ESTRO 36 Abstract Book

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S502 ESTRO 36
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Conclusion
These preliminary data show that fractal and lacunarity
analysis may be able to characterise areas of restricted
diffusion and non-restrictive diffusion on ADC
images. Restrictive diffusion often indicates areas of
aggressive prostate tumour. This method could be used in
future studies to investigate other MR sequence images
where the visual difference between prostate tumour and
normal tissue is not so obvious to the naked eye, or where
simple analysis of multiparametric data fails to adequately
characterise tumour biology.
Poster: Physics track: Implementation of new
technology, techniques, clinical protocols or trials
(including QA &audit)
PO-0907 Remote auditing of IMRT/VMAT deliveries
N. Miri 1, K. Legge2 , J. Lehmann3, P. Vial4, B. Zwan5, P.
Greer6
1 University of Newcastle, School of Mathematical and
Physical Sciences, Newcastle- NSW, Australia
2 University of Newcastle, School of Mathematical and
Physical Sciences, Newcastle, Australia
3 Calvary Mater Newcastle Hospital, Radiation and
Oncology, Newcastle, Australia
4 Liverpool and Macarthur Cancer Therapy Centres,
Department of Medical Physics, Sydney, Australia
5 Gosford Hospital, Central Coast Cancer Centre,
Gosford, Australia
6 Calvary Mater Newcastle Hospital, Radiation and
Oncology departement, Newcastle, Australia
Purpose or Objective
Purpose: To perform a novel study on remote auditing of
dose deliveries of VMAT/IMRT clinical trials of different
radiotherapy centres. The assessment is undertaken using
EPID images from the centres and a local ‘signal to dose’
conversion model.
Material and Methods
Methods: The assessment included IMRT deliveries from 12
centres and VMAT deliveries from 6 centres. The centres
downloaded benchmarking CT data sets and instructions
to produce IMRT/VMAT trial plans, a head and neck (H&N)
and post-prostatectomy (P-P) plan. Two virtual phantom
data sets were provided for a flat and a cylindrical
phantom. Trial plans were transferred to the phantoms;
individual field/arcs at gantry zero on the flat phantom
and the trial plan at actual gantry angles to the cylindrical
phantom. EPID images acquired from a calibration plan
were used to align and calibrate the EPID systems and
model/correct EPID-linac sag. Integrated images were
acquired for IMRT fields and cine images for VMAT arcs
each cine image encompassing approximately 5 degrees.
For 2D and 3D analysis, the images were converted to dose
inside respectively the virtual flat and cylindrical
phantom. The dose conversion was performed using an
established model. To assess the delivered doses, the
modelled dose was compared with corresponding TPS dose
using the gamma function with all doses greater than 10%
of the global maximum dose assessed.
Results
At 3%/3mm, 2D analysis of the H&N plan resulted in 99.6%
(SD: 0.1) and 99.1% (SD: 0.1) mean pass rates for
respectively IMRT and VMAT deliveries. Similarly, the P-P
plan analysis resulted in 99.7% (SD: 0.2) and 99.6% (SD:
0.3) mean pass rates for corresponding deliveries over the
centres. 3D analysis, on the other hand, resulted in slightly
lower pass rates. H&N deliveries resulted in 98.3% (SD:
0.2) and 96.4% (SD: 2.6) mean pass rates. The P-P plan
assessment resulted in 98.3% (SD: 1.5) and 97.2% (SD: 1.3)
mean pass rates. Using a more stringent criteria, 3%/2mm,
the H&N analysis resulted in 92.2% (SD:1.9) and 93.3% (5.4)
mean pass rates and the P-P plan resulted in 94.0%
(SD:4.3) and 95.6% (SD: 1.8) mean pass rates for
respectively IMRT and VMAT deliveries. For VMAT
deliveries, slightly higher standard deviation was observed
than IMRT.
Figure 1- Planar dose assessment of the centres for head
and neck and post-prostatectomy plans: a) IMRT delivery,
b) VMAT delivery
Figure 2- 3D dose assessment of the centres for head and
neck and post-prostatectomy plans and: a) IMRT delivery,
b) VMAT delivery
Conclusion
All linacs were equipped with EPIDs so a consistent
detection system was used by the centres. The method
was significantly less expensive and faster than
conventional audits due to its remote nature and use of
virtual phantoms. All measured data were analysable with
relatively high pass rates. Interactive communications
with centres was often necessary to ensure quality data
were provided.
PO-0908 Application of Failure Mode and Effects
Analysis to linac quality controls: advantages and limits
F. Bonfantini1, T. Giandini1, S. Meroni1, C. Stucchi1, M.
Carrara1, V. Mongioj1, I. Veronese 2, E. Pignoli1
1Fondazione IRCCS Istituto Nazionale dei Tumori, Medical
Physics, Milan, Italy
2Università degli studi, Physics, Milan, Italy
Purpose or Objective
The increased complexity of the modern linac-based
radiotherapy requires more thorough quality assurance
programs to reduce the risk of errors and ensure patient
safety. However, these demands are cumbersome and the
efforts should be optimized in order to take maximum
advantage of the available resources. In this context,
prospective methods for risk analysis, such as Failure Mode
and Effects Analysis (FMEA), can be a useful tool. Aim of
this work was to evaluate advantages and limits of the
application of FMEA for the optimization of linac quality
controls (QCs).
Material and Methods
Each parameter tested by the QC was considered as a
potential failure mode (FM) and a Risk Priority Number