Il progetto di mammografia clinica con luce di …sirr.casaccia.enea.it/Congressi SIRR/Present-SIRR...La radiografia convenzionale si basa sulle caratteristiche di assorbimento del

XIV Convegno SIRR – Trieste, 24-27 giugno 2008Giuliana Tromba1

Il progetto di mammografia clinica

con luce di sincrotrone:

aspetti fisici e dosimetrici

Giuliana TrombaSincrotrone Trieste

per la Collaborazione SYRMEP


Ospedale di

Cattinara

Il laboratorio ELETTRA


Sommario

� I vantaggi della luce di sincrotrone

� La linea di luce SYRMEP

� Il progetto di mammografia clinica con luce di sincrotrone

� Le problematiche di sicurezza e radioprotezione per la paziente e gli operatori

� Il sistema di monitoraggio della dose in ingresso• Funzionalità e caratteristiche

• Metodi di calibrazione e risultati ottenuti

� Il sistema di gestione dell’esame (Supervision and Human-Machine Interface system)

� Il protocollo di esame

� Il confronto delle dosi

� Conclusioni e prospettive future

XIV Convegno SIRR – Trieste, 24-27 giugno 2008Giuliana Tromba

Perchè utilizzare la luce di sincrotrone nell’imaging bio-medicale?

• Monocromaticità ottimizzazione dell’energia dei raggi X

(riduzione della dose)

CT e µCT con valutazioni quantitative sulla densità

utilizzo di mezzi di contrasto

assenza di beam hardening

• Coerenza spaziale applicazione di tecniche di imaging sensibili alla

fase

• Collimazione assenza di scattering

• Alta intensità riduzione del tempo di esposizione

Queste caratteristiche portano ad un miglioramento dell’immagine eduna riduzione della dose assorbita

XIV Convegno SIRR – Trieste, 24-27 giugno 2008Giuliana Tromba 5

La radiografia convenzionale si basa sulle caratteristiche di assorbimento del campione. Il contrasto

è generato dalle variazioni di composizione, densità o spessore del campione (variazione di β).

La tecnica del contrasto di fase è sensibile anche allo sfasamento dei raggi X che attraversano il

campione (variazione di δ). Il contrasto nell’immagine è prodotto dai phase shifts prodotti dal campione sul fronte d’onda entrante. Effetti di edge enhancement.

Intensity

incom ingwave

x

yz

transm ittedwave

c

objectαααα

αααα11110000 ∼∼∼∼<<<< 111100000000 ∝∝∝∝rad∼∼∼∼<<<<

distorted wave

incom ingwave

x

yz

object

interference

Conventional radiology PHC

PHasePHase--Contrast (PHC)Contrast (PHC) imagingimaging

(∆∆∆∆I/I)abs

= e s ∆µ∆µ∆µ∆µ – 1

n = 1 - δ - iβ : refraction index

µµµµ = 4π β / λ : linear absorption coeff.

s : object size // to beam direction

∆φ∆φ∆φ∆φ = 2ππππ s ∆δ∆δ∆δ∆δ / λλλλ


PhCPhCConvenzionaleConvenzionale

PhC a SYRMEP


Progetto finanziato da Fondazione CRTrieste

Scopo: Esami di mammografia su un campione selezionato di pazienti

Target: Seni densi e/o disomogenei;

mammografia convenzionale con diagnosi incerta;

sospetto di falsi positivi.

Modalità: I Fase: radiografie planari con rivelatori commerciali;

II Fase: tomografia

Il progetto SYRMA (SYnchrotron Radiation for MAmmography)

Convenzione tra: Azienda Ospedaliera mista, Università di Trieste, Sincrotrone

Inizio sperimentazione: 13 marzo 2006


Preparazione del fascio(energia, beam shape, filtri) Controllo del fascio

(monitori di dose, shutters)

Sala pazienteSala radiologo

SALA CONTROLLO

FLTPSBSMONOSLITS

IC1 IC2SSH

CON1

PR

Patient

Detector

EXP

CON2

La linea SYRMEP

Sistemi di sicurezza:• Sist. di controllo accessi (per il personale)• Sist. di controllo della dose (per la paziente)Caratteristiche: ridondanza, diversificazione dei componenti


Componenti di sicurezza: dosimetri e shutters

IONIZATIONCHAMBER 2IONIZATION

CHAMBER 1

SAFETY SHUTTER 1

SAFETYSHUTTER 2

IMAGINGSHUTTER


Posizionamento della paziente

tomographytomography

mammographymammography


La sala radiologo


Sala paziente


Il supporto della paziente


Il sistema di compressione

Patient support

Hole axis

Beam

Manual Motorized

ReferenceReleasing

CompressionDecompression


Il supporto del detector

Screen-filmcassette

Fixedshield

Entrance slit

Antiscattering shield

Beam


Safety Laser Scanner

• System by Schmersal based on laser IR diode (905 nm)

• Used to prevent collisions and protect personnel from X-ray unwanted exposure

• It recognizes two maps:• collision zone• X-ray hazard

• It can handle two possible interventions (pre-alarm and alarm)


• It determines access conditions to the patient hutch

• Based on Pilz PS 3000 PLC with high safety standard

• Operating modes: experiment and patient– Experiment mode (i.e. standard

beamline: door locked, standard search procedure required to open beamstoppers, etc.)

– Patient mode: ‘Radiologist’ key inserted, door unlocked, modified search inspection)

The Patient Access Control System (PACS)

CPU & I/O


• It operates in patient mode

• Aims:

– to prevent over-exposure to the patient

– to monitor the correct working conditions of all the components before and during a scan

• Alarm states:

– Malfunction of dose monitors

– Malfunction of support or film systems

– Mismatch of monochromator energy

– Overcome of skin doserate threshold

– Overcome of integrated dose threshold

• Actions:

– Abort of exam: closure of safety and imaging shutters

– Acoustic alarm

The Dose Control System (DCS)


• Aims:

– to provide continuous dose monitoring during patient scan

– to optimize the X-ray beam (monochromator crystals

rocking) before each patient examinations

• Characteristics:

– Non destructive measurements

– Redundancy (IOC1, IOC2)

– High stability and reliability, wide dynamic range

– Quick response, unsensitivity to small vertical displacement of the X-ray beam

The dose and beam monitors


• Ionization chambers:

– Sensitive volume: 2 regions, 12.5 mm thick

– Central electrode and windows

– Electrodes, entrance and exit windows perpendicular to the beam realized in mylar foils 50 µm thick covered on each side by an Al layer 50 nm thick.

– Central electrode area: 238 mm x 56 mm

The dose and beam monitors hardware


– The analog part of the readout electronics is placed within a sealed housing to minimize external electromagnetic pick up.

– The electronics integrates the charges released in the conversion gas over a predefined integration time.

– Readout is based on a commercial available integrated circuit (DDC112 from Burr Brown). 20 bit A/D convertion.

– A micro controller is used to generate the necessary initialization signals for the DDC 112 and to set the integration timing (from 0.5 ms to some s). 7 different gains can be set (ranging from 50 pC – 350 pCfull scale range)

– Integration time = 1 msec;

– The precision of the air kerma measurements is improved considering the average value of IOC readings in 1 sec, typically 1000.

– Gain = 50 pC (to assure a high sensitivity even for low currents measurements avoiding at the same time a possible saturation for the maximum available current at the beamline). 50 pC is the maximum interated charge measured current of 50 nA for an integration time of 1 msec).

The dose and beam monitors electronics


– Response stability

• Measurements with respect to the Standard free air chamber in the National laboratory for ionizing radiation metrology (ENEA-INMRI lab) using calibrated sources

– Linearity of response

• Measured current is proportional to the beam horiz. dimension

– Saturation curve

– Ion ricombination (method by Boutillon*)

– Uniformity of response

• Over the sensitive volume the IC shows the same response

Preliminary dose monitors characterization

* M. Boutillon, “Volume recombination parameter in ionization chambers”, Phys.Med.Biol. 43, 2061-2072, 1998


Calibration of dose monitors

• Absolute air-kerma measurements have been performed using the ENEA-INMRI

National Standard (NS) free-air chamber for low energy X-rays.

• NS was positioned on the patient support at the place of the breast and was equipped

with a 1.5 mm radius diaphragm.

• Beam horizontal dimension (defined by the patient slits): 1 cm.

• Simultaneous measurements have been taken by IOC1, IOC2 and NS.

• Calibration factors take into account T and P conditions

• The photon attenuation in air was accurately determined using a vacuum tube of about

200 mm length in which the air pressure was varied down to 10-3 kPa


Measurements with the Secondary Chamber• Periodical calibration of dose monitors is performed through a Secondary free

air Chamber (SC). SC was not designed for absolute measurements but in order

to have a long term stability. It accepts the same 1.5 mm radius diaphragm of

NS. SC was positioned in the same position of NS.

• Beam horiz. dimension (defined by the patient slits): 1 cm.

• Simultaneous measurements have been taken by IOC1, IOC2 and SC.

• Calibration factors take into account T and P conditions


Evaluation of patient entrance air kerma

The air-kerma rate as measured by the NS chamber is given by:

∏−

=i

ikge

W

V

IK

air

air

air 1

1

ρ&

Where:

ρair = density of air under reference conditions,

V = chamber measuring volume,

I = ionization current,

Wair = mean energy expended by an electron of charge e to produce an ion pair in air,

gair = fraction of the initial electron energy lost by bremsstrahlung production in air,

Πki = product of the correction factors to be applied to the SC

iIOCiIOC FIK ⋅=&

Calibration factors F for IOCi is given by:


5.0E-08

1.5E-07

2.5E-07

3.5E-07

4.5E-07

5.5E-07

6.5E-07

7.5E-07

8.5E-07

9.5E-07

1.1E-06

1.2E-06

8 10 12 14 16 18 20 22 24

E (keV)

F IO

C (

Gy/u

.a.)

F IOC1 TPN

F IOC 2 TPN

Calibration factors for IOC1 and IOC2 vs. X-ray energy


Calibration factors for SC respect to IOCi vs. X-ray energy

5.65E+08

5.70E+08

5.75E+08

5.80E+08

5.85E+08

5.90E+08

5.95E+08

6.00E+08

6.05E+08

6.10E+08

5 7 9 11 13 15 17 19 21 23 25 27 29 31 33E (keV)

Fsec (

Gy/C

)

Fsec(IOC1)

Fsec(IOC2)


The Supervision and Human-Machine Interface (SHMI) system

• Functions:

– Insert initialisation/calibration data

– Register patient data

– Select the X-ray energy and optimize the beam through the

Beamline Control System

– Control the congruency of all the examination parameters

– Manage the pre-scan

– Carry out the scan

– Register dose report


Exam initialization• Input of patient parameters,• Choice of X-ray energy (according to the breast thickness and on

an estimate of breast glandularity class (i.e. low, medium, high)),• Beam optimization.

Prescan• It is a scan over a small breast portion in a range selected by

radiologist.

• It aims to measure the breast absorption properties and to evaluatethe real breast glandularity.

• The results of prescan are used to confirm the choice of the X-ray energy and to calculate the scan speed.

• The delivered dose is 5-10 % the examination dose.

Exam

• The exam is a simultaneous scan of breast and detector in a range selected by radiologist.

Examination Protocol


Examination protocol: pre-exposure

I0I1

Attenuation coefficientGLANDULARITY

Ionization chamber

Exposimeter

Slightly compressed breast

Beam

SelectedMeasuredCalculated

BREASTGlandularity class

THICKNESSPRE-SCAN SPEED

ENERGYFLUX

Film is removed from the beam


THICKNESSGLANDULARITY

ENERGYFLUX

SCAN SPEEDSelectedMeasuredCalculated

BeamFilm/screen

Compressed breast

Examination protocol: exposure


Pat. 8 - 164839 – GA – CC RIGHT s

Synchrotron radiationConventional unit



Average Entrance Skin Doses delivered to patients at SYRMEP and at the conventional mammographic unit (Senographe GE)

Vertical bars indicate the data distribution of each thickness class

0

2

4

6

8

10

12

0 2 4 6 8 10

Breast thickness (cm)

Dose (m

Gy)

SYRMEP

SenographeGE

Doses comparison I


0

1

1

2

2

3

0 1 2 3 4 5 6 7 8 9

Breast thickness (cm)

Dose (m

Gy)

SYRMEP

SenographeGE

Average Mean Glandular Doses delivered to patients at SYRMEP and at the conventional mammographic unit (Senographe GE)

Vertical bars indicate the data distribution of each thickness class

Doses comparison II


First protocol of clinical mammography with SR is started.

– Promising results obtained on the first 46 patients:

• Safety and Supervision systems show high reliability and efficiency.

• ESDs and MGDs are lower than the ones of conventional clinical unit,

improved image quality (contrast & spatial resolution).

– Patients are easily recruited, no negative reactions.

– Need to implement soon:

• a digital detector (to improve image, increase the X-ray energy, reduce

dose, phase retrieval…etc).

– Challenging upgrades:

• use of tomosyntesis/tomography to recognize the lesions overlap.

Conclusions and perspectives


A.Abrami, K.Casarin, V.Chenda, D.Dreossi, R.H. Menk, E.Quai, A.VascottoSincrotrone Trieste

F. Arfelli, E. Castelli, R. Longo, L. Rigon, T. Rokvic(*), E. VallazzaDipartimento di Fisica, Università di Trieste e INFN, Sezione di Trieste

(*)Anche al Dipartimento di Fisica, Università di Belgrado

M.A. Cova, E. Quaia, D. Sanabor, M. Tonutti, F. ZanconatiDip. Univ. Clinico di Scienze Cliniche, Morf. e Tecnologiche, Università di Trieste

P. BregantStrutt. Complessa di Fisica Sanitaria, Az. Osp.- Universitaria ‘Ospedali Riuniti di Trieste’

M. Bovi, F. Laitano, M.P. ToniIstituto Nazionale di Metrologia delle Radiazioni Ionizzanti, ENEA - CR Casaccia

Acknowledgements

Grazie per l’attenzione

Documents

Il progetto di mammografia clinica con luce di …sirr.casaccia.enea.it/Congressi SIRR/Present-SIRR...La radiografia convenzionale si basa sulle caratteristiche di assorbimento del