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: figueror@ufro.cl. 

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.

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