A virtual simulator in an multivendor radiotherapy department, an overview of the commissioning process Geert Pittomvils, Lobke Mommaerts, Frederic Crop, Leen Paelinck, Tom Vercauteren, Marc Van Eijkeren Ghent University Hospital, department of radiotherapy, Ghent, Belgium

Overview of the selected solution Toshiba Aquillion Large Bore –Bore 90 cm / –Max scan diameter 70 cm A2J horus laser system –SV 5, 4 lateral laser one sagital Elekta Focal Sim workstation (CMS)

Workflows to be tested Export dicom coordinates of reference points to movable lasers CT-simulator to Eclipse/Pinnacle –Dicom 3 verification (NCS 15) CT-simulator –Dicom RT verification (NCS 15, TG 53, TG 66) Monthly QA Protocol (TG 66) Rotational plate linac QA device

Monthly QA protocol overview of some tests Agreement lasers and zero scan plane –Projection of the metal markers of central plane –sub mm accuracy

Agreement lasers and zero scan plane Cranial- caudal, ant- post and posterior is checked OK Adjust left-right

Monthly QA protocol Verification displacement of the lasers (-10,-5,0,5,10 cm for all movable lasers is possible (using horizontal and vertical positions Control of the table pitch (rotation error lasers CT-simulator) –Recording on the scanner of the dicom coordinates (-75mm, -75 mm, 0) (75mm, 75 mm, 0)

Dicom 3 export To focal, to Eclipse, to Pinnacle to Gratis –Using ULF phantom in HFS, HFP, FFS, FFP position (NCS 15) –Dicom origin is passed correctly to Eclipse (X,Y,Z coord) and to Pinnacle only the height is different while table position is not set

Export data to lasers Rotational plate linac QA device is used in vertical an horizontal position and reference points are defined at marker positions for every export possibility (beams, markers, ….) for every patient position HFS, HFP, FFP,FFS and verified visually on the phantom

Dicom RT export Careful set of beams is selected to verify every collimator position (incl. limits), jaw position (incl. limits), gantry position, table position (incl. limits), MLC positions (incl. leaf position limitations: over travel, max. leaf span, leaf gap, interdigitation,………….) Verification of beam isocentrum information Only the collimator rotation limitation of the Varian Linac and the table angle limitations of the linacs could not be set in Focal Sim

Ex. Leaf Gap Elekta Standard MLC Change of linac during simulation, jaw labeling and MLC are changed automatically

Dicom RT-struct export A small circle contour is made around a rod in CMS focal sim and exported to the planning systems A shift of a half pixel (post-right) is observed while exporting to Pinnacle A reduction of the number of points of the contour is observed in Eclipse Focal contour Focal contour exported to Pinnacle Focal contour exported to Eclipse

Dicom RT-struct export CT scan with slice thickness of 2 mm was used as standard data- set V shaped structure is entered by slice by slice contouring, one arm in cranial-caudal direction, one arm at 45° Expansions of 2mm, 2,5+2,5 mm, 3 mm, 3+2 mm are created Similar expansions are created on Eclipse (only integer mm numbers are possible) and Pinnacle Focal sim axial + expansie mm sagitaal coronaal Focal sim

Dicom RT-struct export In cranial caudal direction 3 mm expansion after Dicom RT export becomes –In Pinnacle an expansion of 2 slices, –In Eclipse an expansion of 1 slice and –the expanded RT-struct file transferred from CMS Focal Sim is imported (in Pinnacle and in Eclipse) by an expansion of 1 slice cranially and 2 slices caudally (RT-struct export exports only contours slice by slice) Blue line is the 3 mm expansion in Focal Sim exported to Eclipse the green line is the same expansion in Eclipse Focal sim

Expansion 3 mm + 2 mm in Pinnacle = purple, expansion in Eclipse is red Expansion 3 mm + 2 mm in CMS and exported to Pinnacle/Eclipse is in skincolor Pinnacle Eclipse Pinnacle

RT-struct Expansion of an expansion (2+3 mm) can result in errors of 3 mm for oblique orientations for the V shaped structure Every virtual simulation workstation every planning system has his own way for representation a contour in one slice –A disk with a height of the slice thickness –A double pyramid contained within that one slice –………… Expansion with a non integer number of mm in slice thickness can result in different expanded contours This is important when creating a large number of small structures (dose painting, integrated boost, stereotactic irradiations) and when using different working platforms using DICOM RT import and DICOM RT export between different modalities (CT-simulator, Cone Beam CT on linac, Treatment Planning system)

Dicom RT structure expansion of a U like structure (blue line) until the top closes CMS Focal fills the central opening, eclipse and Pinnacle are handling this problem correctly