r.g. figueroa 1, m. valente 2 1 departamento de cs. físicas, universidad de la frontera, temuco...
TRANSCRIPT
Dose Calculation Distribution for in-vivo X-ray Fluorescence Scanning
R.G. Figueroa1, M. Valente 2
1 Departamento de Cs. Físicas, Universidad de La Frontera, Temuco Chile2 Universidad Nacional de Córdoba, Córdoba, Argentina, E-mail: [email protected].
Outlines
Motivation Materials and Methods Results Conclusions
Motivation
OUR GOAL: To assess the in-depth dose distribution within human-like phantom for in-vivo scanning XRF applications.
Motivation
The spatial distribution and concentration of chemical elements in different organs and bone, might be an indicator of certain diseases or be out of the tolerable levels, therefore :
The knowledge of the concentration of elements and their spatial distribution may provide important information regarding the health of an individual.
In vivo X-ray fluorescence analysis has been used since 1976, which allows the detection of elements present in the body, that could be the cause of certain diseases.
Some effects on human health
High levels of copper (Cu) have shown to be directly correlated with different cancer diseases. Elevated copper levels have been found in malignant cells, in concentrations that range from 1.5 to 3 times higher, compared to their normal values.
Lead (Pb) is one of the most studied elements. An increased level of Pb can cause different diseases in human health
A high concentration of Strontium interferes with the mechanism of calcification of bone matrix, among other effects
Some effects on human health
The serum iron (Fe) levels in the blood can also determine severity of thalassemia.
Mercury (Hg) is a toxic and nonessential element for humans, which can cause poisoning by concentration.
Zinc (Zn) is an essential mineral for human growth, important for bone mineralization. Zinc compounds may be a new drug in the treatment of osteoporosis.
Calcium (Ca) and phosphorus (P) are the main mineral components of bone tissue.
Dose Calculation
In order to implement any kind of radiation therapy or
diagnosis, it is mandatory to suitably perform preliminar dose delivery estimations.
In this case it is necessary to carefully establish energy deposition and radiation damage potentiality for a low energy (some tens of keV) photon beam irradiating a human-like phantom.
All interaction mechanisms have to be considered, however photoelectric and Compton effects along with elastic scattering are the most relevant ones.
Mecanismos de Interacción
Photoelectric EffectCompton scatteringRayleigh scatteringPair (e--e+) production
More relevant effects: Photoelectric Compton Rayleigh
]/[ 2 gcmu
u CRM
0
Mass absorption coefficients
Irradiated material: tissue-equivalent water-equivalent (International Protocols TRS-398)
Photoelectric effect as predominant interaction mechanism.
Irradiation beam as pencil kernel (high collimated) beam Calculation based on absorbed primary
particles at thickness dx position at depth x. Model: Lambert Law
]/[)1()( 20 gcmeNxN x
NLN0
dxx
L
Dosimetry calculation model: suitable approximations
X-ray tube according to in-vivo scanning ubo XRF system
Collimators (from 0,1 to 2,0 mm diameter)
0 5 10 15 20 25 30 35 40 450E+00
1E+08
2E+08
3E+08
Energy [keV]
Inte
nsi
ty [f
/s]
Incident Spectrum
Mean (macroscopic) dose value as energy per unit mass
]/[)(0
2
KgJdEdmdE
NdE
dm
dExD
MaxE
]/[)1(
)(0
)(2
0 KgJdEdEdxA
edEEN
MaxE xE
Mass Absorbed dose calculation
Incident spectrum represented as a sequence of piecewise continuous and weighted contributions (dE E)
Macroscopic thickness: intervals of lengths (dx x(=1mm))
Energy tallied within x thickness of section A
Method “pencil beam”.
]/[)1(
)()(10
)(
0 KgJxA
eEEN
m
ExD
Max iN xE
ii
Absorbed dose calculation: suitable approximations
Collimated incident beam Irradiated surface: plane Irradiated material: homogeneous
(water)
Geometric arrangement and irradiation set up
Incidente beam: collimated and normal
Irradiated surface: smooth Irradiated phantom: Heterogeneous
Skin Muscle (skeletal) Bone (compact)
Geometric arrangement and irradiation set up
In-depth dose distribution for homogeneous (water-equivalent) phantom
0 0.5 1 1.5 2 2.51
10
100
Depth Dose
L
Profundidad [cm]
Dosis
[µGy
]
Preliminary dose estimation: Results
In-depth dose distribution for heterogeneous (skin-muscle-bone) phantom
0 0.5 1 1.5 2 2.51.0
10.0
100.0
Depth Dose
Profundidad [cm]
Dosis
[µGy
]
Preliminary dose estimation: Results
Materials and Methods
XRF Spectrometer A robotic arm Electronic & software control Geometry Scanning Area XRF image acquisition Samples
XRF Spectrometer
1 mini X-ray tube (MXRT)
A digital pulse processor with MCA
A detector SDD (Silicon Drift Detector)
Robotic arm
A robotic arm which positions the detector and the Mini-X at 90º and 45º from the horizontal (x, y) of the sample
Electronic & software control
An electronic control software for the mechanical x,y system and image processing, which allows you to select the step and acquisition time at each point.
MTRX-sample distance is 1.3 cm , approximately
sample-SDD distance is 1.5 cm approx.
Geometry
Scanning area
Each scan is defined as the area of interest shape and size of the sample
The maximum 100x100 mm2, variable spatial resolution that can reach 0.1 mm2 per
pixel, according to the step and diameter collimation The step ranges from 0.1 mm to 50 mm with a
minimum of XRF spectral capture up to 1 ms per point, with 256 energy channels.
The XRF robotic system
Control
Amp+ADC
Shifter x, y
X-ray tubeDetector SDD
Sample
PC: Control SoftwareData Acquisitions
Mechanical part
Firmware and Electronic
Arm
Samples
1. Human bones: phalanges, patella, femur, fibula and jaw
2. Animal: gallus gallus legs, Rat Kidney
3. Blade-bone4. Biological material equivalent
to bone-tissue, including pure solids and standards for calibration.
Esamples:Human hand images
Hand Skeleton images analysis (optical), top left, together with the corresponding XRF elemetal images of the Ca, P, Fe, Zn detected in the skeleton of a human hand.
Ca P
Fe Zn
Example: hand
Integrated XRF spectrum of the human hand skeleton, here shown the presence of 14 elements.
Collimator size effect sample: phalangeal joint
collimation effects in the XRF image obtained in a phalanx bone, calcium element
0.75 mm0.50 mm 1.00 mm 1.50 mm
Rat kidney
Visible and XRF+ Background images
Rat kidney
TiK
As Cl Cu
Fe
Conclusions
Ha sido posible determinar la dosis en un caso particular a que estaría sometido un paciente que experimente un analisis XRF en vivo mediante barrido .
The system….
your attentionThanks for
Acknowledgements
Thanks to the National Fund for Scientific and Technological Research (FONDECYT) of Chile, which has funded this work through Project 1080306 and Morphology Unit, Department of Basic Sciences, University of La Frontera for providing bone samples used in this work.
And……