Machine-specific QC in Aarhus using EPID Mai-Britt K. Jørgensen, Lone Hoffmann, L.P. Muren, Lars H. Præstegaard, Rune Hansen, Jørgen B.B. Pedersen, Maria F. Jensen Aarhus University Hospital Department of Medical Physics

Rutine QC 2 ▪ IMRTVMAT Machine specificSweeping gap Picket fence (PF) Sweeping gap Picket fence (PF) Dose rate versus gantry speed (DRGS) Dose rate versus MLC speed (DRMLC) Patient specificPDI (Delta4) (PTW729 array) PDI (Delta4)

Picket fence, PF For every MLC and gab…  Position:  Relative rotation of EPID and collimator  Intensity (”width”): 3 ▪

PF: ex. ”Eye test”

PF: ex. Deviation in position, tolerance ±0.3mm 5 ▪

PF: ex. Deviation in intensity, tolerance ±300

PF: ex. ”Eye test version 2”

PF: In total ~30 test on each accelerator, one every month

Dose rate vs. gantry speed, DRGS 9 ▪

DRGS: ex. typical deviation

DRGS: ex. cable issue 11 ▪

DRGS: In total ~30 test on each accelerator, one every month

Dose rate vs. MLC speed, DRMLC 13 ▪

DRMLC: ex. segment 4 DR120, 0.4cm/s 14 ▪

DRMLC: ex. segment 2 DR600, 2.4cm/s

DRMLC: ex. segment 4 DR120, 0.4cm/s segment 1 DR480, 1.6cm/s

DRMLC: In total ~30 test on each accelerator, one every month

Time consumption  Measurements:~10 min  Analysis (home-made software):~1 min  Total:~11 min 18 ▪

Effect of chain adjustments on the DRGS and DRMLC tests  Mehtod  3 DRGS and 3 DRMLC test with a loose chain  3 DRGS and 3 DRMLC test with a thight chain  Result, comparing loose and thight chain  DRGS: Standard deviation was unchanged  DRMLC: Std 0.6 (loose) -> 0.2 (tight) 19 ▪

Loose chain: unstable characteristic

Tight chain: Stable characteristic

Discussion  Deviations in PF are covered in next, next session  Deviations in DRGS and DRMLC  Chain adjustments have an effect on DRGS and DRMLC test, but it does not solve everything  Cable issues  Beam adjustments?  For more information on the calculations and tolerances: Med. Phys. 38, 1425 (2011); 22 ▪