Patient specific QC in Aarhus

1
Patient specific QC in Aarhus

• Lone Hoffmann
• Ulrik Vindelev Elstrøm, Mai-Britt Kyed Jørgensen

2
VMAT introduction

• Introduced in May 2009
• First patient June the 17th, 2009
• Treated approx. 800 patients
• Primarily pelvic cancers
• Prostate, cervix, bladder, anal, rectum,..
• Other types
• Brain, sarcomas, abdominal

3
Patient specific QA

• Perform Delta4 verification for all patients
• Normalization to daily output
• Gamma(3,3) gt 95
• Most patients G(3,3) gt 97

4
Test/learning plans

• 10 prostate plans (15MV)were created with
• 250MU, 500MU, 750Mu, 1000MU, 2000MU
• In 1 or 2 arcs
• 10 HN plans (6MV) were created with
• 250MU, 500MU, 750Mu, 1000MU, 2000MU
• In 1 or 2 arcs
• 2 Gy/fx

5
G(3,3) vs. MUs

• G(3,3) decreases as a function of MUs
• Planning criteria MU lt 400 for 1/2 arcs

6
G(3,3) vs. accelerator

• Differences between accelerators

7
Test plans used for QA

• 6 of the test plans are use for QA 4 times a year
  each acc.
• Plans with high G(3,3) are very stable (within
  2-4)

Low/moderate modulation
High modulation
8
Test plans used for QA

• Some accelerators are more stable than others
• Acc1 performs bad in autumn 2011 no problems
  with mashine QC

9
Acc QC vs. Patient spec QC

• Problems with acc QC on acc 5 (spring 2011)
• Not seen for patient specific QC

Low dose rate
DRMLC test
10
Real patient plans

• Reproducibility for each acc
• Difference between acc not seen with acc QC

acc3
11
True beam

• 5 patients treated at Clinac and True beam
• G(3,3) does not depend on Clinac/True beam?
• MeanG(Clinac)98.4
• MeanG(TrueBeam)99.0

12
Portal dosimetry

• Use EPID/MVD for patient specific QC
• Fast measurement
• Ideal for routine measurements

13
Delta4 vs. PDI

• Perform Delta4 and PDI measurement consecutively
  at same accelerator
• Preliminary results, Oct-Dec 2011
• 68 plans (1,2, ..6 arcs)
• 127 single arcs
• Single arcs
• G(3,3)D4
• 1.7 higher than G(3,3)PDI
• Plans
• G(3,3)D4
• 1.0 higher than G(3,3)PDI
• Pass criteria
• G(3,3)D4 95 G(3,3)PDI 94

14
Work in Progress

• Measurement of D4 and PDI for same plan at
  different accelerators
• Analysis of data (approx 100 plans and 10 new
  plans pr week)
• Workflow today
• Daily PDI used for accept/reject
• Weekly D4 used for check
• Future
• Only PDI
• New/additional machine QC program

15
Machine QC program

• MV imager
• Test of clinical dose rates
• Test of reverse gantry direction
• Test of gantry position
• Delta4
• Still of measurement of 6 test plans 4xyear each
  accelerator