ESTRO 36 Abstract Book

S280 ESTRO 36 2017 _______________________________________________________________________________________________

torso contains lungs and ribs and is made of materials mimicking human tissue Hounsfield Unit. The lungs are shaped thus to host four water equivalent inserts (WEI) that simulate lung lesions and a fillable QA sphere (QAS) to test reconstruction performances of 4D scanners. Films can be inserted between two WEIs and a specific housing for a diamond detector has been drilled into one WEI. 6 small tin markers have also been included near the fourth WEI to test markers guided tracking procedure. The anterior part of the phantom moves up and down in sync with lungs movements driven by an Arduino programmable board hosted in the caudal phantom portion. Elliptical paths (axes up to 2cm), pre-programmed in the microcontroller, and patient specific respiratory movements, programmable by users, can be chosen on the LCD screen placed on the caudal extremity of the phantom. Preliminary tests were performed to assess Adam usability and its performances in terms of HU, WEI motion repeatability and lungs-to-surface motion correlation. Finally a VMAT plan, to deliver 18Gy to one internal WEI, was planned on an average reconstructed 4DCT data set and delivered to ADAM. Dose was prescribed to 95% of the PTV = ITV (encompassing all motion and delineated on MIP) + 5 mm margin. The delivered dose distribution, measured with a Gafchromic EBT3 film, was overlapped on the WEI to assess moving target dose coverage. Results In Figure 1 ADAM and some internal details, as appear in CT images, are presented.

phases.

Conclusion ADAM demonstrates suitable performances to test instruments and methods used to treat moving lesions. OC-0534 Establishment of patient-specific quality assurance procedure for Dynamic WaveArc delivery technique H. Hirashima 1 , N. Nakamura 1 , Y. Miyabe 1 , N. Mukumoto 1 , M. Uto 1 , K. Nakamura 1 , T. Mizowaki 1 , M. Hiraoka 1 1 Kyoto University Hospital, Department of Radiation Oncology and Image applied Therapy, Kyoto, Japan Purpose or Objective Dynamic WaveArc (DWA) is a novel delivery techniquethat uses the Vero4DRT system (Mitsubishi Heavy Industries [MHI], Ltd., Tokyo, Japan, and Brainlab, Feldkirchen, Germany) for volumetric modulated arc therapy, with continuous non-coplanar delivery. DWA achieves high-dose conformality by optimizing the dose rate, gantry speed, ring speed, and positions of the dynamic multi-leaf collimator (MLC). The purpose of this study was to establish the patient-specific quality assurance (QA) Twenty DWA plans, 10 for brain tumors and 10 for prostate cancer, were created using RayStation version 4.7 (RaySearch Laboratories, Stockholm, Sweden). The prescribed dose for the brain tumor was set as 52.2 Gy at 1.8 Gy per fraction, and that for the prostate tumor was set as 76 Gy at 2 Gy per fraction. The patient-specific QA included the accuracy verification of the measured dose distribution, machine movement, and reconstructed dose distribution. First, absolute dose distributions measured by ArcCHECK (Sun Nuclear Inc, Melbourne, FL) were assessed by using 3%/3 mm global γ-tests for the area receiving more than 10% isodose, based on the AAPM TG119 report. Next, the log files were analyzed to evaluate the accuracy of the machine movement. The log files, including the actual gantry angle, ring angle, MLC position, and monitor unit (MU) were obtained at 50 ms intervals. Root mean square errors (RMSEs) between the planned and actual values in the log files were calculated. Finally, the delivered dose distributions were reconstructed based on the log files. The in-house software was used to load the original DICOM-RT plan file, and searched the actual values at each control point. Thereafter, the in-house software replaced the planned values at each control point with the actual values based on the log file, and then generated a reconstructed DICOM-RT plan file. The reconstructed plan was imported into RayStation, and then recalculated on the planning CT. The originally-planned dose-volumetric indices were compared with the reconstructed ones. Results In the ArcCHECK dosimetry, the means ± standard deviations (SDs) of the γ-pass rates were 97.0% ± 1.2% (range, 94.3%–98.7%) and 98.4% ± 1.0% (range, 96.6%– 99.5%) for the brain and prostate tumors, respectively. In the log file analysis, the RMSEs for the gantry angle, ring procedure for the DWA. Material and Methods

CT acquisitions demonstrate realistic human tissues HU values: -860±37, 77±30, 83±20, 1098±84 respectively for lung, thorax soft tissue, WEI and bone. The absence of artifacts of reconstructed QAS and WEIs in all phases, demonstrate lungs-to-surface motion correlation. Movement tests show a long (20 days) and short-term (30min) amplitude repeatability <1 mm along both axes. In Figure 2 measured dose distribution delivered to a moving target is shown together with the QAS volume measured in static CT and in some 4DCT reconstructed