Introduction of RapidArc TM : an example of commissioning and implementing a QA programme for a new technology

Transcription

1 Introduction of RapidArc TM : an example of commissioning and implementing a QA programme for a new technology Philip Mayles Clatterbridge Centre for Oncology, Wirral, UK 1

2 What is RapidArc (or VMAT)? An isocentric treatment in which the dose rate, gantry speed, and MLC leaf positions are all changing Treatment carried out in a single rotation Two rotations may improve distribution Substantially reduced treatment time 2

3 Step One Establish a multidisciplinary team Doctors Physicists Radiation Technologists 3

4 The Team Clinical Oncologist Isabel Syndikus Physicists Helen Mayles, Richard Clements, Julie Kirk, Simon Temple, Stephen Riley Radiation Technologists Ruth Clements, Angela Heaton Their contributions to this talk are gratefully acknowledged 4

5 Tasks for the Team Requirements for the treatment machine to deliver VMAT accurately Quality control procedures Planning system parameters that may need to be known more accurately Phantom measurements to verify achievable accuracy Requirements and methodology for ongoing quality assurance of patient treatment plans Patient setup and verification 5

6 How does it work? MLC leaf positions are linked to the gantry rotation angle Gantry rotation is linked to dose delivered Control points have a cumulative dose value, MLC leaf positions and gantry angle Machine calculates gantry speed and dose rate 6

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9 What can go wrong MLC leaf speed Gantry speed Dose rate control MLC leaf calibration 9

10 Machine Tests Following Ling et al IJROBP

11 Variable Leaf Speed Test 4 dynamic segments (From Right to Left) Field width 30 mm 4.6 mm/s 138 MU/min 9.2 mm/s 277 MU/min 18.4 mm/s 554 MU/min Field width 45 mm 27.6 mm/s 554 MU/min

12 Dose Rate Test 7 segments 111 MU/min for MU/min for MU/min for MU/min for MU/min for MU/min for 15 at 5 /s 600 MU/min for 12.9 at 4.3 /s Equivalent to 0.33, 0.67, 1.0, 1.33, 1.67, 2 and 2.33 MU/ RADR

13 Static Rapid Arc

14 Static Rapid Arc

15 Static Rapid Arc

16 Static Rapid Arc

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18 Comparative Patient Plans Aim to demonstrate that RapidArc produces plans that are better or at least equally good Consider different sites one by one 18

19 Rapid Arc Prostate Simultaneous Boost IMRT

20 Prostate Simultaneous Boost Boost Prostate + Seminal Vesicles Bowel Rectum Femoral Heads Bladder RapidArc IMRT

21 Rapid Arc Prostate and Pelvic nodes IMRT

22 Prostate and Pelvic nodes Femoral Femoral Heads Heads Bowel Bowel Prostate Prostate Prostate + Seminal Prostate Vesicles + Seminal Vesicles Pelvic Pelvic nodes nodes Bladder Bladder Rectum Rectum RapidArc RapidArc IMRT IMRT

23 Individual Patient QA Many current systems just allow one beam to be analysed We need to look at the composite beam in 3D Delta4 has been specially adapted for RapidArc including gantry angle monitoring 23

24 Delta4 3D Diode Phantom

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26 Couch Model

27 Effect of couch correction

28 Effect of couch correction

29 Individual Patient QA Many current systems just allow one beam to be analysed We need to look at the composite beam in 3D Delta4 has been specially adapted for RapidArc including gantry angle monitoring We have also mounted it on a carriage that allows us to observe the effect of breathing 29

30 Delta4 Mounted on a Moving Carriage to Simulate Respiration

31 Individual Patient QA Many current systems just allow one beam to be analysed We need to look at the composite beam in 3D Delta4 has been specially adapted for RapidArc including gantry angle monitoring We have also mounted it on a carriage that allows us to observe the effect of breathing For absolute dose measurements it is useful to have a patient shaped phantom 31

32 Water Phantoms for QA

33 Individual Patient QA Many current systems just allow one beam to be analysed We need to look at the composite beam in 3D Delta4 has been specially adapted for RapidArc including gantry angle monitoring We have also mounted it on a carriage that allows us to observe the effect of breathing For absolute dose measurements it is useful to have a patient shaped phantom It is also important to check reproducibility of delivery 33

34 Repeatability

35 Individual Patient QA Many current systems just allow one beam to be analysed We need to look at the composite beam in 3D Delta4 has been specially adapted for RapidArc including gantry angle monitoring We have also mounted it on a carriage that allows us to observe the effect of breathing For absolute dose measurements it is useful to have a patient shaped phantom It is also important to check reproducibility of delivery For some patients geometric accuracy is a key factor 35

36 Multiple Brain Metastases

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41 Conclusions New techniques need new approaches to QA Assessment of the risks can highlight those areas that need to be assessed A well documented process should be followed with independent review Machine QA should be ongoing The benefits of RapidArc appear to outweigh the potential risks 41