DVH-based analysis of pre-treatment verification for VMAT

delivery

Amy Comrie, Andiappa Sankar, Gillian Cooke, Paul Drewell

Edinburgh Cancer Centre

RapidArc QA

• Performed with ArcCHECK phantom & PTW pinpoint chamber for central axis dose measurement

• Gamma passing rates used to compare 2 dose distributions

• 3%/3mm and 2%/2mm Dose Difference (DD) and Distance to agreement (DTA) criterion used for relative and absolute 2D gamma analysis

• Provides no information about size/location of dose errors

Sun Nuclear 3DVH v2.1• Compares two dose matrices using a Planned Dose

Perturbation (PDP) algorithm• Perturbs the planned patient dose matrix to account for

discrepancies between planned and measured dose• Generates 3D local (per structure) and global (per

patient) gamma passing rates, DVH-curves and dose statistics

Software input includes:• DICOM RT Plan, Dose, Structure set & planning CT data

set• Comparison dose file (.acml from ArcCHECK)

3DVH Software output

3DVH Analysis

• 15 RapidArc patients (11 H&N and 4 Prostate)

• 2%/2mm and 3%/3mm gamma analysis, 10% threshold (local and global)

• Comparison of ArcCHECK and 3DVH gamma analyses

• Comparison of 3DVH and Eclipse DVH curves

• Comparison of Eclipse and 3DVH volumes

• Dmean, Dmax, D90% & D95% for PTVs

Results (1)

ArcCHECK and 3DVH Gamma Analyses (1)

ArcCHECK and 3DVH Gamma Analyses (2)

3DVH and Eclipse DVH differences

3DVH and Eclipse volume differences

Differences in Dmax

Potential Errors/Issues

• ArcCHECK setup and temperature dependence• Differences between Eclipse and 3DVH

volumes• Possible differences between AAA and Planned

Dose Perturbation algorithms• Comparison of measured dose to a phantom

with planned dose to a patient

How effective is 3DVH?

• Successfully generated DVH data using 3DVH and compared to Eclipse DVH curves

• All patients passed our ArcCHECK pre-treatment QA• 13 out of 15 patients passed 3DVH analysis, no

obvious reason for 2 failures• No relationships between volume or Dmax differences

for individual structures and gamma passing rates were found

• Future work includes analysing overall benefits of using 3DVH and the clinical significance of errors (PTV coverage, OAR overdose etc.)

References

• Carrasco, P. et al. (2012) 3D DVH-based metric analysis versus per-beam planar analysis in IMRT pretreatment verification, Medical Physics, 39(8) pp.5040-5049

• Zhen, H., Nelms, B.E. & Tome, W.A (2011) Moving from gamma passing rate to patient DVH-based QA metrics in pretreatment dose QA, Medical Physics, 38 (10) pp.5477-5489

• Nelms, B.E., Zhen, H. & Tome, W.A. (2011) Per-beam, planar IMRT QA passing rates do not clinically predict clinically relevant patient dose errors, Medical Physics, 38(2) pp.1037-1044