Transcript Implementing RapidArc into clinical routine - Ra

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
Specific tests for RA implementation
I. Machine QA
II. TPS QA
III.Performance assessment of the RA
optimization algorithm (PRO8.9)
(artificial cases)
IV. Patient-specific QA (clinical and
artificial cases)
i.
ii.
Phantom QA: GafChromic EBT film/
Delta4/Seven29+Octavius/
Portal dosimetry
Med Phys;38(9):5146-66, 2011.
RapidArc Workshop 2012, Aarhus, Denmark
Maria Sjölin/ 27-01-2012
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 accuracy
Tests were performed with:
GafChromic EBT film
+solid water
+EPSON scanner
+VERISOFT FILMSCAN (v2.1)
StarCheck + BeamAdjust
+inclinometer
(+MATLAB)
Seven29 + Verisoft
+ inclinometer
(+MATLAB)
RapidArc Workshop 2012, Aarhus, Denmark
Maria Sjölin/ 27-01-2012
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
RapidArc Workshop 2012, Aarhus, Denmark
Maria Sjölin/ 27-01-2012
Reproduced
correct delivery
Reference image
+introduced error of 3
deg clockwise delay
Reference image
+2 deg smoothening effect
around the actual ctrlpt
RapidArc Workshop 2012, Aarhus, Denmark
Maria Sjölin/ 27-01-2012
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).
RapidArc Workshop 2012, Aarhus, Denmark
Maria Sjölin/ 27-01-2012
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.
RapidArc Workshop 2012, Aarhus, Denmark
Maria Sjölin/ 27-01-2012
Static field measurements
i.
RapidArc Workshop 2012, Aarhus, Denmark
DLS validation
ii.
Small and/or off-axis
effective opening in
large collimator
iii.
Tongue and groove
Maria Sjölin/ 27-01-2012
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
RapidArc Workshop 2012, Aarhus, Denmark
Maria Sjölin/ 27-01-2012
Thanks for listening!
RapidArc Workshop 2012, Aarhus, Denmark
Maria Sjölin/ 27-01-2012