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Title: Free PowerPoint poster templates


1
Computed Verification of light and Radiation
field size Superimposition on Cobalt-60 Yousif
M. Yousif Abdullah, Mohamed Elfadil M.
Gar-elnabi, Khalid H. Eltom, Mohamed Ahamed A.
Omer  Radiotherapy Department, College of Medical
Radiologic Science, Sudan University of Science
and Technology, Sudan. Crossing Elguish St. and
Elshahid St. P.O. Box.1908, Fax24983785215,email
yousifmohamed_at_sustech.edu
About this template
Methods and Materials
Results
The verification of light and radiation field is
essential for radiotherapy process if the light
field does not match the radiation field that
resulting from central axis dose measurements and
treatment planning account to about 5 of an
optimal situation which the uncertainties so an
effective quality assurance program should
include port film reviews, and tests of machines
for beam alignment. This study was performed in
Radiation and Isotopes Center of Khartoum (RICK)
in period of April 2009 to August 2009. The main
objective of this study was to verify the
superimposition of light and radiation field
automatically by using image processing
technique. For radiotherapy machines (Co-60) each
film scanned using digitizer scanner then treat
by using image processing program IDL, where the
congruence of the light and radiation field
should be determined. The scanned image will be
saved in a TIFF file format to preserve the
quality of the image. The data analyzed include
upper, lower, right and left borders of the light
and radiation field in telecobalt megavoltage
films. The result showed that the mean light
field size was (10.0 X 10.1cm), Medical physicist
score was (10.2 0.11608 X 10.2 0.099861 cm)
and the field size that calculate by computerized
score using IDL program was (9.9 0.36049 X 9.9
0.1123cm), the result also showed that the
Computerized score is more accurate in
determining of borders and Penumbra than medical
physicist score. The computerized score
technique, even in relatively simple images,
could be disturbed by noise, creating some small
regions that required additional processing. On
the contrary, the manual method ignored those
details to focus only on the expected boundaries
which were determinate incorrect
This study deal with radiation and light field
size that was scored objectively by computer
program and subjectively by medical physicist.
Chi-square test was been performed for all score
variations in this study. P-value was calculated
to show if there is any significant impact of
each light and radiation field size variation
.
This is an experimental study conducted to
determine the superimposition of the light and
radiation field objectively using computer
techniques in respect to certain parameters.
Materials Cobalt-60 machine The data was
collected from megavoltage machines (cobalt-60
and linear acceralator). Cobalt-60 unit is known
as THERATRON ELITE 100. They are teletherapy
units, classified as class 1, type B. The sources
are quantity of metallic radioisotope, cobalt-60,
sealed inside 2 cm long. Typically, the sources
are about 2.0 cm in diameter. The maximum
absorbed dose rate in air for the maximum
cross-section of the radiation beam at 1 meter
from the radiation source is approximately 250
cGy/min Figure 4. Methods For
radiotherapy machines (Co-60) each film scanned
using digitizer scanner then treat by using image
processing program IDL, where the congruence of
the light and radiation field will be determined.
The scanned image will be saved in a TIFF file
format to preserve the quality of the image. The
data analyzed include upper, lower, right and
left borders of the light and radiation field in
telecobalt megavoltage films. The researcher used
to score the verification film subjectively by
placing a ready pack direct exposure film on the
table on the source to axis distance (SAD) Figure
5. With the collimator angle set at 0
degrees, 10 x10 cm square light fields was
obtained and mark the edges with a radiopaque
object or a ballpoint pen by drawing lines on the
film jacket with sufficient pressure to scratch
the emulsion. Then the film was exposed for 1-2
minutes to obtain an optical density in the
linear range of its sensitmetric curve, usually
around 1. Two more exposures at the collimator
angles of 90 degrees were made using fresh area
of the same film or another film. The film was
processed in an automatic rapid processor. With
millimeter graph paper attached to the patient
treatment table was raised to the nominal
isocenter distance the gantry was orientated to
point the collimator axis of rotation vertically
downwards. The position of the collimator axis of
rotation was indicated on this graph paper. The
projected image of the cross-hair should be
coincident with the collimator axis of rotation
and should not deviate more than 1 mm from this
point as the collimator is rotated through its
full range of motion. The projected images of the
jaws should open and close symmetrically about
this point Figure 6. The symmetry of the
collimator jaw images about this point should be
better than 1 mm at all cardinal angles of the
collimator. The congruence of the light and
radiation field can now be verified. A ready pack
of radiographic film was placed perpendicularly
to the collimator axis of rotation. The edges of
the light field are marked with radio-opaque
objects or by pricking holes with a pin through
the ready pack film at the corners of the light
field. The film was positioned near zmax by
placing plastic on top of it and is irradiated to
yield an OD of between 1 and 2 mm Figure
6. The congruence of the light and
radiation field was verified in the center, upper
and the lower of the field, and then the reading
was obtained by the IDL. The researcher
calculated the data analyzed include upper,
lower, right and left borders of the light and
radiation field.
Table (2) shows the variables (light, radiation)
field size the mean standard deviation to
them.
Variables Mean SD
Light field size (10.0 0.1137 cm) X(10.10.9973cm)
Radiation field size (Manual score) (10.2 0.11608cm)X (10.2 0.099861 cm)
Radiation Field Size (Automatic Score) (10.10.36649 cm)X(10.1 0.24599 cm)
Trimmer bars (SDD-cm) Minimum Field size (cm) Maximum Field size (cm)
45 5.0 4.0 43.0 43.0
55 4.0 4.0 42.0 42.0
Figure 4. Shows EQUINOX 100 telecobalt machine
Introduction
The verification of light and radiation field is
crucial process for radiotherapy process. The
portal verification of the positioning of these
radiation and light fields is carried out by
comparing the location of the treated portal
image of radiation taken during delivery with the
reference simulation, which is an image taken on
a simulator or a digitally reconstructed
radiograph (DRR). Developing an efficient method
for an automated verification of the treatment
portal localization is crucial to the quality
assurance of conformal radiotherapy. If
localization accuracy is improved, it is possible
to envision applying higher dosage to the tumor
with exclusion excess to normal tissues . The
geometrical field size is the projection, on the
plane perpendicular to the beam axis, of the
distal end of the collimator as seen from the
front size All the energy supplied to the
induction field is returned to the antenna by the
collapsing E and H fields. No energy from the
induction field is radiated from the antenna.
Figure 1. An image as it may be applied to a
picture such as a photograph, a painting or a
sketch which has a real physical existence. But
it may be also being applied to an idea or
concept which has a mental rather than physical
existence. Image analysis is simply the
extraction of information from pictures. Sight is
(arguably) the most important sense scientists
have. It is said that a picture is worth a
thousand words' (a view shared by Charlie Brown's
little sister). Some image analysis is more
easily done by the human eye, but for other tasks
a computer is better. To study atrophic rhinitis,
a disease of the upper respiratory tract in pigs,
snouts of dead pigs were cut in half the exposed
cross-sections were then inked and printed on
paper. Figure 2-1a shows a print from a
disease-free pig. It is important in any
practical application of image analysis to
consider whether, by collecting data in a
different way, image interpretation could be made
simpler. For example, variations in illumination
can sometimes be dealt with by collecting two
images, one with the specimen present and one of
the background alone, then forming a pixel by
pixel ratio.
Figure (4-2) shows (a)Co-60 radiograph (b)
Computerized Radiograph plotting profile
Conclusion
The computerized method results were attractive
considering that only one image was deemed
unacceptable. From the start, this image was
considered the ultimate' difficulty even for the
human eye. Both in terms of segmentation results
and computational times, the computerized method
was much stronger in the context of an automated
process to detect radiation fields. IDL program
used to objectively score the alignment of the
photon field that was unable to detect by naked
eye special in megavoltage machines. The
computerized technique depended on global
information to segment the image. It was
efficient when the regions of interest were
clearly defined (i.e., field edges and center
regions) because an effective computerized score
could separate the different regions in the
image. However, when density variations in those
regions were more important than the variations
between regions, that technique could not
correctly identify a threshold. In contrast, the
computerized method relied on local gradient
information to determine where the next position
of the curve was. Therefore, as demonstrated when
using the initial contour close to the
boundaries, it was not perturbed by the density
variations inside the treated area. However, the
computerized method was more sensitive to those
internal density variations when the initial
front consisted of scattered points more of the
inside of the treated area was used as local data
to determine the next movement of the curve,
re-introducing some of the global information
problem encountered by the thresholding
technique. So conclusion of this research that
the congruence of the light and radiation field
that the light field edge should correspond to
the radiation field edge within 2 mm. The
alignment of the photon field is a complex
procedure that should only be performed by
medical physicist which is difficult to detect by
naked eye especially in megavoltage film which
can easily detect by using image processing
programs to analysis irradiated film.
Figure 5. Shows Researcher is placing a ready
pack direct exposure film on the table on the
source to axis distance (SAD)
A B
References
  • Adelson, E.H., Bergen, J.R. 1991. "The plenoptic
    function and the elements of early vision", In
    Computation Models of Visual Processing, M. Landy
    and J.A. Movshon, eds., MIT Press, Cambridge,
    1991, pp. 3-20.
  • Arvo, J., 1994, The Irradiance Jacobian for
    Partially Occluded Polyhedral Sources, Proc. ACM
    SIGGRAPH, ACM Press, pp. 335-342.
  • Farr, R., Allisy-Roberts, P., 1997, Physics for
    medical imaging, W.B. Saunders, London.
  • Leszczynski KW, Shalev S, Cosby NS., 1992,
    enhancement of radiotherapy verification images
    by an automated edge detection technique. Journal
    of Applied Medical Physics, Volume 19, p.p.
    611-621.
  • Picker International, 1997, digitally composited
    radiographs (DCRs) AcQsim TM CT simulation and
    radiation treatment package product data, Picker,
    USA. Presscribing, recording and reporting photon
    beam therapy, Report 52. ICRU, Maryland.
  • Thayalan K., 2001, Basic Radiological Physics,
    Jaypee Brothers Medical Publisher Ltd, New Delhi.
  • Webb, R., 1987, Principles of Radiological
    Physics in Practice, Oxford University Press,
    Oxford.

Figure 5. Shows Researcher marked the edges of
field with a radiopaque object or a ballpoint pen
by drawing on film jacket.
Description of image processing Algorithm
IDL (the Interactive Data Language) is a complete
computing environment for the interactive
analysis and visualization of data. IDL
integrates a powerful, array-oriented language
with numerous mathematical analysis and graphical
display techniques. The researcher used the IDL
signal processing to perform basic image
processing techniques such as simple blurs, the
Fourier transform, interpreting FFT results,
displaying FFT results, FFT algorithm, the Hibert
transform, wavelet transform, Convolution,
Correlation and Covariance, digital filtering,
Finite Impulse Response (FIR), FIR filter
implementation, Infinite Impulse Response filter,
edge detection, transfer functions and
morphological operators (Fig. 3). the Sobel edge
detection filter can be implemented by performing
the following operations 1) Apply a Gaussian
blur 2) Compute the partial derivatives at each
Pixel 3) Compute the Magnitude and direction of
the line (tan-1) at each point 4) Sample the
neighbors in the direction of the line and
perform nonmaxima-suppression (Fig. 4). .
Acknowledgement
The authors would like to thank everyone who help
in the way or other to make this work appear to
light.
Figure3-4. Shows Cobalt-60 radiograph
Figure 3. Shows Visual code marker
Figure 4. Shows Edge Detection Sobel Filter
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