1. www.regionmidtjylland.dk 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

2. Rutine QC 2 ▪ www.regionmidtjylland.dk 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)

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

4. PF: ex. ”Eye test”

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

6. PF: ex. Deviation in intensity, tolerance ±300

7. PF: ex. ”Eye test version 2”

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

9. Dose rate vs. gantry speed, DRGS 9 ▪ www.regionmidtjylland.dk

10. DRGS: ex. typical deviation

11. DRGS: ex. cable issue 11 ▪ www.regionmidtjylland.dk

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

13. Dose rate vs. MLC speed, DRMLC 13 ▪ www.regionmidtjylland.dk

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

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

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

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

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

19. 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 ▪ www.regionmidtjylland.dk

20. Loose chain: unstable characteristic

21. Tight chain: Stable characteristic

22. 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 ▪ www.regionmidtjylland.dk