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S497
ESTRO 36 2017
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Purpose or Objective
MR has the ability to assess numerous physiological and
biochemical tumour characteristics. Fractal analysis may
provide a better insight into the biology and behaviour of
prostate tumour than simplistic comparisons of
multiparametric data. In this pilot study, we aim to
determine whether fractal and lacunarity analysis can
characterize the properties of radio-recurrent prostate
cancer, using Apparent Diffusion Coefficient (ADC) MR
Images.
Material and Methods
Retrospective analysis of eight patients with recurrent
prostate cancer after previous radical radiotherapy (mean
age: 71.25 years), underwent MRI examination for re-
staging prior to consideration of salvage therapy. ADC
images of the prostate were manually segmented from
surrounding tissue and a region of interest (ROI) drawn to
distinguish between restrictive diffusion and non-
restrictive tissue (figure 1b). Low, medium and high ADC
value maps were generated by intensity thresholding the
respective restrictive and non-restrictive ROIs. These
were processed and converted to 8-bit black and white
images (figure 1c, low intensity in restricted diffusion) for
application to in-house textural analysis software (image
1d) to estimate (a) fractal dimension (b) fractal
abundance and (c) lacunarity
Curve1
Figure 1:
(a) an ADC image of the prostate gland (b) an
ADC image showing areas of restricted diffusion (red) and
non-restricted diffusion (blue) (c) shows a binary image
used for fractal and lacunarity analysis (d) lacunarity
curves from restricted areas (red) and non-restricted
areas
(blue)
Results
The average fractal characteristics are summarised in
table 1 with the fractal dimension between areas of
restricted diffusion and non-restrictive diffusion of the
low and medium intensity images being of significant
difference (p=0.0014 and 0.0023 respectively). The
fractal abundance of the medium intensity image between
the restricted diffusion and non-restrictive diffusion was
also significant (p=0.0012).
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. Legge
2
, J. Lehmann
3
, P. Vial
4
, B. Zwan
5
, P.
Greer
6
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