of MU → the gantry will slow down!
The test can also be performed with constant gantry speed
Introduced errors The dose rays were shifted 1, 2, and 3
deg → simulate a slow response
The rays were broadening by 1,2, and 3 deg
Maria Sjölin/ 27-01-2012RapidArc Workshop 2012, Aarhus, Denmark
Reproduced correct delivery
Reference image +introduced error of
3 deg clockwise delay
Reference image +2 deg smoothening
effect around the actual ctrlpt
Maria Sjölin/ 27-01-2012RapidArc Workshop 2012, Aarhus, Denmark
TPS QA (II.)
For RapidArc, the calculation of the dynamic source in the TPS is approximated by summing multiple static gantry,
dynamic MLC fields using the AAA algorithm(Anisotropic Analytical Algorithm).
Maria Sjölin/ 27-01-2012RapidArc Workshop 2012, Aarhus, Denmark
The accuracy of the dose calculation is challenged by:
The use of multiple small and off axis openings in relatively large collimator openings…
Leaf-pairs with nearly closed MLC tips commonly… (DLS parameter)
Highly asynchronous leaf movement… (Tongue and groove)
An example of a beams-eye-view sequence for four control points, with a gantry spacing of 2 degrees.
Maria Sjölin/ 27-01-2012RapidArc Workshop 2012, Aarhus, Denmark
Static field measurements
i. DLS validation
ii. Small and/or off-axis effective opening in large collimator
iii. Tongue and groove
Maria Sjölin/ 27-01-2012RapidArc Workshop 2012, Aarhus, Denmark
Examples of line profiles-3 mm leaf-gap
Ionization chamber measurements agree within 2 % with the calculated absolute dose in the center of field opening (4x4 cm)
Satisfactory agreement between dose-peaks under leaf tips
Using a high resolution (0.3 mm) fluence improves the results
Maria Sjölin/ 27-01-2012RapidArc Workshop 2012, Aarhus, Denmark
Thanks for listening!