A Prompt-Gamma-Camera Designed for Monitoring Photon Radiation Therapy

unkindnesskindUrban and Civil

Nov 15, 2013 (3 years and 6 months ago)

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A Prompt
-
Gamma
-
Camera Designed for Monitoring
Photon Radiation Therapy


Joana Gonçalves
1
,
Liliana Sampaio
1
, B
rígida Ferreira
2
, Paulo Fonte
1,3
,

Maria do Carmo Lopes
4
,

Paulo Martins
3
, Paulo Crespo
1,3

1
ISEC
,
2

I3N
-
UA,

3

LIP,

4

IPOCFG,E.P.E.


E
-
mail:
tog_api@hotmail.com
;
lilianasampaio_1@hotmail.com



The
main
goal

of radiotherap
y
(RT)
is
guaranteeing

maximum dose exposure to the
tumour, while maintaining minimum he
althy
-
tissue dosage so to limit undesirable
side
-
effects.

Published studies
document
increasing evidence
supporting
the
existence of responsive biological mechanisms to
the radiotherapeutic injury

[1].
Examples include
edema o
f
the irradiated
region
, tumor

regression, and filling of
empty cavities due to
inflammation and
increased tissue permeability.
Consequently,

changes in the prescribed dose may result. These are highly undesirable if tumor
underdosage or healthy
-
tissue overdosage is induced
.


Modern RT

monitoring
systems seeking the detection

of the aforementioned
morphological changes
are utilized in i
mage guided radiation therapy (IGRT). IGRT
has its own potentialities, limitations
,

and side effects
. E.g.,
an
increased dosage
occurs
in
successive
,

rep
etiti
ve

computerized mega/kilovoltage
imagi
ng [2,3]
.

Within
IGRT limitations, one o
f particular significance is its

inability to
respond with
absolute sensitivity

to
the needs of
RT

monitori
ng
. In order to complement the
relevant clinical information
provi
ded by IGRT
both to

the radiooncologist

and
to
the
patient,
we have deployed an R&D program aiming at assessing
the capability to
monitor
RT

sessions in real time

by means of a dedicated prompt
-
gamma
-
camera
.
This

detect
ion system
must acquire data during
R
T
treatment
s
,
being a
ble
to select
at
the same time
photons that
Compton
-
scattered
in the target (patient) and that are
spatially correlated with the dose. A
dditionally, the system must reject
events
that are
not dose
-
correlated by means of optimized colli
mation, energy windowing, and time
selection
.


Simulation results indicate that
event selection by means of
spatial
collimation
and
energy

discrimination yields
profiles
with scores
highly correlated with the profile of
the prescribed dose
.
This
represe
nts

a potential

asset in ensuring t
he quality of care
administered
. The same simulation results indicate that the poss
ible occurrence of
morpholog
ical changes
during
treatment

can be detected
.

F
i
rst phantom
-
based
experimental data obtained at

IPOCFG, E
.
P
.
E
.

a
re being
analyzed. They reveal the
presence of the expected

dose
-
correlated
physical sign
al. However,

the
existence

of
scattered events
,

so
-
far of unknown origin,
must be addressed
. This is being planned
by means of d
edicated collimation
, op
timized scintil
lation detection, and

signal
processing
at

the
hardware and software

levels
.


References

[1]

Denham JW, Hauer
-
Jensen M
,
Radiother. Oncol.
, vol.
63
, pp.

129
-
45

(2002)

[
2
]

van Elmpt W, M
cDermott L, Nijsten S et al,

Radiother. Oncol., vol.

88:3
, pp.

289
-
309

(
2008)

[
3
]

Thieke C, Malsch U, Schlegel W, Debus J, Huber P, Bendl R, Thilmann C
,
Br. J. Radiol.
, vol.

79
,


pp.
79
-
86

(2006)