ESTRO 36 Abstract Book

S229

ESTRO 36 2017

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Antwerpen, Belgium

Brainlab AG- Feldkirchen- Germany, R&D RT Motion

Management, Munich, Germany

University Hospitals Leuven, Department of Radiation

Oncology, Leuven, Belgium

Babes Bolyai University, Faculty of Physics, Cluj-

Napoca, Romania

Purpose or Objective

Dynamic Wave Arc (DWA) is a system-specific non-

coplanar arc technique that combines synchronized

gantry-ring rotation with D-MLC optimization. This paper

presents the clinical workflow, quality assurance program,

and reports the geometric and dosimetric results of the

first patient cohort treated with DWA.

Material and Methods

The RayStation TPS was clinically integrated on the Vero

SBRT platform for DWA treatments. The main difference

in the optimization modules of VMAT and DWA relates to

angular spacing, where the DWA optimization algorithm

does not consider the gantry spacing, but only the

Euclidian norm of the ring and gantry angle. To support

DWA deliveries, the Vero system required some additional

upgrades: an MLC secondary feedback unit upgrade

allowing faster dynamic MLC leaf movement of up to 4

cm/s at isocenter level, and a machine controller offering

gantry-ring synchronous rotations.

The first 15 patients treated with DWA represent a broad

range of treatment sites: breast boost, prostate, lung

SBRT and bone metastases, which allowed us to explore

the potentials and assess the limitations of the current

site-specific DWA template solution. Table 1 provides

further information for each patient case including the

corresponding DWA plan information, while Figure 1

presents the most common used DWA trajectories. For the

DWA verification a variety of QA equipment was used,

from 3D diode array to an anthropomorphic end-to-end

phantom. The geometric accuracy of each arc was verified

with an in-house developed method using fluoroscopy

images.

Results

The average beam-on delivery time was 3min, ranging

from 1.22min to 8.82min. The average

(3%,3mm) passing

rate for film measurements was 97.0 ±1.6% (range from

93.3 to 98.8%), while the Delta

measurements presented

an average

(2%,2mm) of 97.7±1.4% (range from 95.3 to

99.6%) respectively. The average isocentre point dose

ratio was 99.9±1.2% (range from 98.0 to 102.8%). For the

lung SBRT verifications with the CIRS phantom, an average

local

of 97.0±1,0% and 93.1±2.0% was obtained during

the coronal and sagittal film analysis, whereas the average

isocentre point dose ratio was 100.0±1.4%. An overall

mean gantry-ring geometric deviation of 0.04° ± 0.46° and

0.19° ± 0.26° was obtained, respectively.

Conclusion

DWA has been successfully added to the non-coplanar

rotational IMRT techniques’ arsenal, allowing additional

flexibility in dose shaping while preserving dosimetrically

robust delivery. In a short period of time, it has become a

standard treatment technique on the Vero system in our

department.

OC-0440 Characterization and clinical evaluation of a

novel CT reconstruction to derive electron densities

B. Van der Heyden

, M. Ollers

, C. Loon Ong

, F.

Verhaegen

, W. Van Elmpt

School for Oncology and Developmental Biology-

Maastricht University Medical Centre, Department of

Radiation Oncology MAASTRO- GROW, Maastricht, The

Netherlands

Purpose or Objective

Radiotherapy dose calculations are almost exclusively

performed on CT images. In a clinical workflow, the

Hounsfield Units (HU) are converted into electron density

(ED) by using a CT to ED conversion curve calibrated for a

typically fixed tube potential (e.g. 120 kV). Recently, a

novel CT image reconstruction algorithm (DirectDensity

Siemens Healthcare GmbH, Germany) was developed that

directly reconstructs the ED, independent of the tube

potential of the CT scanner. This allows the elimination of

a conversion curve for each tube potential. Our study

describes the accuracy in terms of dose calculation of the

reconstruction

algorithm

based

phantom

measurements and shows the application in a clinical

radiation therapy workflow for different tube potentials.

Material and Methods

The accuracy of the novel reconstruction algorithm to

derive ED was validated in a Gammex RMI 467 phantom

(Gammex, USA) using different tissue mimicking inserts.