Commissioning. Basic machine performance MLC Dose rate control Gantry speed control End-to-end tests

Transcription

1 Acknowledgements David Shepard, Ph.D. Daliang Cao, Ph.D. Muhammad K. N. Afghan, Ph.D. Jinsong Ye, M.S. Tony P. Wong, Ph.D. Fan Chen, Ph.D. Min Rao, Ph.D. Vivek Mehta, M.D. Igor Gomola, Ph.D. David Housley Gerry Vantellingen

2 Commissioning Basic machine performance MLC Dose rate control Gantry speed control End-to-end tests

3 Picket fence test

4 Picket fence test with simulated error Gap 1.5 mm instead of 1 mm mm offset

5 Dose rate and gantry speed control Ratio of RapidArc to open field (%) x (mm)

6 Leaf speed control Ratio of RapidArc to open field (%) x (mm)

7 End-to-end test: Prostate - coronal y (mm) x (mm) 4.9% of pixels have γ > 1 (3%/3 mm)

8 End-to-end test: Prostate - coronal x-profile at y = 0.0 mm y-profile at x = 0.0 mm Film TPS Dose (cgy) Dose (cgy) x (mm) y (mm)

9 Interrupted delivery y (mm) Interrupted Normal x (mm)

10 Treatment planning system Treatment planning system may have additional commissioning requirements

11 The picket fence test during gantry rotation can detect gap and offset errors as small as 20% 20% 20% 20% 20% 0.1 mm 0.5 mm 1 mm 5 mm 1 cm 10

12 The picket fence test during gantry rotation can detect gap and offset errors as small as (2) 0.5 mm C. C. Ling, P. Zhang, Y. Archambault, J. Bocanek, G. Tang, and T. LoSasso, Commissioning and quality assurance of RapidArc delivery system, Int. J. Radiat. Oncol. Biol. Phys. 72, (2008)

13 IMAT QA Most IMRT QA devices measure the fluence from each beam angle for fixed-field IMRT plans. The dynamic nature of VMAT delivery, however, make the fluence measurement undesirable. A composite dose measurement represent a better fit for the purposes of VMAT plan QA.

14 VMAT QA Techniques 1. Film and ion chamber. 2. 2D diode array Mapcheck in MapPhan phantom 3. 2D ion chamber array MatriXX in MULTICube phantom 4. Other 2D/3D diode system Delta4 & ArcCheck 5. Dose reconstruction DosimetryCheck and IBA Compass

15 Film QA Absolute dose measurement Film Coronal Sagittal

16 2D Diode Array A MapCheck device inserted into a MapPhan solid water phantom

17 2D ion Chamber Array.07 cc air-vented ionization chambers Parallel read-out w/o dead time Sampling time: 20 msec 1020 detectors; 24.4 cm x 24.4 cm

18 MapCheck with dose rate correction relative dose response Mapcheck diode MatriXX ion chamber dose rate (MU/minute) The variation of dose response with the dose rate can reach up to 2.5% for MapCheck diode.

19 MapCheck with dose rate correction Dose calibration was performed at 224 MU/Min Gamma passing rate increased to 98.8%

20 Angular dose response of MapCheck diode detector array & phantom Couch Percent Error (%) phantom setup Gantry Angle A variation of the dose response of >20% can be found when the incidence beam angle is parallel to the detector plane. Each diode in MapCheck may have different angular dose response curve.

21 Angular variation of Matrixx dose response detector array & phantom Couch percent error (%) phantom setup Gantry Angle Up to 8% dose variation can be found when the photon beam is parallel to the detector plane

22 Angular response correction for MatriXX Before correction: passing rate 72.7% After correction: passing rate 98.1%

23 Gantry Angle Sensor Sensor is Fixed on the Gantry Inclinometer Detects Gantry Angle OmniPro IMRT Tags Measurement with Angle Correction is Applied

24 Arc Check Sun Nuclear 1386 diode detectors arranged in cylindrical geometry Measures entrance and exit dose Result is a composite dose for entire delivery

25 ArcCheck QA result (H&N) Gamma analysis passing rate is 95.2% for this case.

26 Scandidos Delta 4 A cylinder-shaped plastic phantom with 2 imbedded orthogonal crossing detector planes diode detectors Dose is recorded in 2 planes and a 3D dose is reconstructed for comparison with the QA plan.

27 Delta 4 3D Analysis From the 2D measurments, a 3D dose is reconstructed. User can scroll through slice-byslice. DVH analysis can also be performed. Dose can also be evaluated on a per beam basis and even a per control point basis. Courtesy of Scandidos

28 Gamma Comparison Display (TPS vs. COMPASS)

29 Dosimetry Check Dosimetry Check is a software package available through CIVCO and developed by Dean Renner. Fluences are recorded using the EPID during IMRT/IMAT beam delivery. The dose in patient is then determined as the measured fluence times a Dose Spread Function summed over the irradiated volume. Allows overlay of predicted and measured doses.

30 Reconstructed dose: green from plan, magenta from Dosimetry Check plan courtesy Art Pinkerton, Mississippi. Courtesy W.D. Renner

31 Summary There are a number of viable QA systems for VMAT patient specific QA. It is critical to take the time to characterize the system and understand its limitations. The implementation of a VMAT program may necessitate the purchase of additional QA tools.

32 The variation in angular response of a 2D ionization chamber array is typically 20% 1. Negligible 20% 20% 20% 20% 2. < 2% 3. 2% to 4% 4. 2% to 8% 5. > 8% 10

33 The variation in angular response of a 2D ionization chamber array is typically (4) 2% to 8% A. Van Esch, P. Zhang, C. Clermont C, M. Devillers, M. Iori, and D. P. Huyskens, On-line quality assurance of rotational radiotherapy treatment delivery by means of a 2D ion chamber array and the Octavius phantom, Med. Phys. 34, (2007) J. Bocanek, I. Gomola, T. Depuydt, and F. Van den Heuvel, The feasibility of a 2D ion chamber array and the MultiCube phantom for quality assurance of RapidArc, Radiother. Oncol. 88 (Suppl. 2) S446 (2008)

34 Starting an IMAT program Form an implementation team Develop an implementation plan Establish a timeline Develop written procedures Evaluate training needs Determine case selection guidelines

35 Case selection Simple targets < 12 cm diameter Spherical or cylindrical no bifurcations Start with this... not this

36 Initial cohort standard plans For initial cohort of cases, develop standard plans Use as reference for comparison with IMAT plans Available as contingency treatment plan