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contribution of microscopic lung parenchyma (below CT
resolution).
PO-0788 First assessment of Delivery Analysis tool for
pre-treatment verification on the new Radixact system
A. Girardi
1
, T. Gevaert
1
, C. Jaudet
1
, M. Boussaer
1
, M.
Burghelea
2
, J. Dhont
1
, T. Reynders
1
, K. Tournel
1
, M. De
Ridder
1
1
Universitair Ziekenhuis Brussel, Department of
Radiotherapy- Universitair Ziekenhuis Brussel- Vrije
Universiteit Brussel- Brussels- Belgium, Brussels, Belgium
2
Brainlab AG, BRAINLAB AG Feldkirchen Germany,
Brussels, Belgium
Purpose or Objective
To evaluate the accuracy of the Delivery Analysis (DA) tool
for patient-specific pre-treatment verification and the
sensitivity to detect discrepancies in dose delivery in
comparison with widespread detectors.
Material and Methods
The Radixact machine is equipped with the DA device for
pre-treatment Quality Assurance (QA) and interfraction
verification. This tool is designed to assess the consistency
of the delivered treatment through the detector data and
to show anatomical changes of the patient. The latter
representing a powerful tool to be coupled with Adaptive
Radiotherapy. The idea is to use the detector: a) to
measure the Multileaf Collimator (MLC) leaf open time, b)
to compare the planned sinogram to the delivered one and
c) for dose reconstruction purposes. In this study, we
performed pre-treatment verification on the very first
twenty heterogeneous patients treated worldwide (target
volumes ranging between 98 to 4179 cc) using the DA, the
Sun Nuclear MapCheck2 (MC2) and the ScandiDos Delta4
(D4).The Gamma Index was used to show the agreement
between dose planning calculations and measurements.
To compare the three methods, criteria were set to 2% and
3% in local dose and to 2mm and 3mm in distance,
respectively, excluding doses lower than 20% of the
maximum doses. The performances of the systems were
analysed with a single factor ANOVA test, with a
significance level of α=0.05. A possible dependence of the
results from the target volume was furthermore explored
with a simple linear regression analysis.
Results
The ANOVA test showed no statistically significance
differences between the performances of the three
systems, both for the 2%/2 mm and the 3%/3mm criteria
(p-values equal to 0.351 and 0.660 respectively). The
linear regression indicated a variation of performance as
a function of target volume for the MC2 (R
2
2%/2mm
=0.819
and R
2
3%/3mm
=0.979) and the D4 detectors (R
2
2%/2mm
=0.991
and R
2
3%/3mm
=0.990), which is not highlighted for the DA
system (R
2
2%/2mm
=0.283 and R
2
3%/3mm
=0.290). This
difference could be related to the missing data due to the
larger dimension of the dose map with respect to the
detection area of the MC2 and D4 systems.
Conclusion
This study showed that the performances of the Delivery
Analysis tool for the new Radixact machine is not different
from those of two other widespread detectors for pre-
treatment verification. Moreover, the linear regression
test showed that the performances of the system are not
correlated with the target volume, as is the case for two
other detectors used in the study, proving its sensitivity as
a patient specific QA tool.
PO-0789 Demystifying failed VMAT PSQA
measurements with ArcCHECK
P. Kinsella
1
, L. Leon-Vintro
2
, B. McClean
3
1
St Luke's Radiation Oncology Center, Physics, Dublin,
Ireland
2
University College Dublin, School of Physics, Dublin,
Ireland
3
St Luke's Radiation Oncology Network, Physics, Dublin,
Ireland
Purpose or Objective
A means of reducing PSQA measurements for VMAT is
currently a popular topic of discussion due to the resource
burden it generates and the increased use of VMAT. The
reluctance to reduce or replace PSQA may be partly due
to the difficulty in identifying the cause/s of plan failures.
Plans may fail due to a large number of potential factors
caused by the TPS, linac or measurement device. The goal
of this study was to uncover the reason/s why a selection
of VMAT plans have failed.
Material and Methods
Five ‘bad’ plans yielding low (failing) gamma pass-rates
and high average gamma-values were s elected for
analysis. Two ‘good’ plans yielding high gamma pass-rates
and low average gamma values were also used for
comparison. The plans were measured with SNC ArcCHECK
(1220 Model) cylindrical detector diode array and analysed
with gamma analysis in SNC Patient software. The
institutional tolerance was ≥95% of the points must pass a
gamma analysis with 3% and 2mm gamma criteria, with a