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!