ESTRO 36 Abstract Book

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S414 ESTRO 36
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Purpose or Objective
PBS, recently developed, scans a tumor with very precise
beam of protons that’s accurate within millimeters,
sparing the healthy surrounding tissues. But it is able to
harmful rather than conventional radiotherapy if the beam
is not accurately irradiated as planned. It is very important
to measure beam width and spot center of the proton
pencil beam for the accurate delivery of dose to the target
volume with a good conformity. We have developed the
beam monitoring system using Array of Fiber-Optic
Cerenkov Radiation Sensor (AFCRS), and conducted
feasibility study for proton pencil beam.
Material and Methods
We have developed a fine segmented detector array to
monitor PBS. A prototype beam monitor system using
AFCRS has been developed for real-time display of the
pencil beam status during the PBS mode operation. The x-
y monitoring system with 128 channel readout is mounted
to the snout for the in-situ real time monitoring. Beam
widths and spot centers of various energies are measured.
Two dimensional Gaussian fit is used to analyze the beam
width and the spot center. The ability of this system to
evaluate Lynx system (Scintillator-based sensor with CCD
camera) and EBT3 for PBS was compared.
Results
The measured Gaussian widths using AFCRS changes from
13 to 5 mm for the beam energies from 100 to 226 MeV.
The beam widths of PBS using the AFCRS are well matched
with the data acquired by a Lynx system and EBT 3 film.
In addition, spot centers for 226 Mev PBS beams are also
well matched with RTP system.
Conclusion
The dosimetric performance of the newly developed
system based on AFCRS was comparable to that of the Lynx
system and EBT3 film. Not only measuring the spot profile
but also monitoring dose map by accumulating each spot
measurement will be available.
PO-0781 A characterisation of EBT3 Gafchromic film for
relative and absolute dosimetry
I. Billas1, H. Bouchard2, A. Subiel1, I. Silvestre1, S. Duane 1
1 National Physical Laboratory, Radiation Dosimetry,
Middlesex, United Kingdom
2 Université de Montréal, Département de physique,
Montréal, Canada
Purpose or Objective
The aim of this work is to investigate the variation in dose
response of Gafchromic EBT-3 film within each film and
across films from different boxes and lots. In this way the
uncertainty of relative and absolute dosimetry using EBT-
3 film is quantified and its potential for use in small field
and MRI-guided radiotherapy is better understood.
Material and Methods
Sheets of Gafchromic EBT-3 film were uniformly irradiated
in a cobalt-60 beam in increments of 1 Gy up to a
cumulative dose of 10 Gy. Films were scanned repeatedly
before the first irradiation and after each step. Software
for image processing and analysis was implemented in
MATLAB, allowing determination of the correction for
scanner inhomogeneity and calibration of film optical
density (OD) response in terms of absorbed dose to water.
Regions of interest (ROIs) of various sizes were used to
sample image data, quantifying the uncertainty associated
with variations within each film, from film to film within
the same lot, and from lot to lot. 35 sheets of film were
used, taken from 7 boxes across 3 lots. Three channels of
optical density (OD) data were analysed statistically, both
directly as OD and also in the ratios red/blue and
green/blue. Net values were obtained by subtracting pre-
irradiation values, and a normalisation correction factor,
based on large dose saturation values, was applied.
Results
The figure shows the net ratio of OD, green/blue, before
and after applying the normalisation correction, as a
function of dose, for ROIs which are 10 x 10 mm2. The
table lists the relative standard deviation of absorbed dose
measurements made using EBT-3 in the present work.
Conclusion
By combining the subtraction of pre-irradiation values,
with a normalisation correction based on large dose
saturation values, it should be possible to reduce the
contribution to measurement uncertainty arising from
intrinsic variations in the characteristics of EBT-3 film to
0.7 % ( k=1) for doses in the range of up to 5 Gy.
PO-0782 New liquid ionization chamber detector of
high resolution for treatment verification in
Radiotherapy
L. Brualla-Gonzalez1, A. Vázquez-Luque2, M. Zapata 3,4,
D.M. González-Castaño3,5, V. Luna-Vega 4, J. Guiu-Souto 4,
D. Granero1, A. Vicedo1, M.T. García-Hernández1, J.
Roselló1,6, M. Pombar3,4, F. Gómez3,7, J. Pardo-Montero3,4
1Hospital General Universitario de Valencia, Servicio de
Radiofísica ERESA, Valencia, Spain
2Detection And Radiation Technologies SL, Development,
Santiago de Compostela, Spain
3Instituto de Investigación Sanitaria IDIS, Grupo de Imaxe
Molecular, Santiago de Compostela, Spain
4Complexo Hospitalario Universitario de Santiago de
Compostela, Servizo de Radiofísica e Protección
Radiolóxica, Santiago de Compostela, Spain
5Universidade de Santiago de Compostela, Laboratorio
de Física de Partículas RIAIDT, Santiago de Compostela,
Spain
6Universidad de Valencia, Departamento de Fisiología de
la Facultad de Medicina, Valencia, Spain
7Universidade de Santiago de Compostela, Departamento
de Física de Partículas, Santiago de Compostela, Spain
Purpose or Objective
In this work we present a new liquid ionization chamber
array prototype for patient treatment verification. The
objective of its design is to offer a high spatial resolution
with 100% fill factor.
Material and Methods
The prototype has 2041 liquid ionization chambers of
2.5x2.5 mm2 effective area and 0.5 mm thickness. The
detection elements are arranged in a central square grid
of 43x43, covering an area of 107.5x107.5 mm2. The
central inline and crossline are extended to 227 mm and
the diagonals to 321 mm. The active medium is liquid
isooctane.
We have studied short- and medium-term stability, dose
rate dependence, depth and field size dependence,
anisotropy and leaf positioning detectability.
We have measured output factors, tongue-and-groove,
garden fence, small field profiles and irregular fields.
Finally we have used it for the verification of patient
treatments.