1. Monte Carlo comparison study of the radiation
absorption of scintillators for use in Diagnostic
Radiology and Nuclear Medicine Applications.
Authors:
T. J. Sevvosa, A. A. Fotopoulosa, E. M.Vlamakisa, X. A.Argyrioua,
N. N. Chatzisavvasa,A. Efdaimona, K. Vagennasa,
P. H. Yannakopoulosa, I. Valaisb, I. Kandarakisb and D. Nikolopoulos
a.TEI of Pireaus b.TEI of Athens
Team:env-hum-comp-res.teipir.gr

2. AIM
X-ray absorption and x-ray fluorescence
properties of medical imaging scintillating
screens via Monte Carlo methods.

3. Introduction
Scintillators are materials which are used as
radiation sensors in medical representation.
Scintillators which were studied:
Scintillator Density
(g cm3)
Gd2SiO (GSO) 4.15
YAlO3 (YAP) 7.40
LuSiO5 (LSO) 6.71
LuAlO3 (LuAP) 7.34

4. Materials and Methods 1
Adequate EGSnrcMP codes were generated
together with other self-developed and validated
Monte-Carlo software.
Parameters studied were (a) scintillator material
and (b) energy of exposure. Energy value studied
was 511 keV. This is the characteristic energy for
positron emission tomography(PET).

5. Materials and Methods 2
EGS
The EGS (Electron–Gamma–Shower) platform is
a general purpose package for the Monte Carlo
simulation of the coupled transport of electrons
and photons in an arbitrary geometry for particles
with energies above a few keV up to several
hundreds of GeV.

6. Materials and Methods 3
Phenomena for EGS simulations:
● Compton scattering
● Coherent (Rayleigh) scattering
● Multiple scattering of charged particles
● Møller and Bhabha scattering
● Continuous energy loss of charged particle tracks between
discrete interactions
● Pair production
● Bremsstrahlung production
● Positron annihilation in flight and at rest
● Relaxation of excited atoms after vacancies are created

7. Materials and Methods 4
PEGS4 code
Generation of mortran codes (Fortran pre
processor) for the input of simulation
parameters
● pegs4dat:definition if the charasteristics of the
material(name,structure etc)
● egsinp:definition of the parameters for how the
simulation is going to be.

8. Materials and Methods 5
The scintillators were modelled as blocks of various
thickness values. A series of thickness values ranging
from 0 to 50 mm were investigated.
Modeled scintillators were considered to be exposed to
x-ray initiating from a point source located at the central
axis of the entrance area of the scintillator block at pencil
beam geometry.
z

9. Materials and Methods 6
Parameters were studied from simulations:
● Quantum Detection Efficiency (QDE) from
every block of scintillator
● Energy Absorption Efficiency(EAE) from every
block of scintillator
● Efficiency of Absorption of Incident Energy
(EAIE)

10. Results and Discussion 1
For the LSO, GSO and LuAP
crystals:
Overall Absorbed-EAIE
increases with increasing crystal
thickness tending to form a
plateau above at 40 mm
thickness. For these crystals this
EAIE at the 10 mm thickness had
the values of 44.8%, 36.9% and
45.7% respectively and 96.4%,
93.2% and 96.9% at the 50 mm
thickness.
For the YAP crystals:
Overall absorbed-EAIE at 511 keV for the Overall Absorbed-EAIE
four scintillators under study. increases continuously in the
whole of the examined thickness
range. The Overall Absorbed-
EAIE of the YAP crystals
presented the values of 16.8% at
the 10 mm crystal thickness and
68.1 % at the 50 mm thickness
respectively.

11. Results and Discussion 2
The Scatter and Reabsorbed-EAIE
increases with crystal thickness.
30
Scatter and Reabsorbed-EAIE:
For LSO crystals:
12.8% 10 mm thickness
20
LSO 59.9%  50 mm thickness
GSO 57-59%  plateau area (40mm)
(%)
YAP
10
For the GSO crystals:
LuAP
22.3%  10 mm thickness
63.5%  50 mm thickness
0 59-63%  plateau area (40mm)
0 10 20 30 40 50
For the YAP crystals:
Thickness (mm) 15.2%  10 mm thickness
26.2% 50 mm thickness
Scatter and Reabsorbed-EAIE at 511keV for 52-63% plateau area (40mm)
the four scintillators under study For the LuAP crystals:
62.9%  10 mm thickness
61.6%  50 mm thickness
58-61%  plateau area (40mm)

12. Results and Discussion 3
For the LSO, GSO, YAP and
LuAP:
QDE was found to be:
10mm
LSO:54.9%
GSO:48.8%
YAP:37.4%
LuAP:56.8%
50mm
QDE at 511 keV for the four LSO:96.4%
scintillators under study. GSO:95.4%
YAP:89.9%
LuAP:96.9%

13. Results and Discussion 4
The shapes of the QDE curves presented similarities to
the corresponding curves of the overall absorbed-EAIE
but they are shifted up to higher values.
This was more strongly observed for the YAP scintillator.

14. Results and Discussion 5
● Results indicated that x-ray absorption and x-ray
fluorescence are affected by the incident photon
energy and the thickness.
● X-ray absorption and fluorescence was found to
exhibit very intense changes near the corresponding
K-edge of the heaviest element in the scintillator.
● Thicker scintillators exhibited higher x-ray absorption
and x-ray fluorescence.
● A significant fraction of the generated x-ray fluorescent
quanta was found to escape from the studied
scintillators.This increased with increase in thickness.

15. Results and Discussion 6
● Most of the incident photons were found to be absorbed
via one-hit photoelectric effect.
● Differences in x-ray absorption and x-ray fluorescence
were found among the various scintillators studied.
● LSO scintillator was found to be the most attractive
material for use in many applications, exhibiting the best
absorption properties in the largest part of the energy
studied.
● Y based scintillators were also found of significant
absorption performance within the low energy ranges.

16. References
● Comparative study using Monte Carlo methods of the radiation detection
efficiency of LSO, LuAP, GSO and YAP scintillators for use in positron
emission imaging (PET) ,Dimitrios Nikolopoulos, Ioannis Kandarakis,
Xenophon Tsantilas, Ioannis Valais, Dionisios Cavouras, Anna Louizi
● Monte Carlo study of the Detection Efficiency of various scintillators for use
in positron emission imaging (PET) ,D. Nikolopoulos, I. Valais, P.Gonias, N.
Bertsekas, S. David, C. Michail D. Cavouras, G.S. Panayiotakis, I.
Kandarakis
● J.M. Boone, J.A. Seibert, J.M. Sabol, M. Tecotzky, Med. Phys. 26 (6) (1999) 905.
● I. Kandarakis, D. Cavouras, Eur. Radiol. 11 (2001) 1083.
● J.M. Bonne, V.N. Cooper, Med. Phys. 27 (8) (2000) 1818.
● J.M. Boone, X-ray production, interaction, and detection in diagnostic imaging, in:
J. Beutel, H.L. Kundel, R.L. Van Metter (Eds.), Handbook of Medical Imaging,
Physics and Psycophysics, vol. 1, SPIE Press, Bellingham, 2000, p. 40.