ON-LINE MONITORING OF AN HADRON BEAM FOR RADIOTHERAPEUTIC TREATMENTS INFN-Laboratori Nazionali del Sud Via S. Sofia 44, Catania, Italy Patient positioned for treatment System under consideration (experimental configuration) G.A.P. CIRRONE, S.COCO, G.CUTTONE, C. DE MARTINIS, D. GIOVE, P.A. LOJACONO, M. MAURI, R. MESSINA
AT LABORATORI NAZIONALI DEL SUD (CATANIA), CATANA FACILITY (Centro di AdroTerapia e Applicazioni Nucleari Avanzate) employs a 62 MeV proton beam, produced by a superconducting cyclotron, for the radiotherapeutic treatment of choroid and iridal melanoma. The main requirement for a successful treament is: ACCURACY in the spatial distribution of thedosereleased to skin guaranteed by numerous experimental checks Patient positioned for the treatment
ROUTINE BEAM MONITORING SYSTEMS DIODE: transversal scanning of the beam by means of a silicon diode which measures the current and displays its distribution along the two coordinates of a Cartesian system, transversal to the beam direction; GAFCHROMIC FILM: determination of the lateral dose distribution released by the beam from the darkening of an irradiated gafchromic film; both systems, though very accurate, are subject to long acquisition and processing times Acquisition period ~30 minutes Acquisition period ~24 hours
DEVELOPED SYSTEM HADRON BEAM SCINTILLATING SCREEN 45 MIRROR monitoring system of a hadron beam based on a fluorescent screen coupled with an analog CCD camera; acquisition and processing of the image reflected by the mirror by means of a software application implemented with LabVIEW 6.1; CCD LabVIEW Acquisition period ~ 1 minute
TESTED SCINTILLATORS Alumina (Al2O3) Caesium Iodide (CsI) Plastic scintillator BC 400 Alumina: poor in light efficiency; Caesium Iodide: excellent light efficiency, but scarce homogeneity; BC 400: good brightness and homogeneity; BC 400 has been chosen for our experimental purposes.
FINAL CONFIGURATION Mirror forming 45 with the beam direction. Scintillating screen lodged on a support, perpendicularly to the beam axis. Camera forming 90 with the beam axis, framing the image reflected by the mirror.
DATA ANALYSIS High quality monochrome image acquisition board: IMAQ PCI-1409 (National Instruments) Acquisition and memorization of signal in the form of 10 bits matrices Spatial coordinates of each pixel of the camera Corresponding grey-scale values
SOFTWARE FOR DATA ANALYSIS LabVIEW Environment Spatial calibration Cartesian reference system Calibration factor: 0.112 mm/pixel Selection of the Region Of Interest
SOFTWARE FOR DATA ANALYSIS LabVIEW Environment NOISE REDUCTION: average of N images EXPERIMENTAL SIGNAL ACQUISITION BACKGROUND SUBTRACTION
SOFTWARE ANALYSIS Acquisition and analysis of lateral profiles signal % 100 90 80 W 50 % 60 H 90/50 % 40 20 Psx distance from axis (mm) Pdx Remote communication, through the intranet, between the application and the accelerators console
FRONT PANEL OF THE VI LabView Environment
BLOCK DIAGRAM OF THE VI LabView Environment
3D-GRAPH
CHARACTERIZATION OF THE SYSTEM LINEARITY SIGNAL TO NOISE RATIO SNR vs sqrt(frames) 300 250 Equazion: y = A*x + B A = 30.03107 ± 0.63571 B = 10.58847 ± 2.77585 200 R 2 = 0.99421 SNR 150 100 Experimental data linear FIT 50 0 0 2 4 6 8 sqrt (frames) Linearity in the treatment range (10 20 Gy/min) Castleman says: SNR (N)= N^0.5*SNR(1) Experimental results are in good agreement with theoretical considerations
CHARACTERIZATION OF THE SYSTEM CONTRAST SPATIAL RESOLUTION Background subtraction upgrades image contrast of a factor 2 Given: MTF = 0.3 Spatial resolution is : 2.22 mm/lp
EXPERIMENTAL RESULTS AND COMPARISONS signal % 120 100 80 60 40 20 CCD - DIODE COMPARED PROFILES diode CCD 0-20 2-15 -10-5 0 5 10 15 20 Peculiar parameters of a lateral beam profile, calculated with the two systems,are in a good agreement CCD diode ratio 0 profile ratio -20-15 -10-5 0 5 10 15 20 distance from axis (mm) X AXIS W50% (mm) H 90/50% Psx (mm) Pdx (mm) CCD 50 FRAMES 25.88 0.90 1.50 1.50 DIODE 25.97 0.91 1.46 1.48 DIFF.% -0.38-0.86 2.75 1.12
EXPERIMENTAL RESULTS AND COMPARISONS
CONCLUSIONS AND EXPECTATIONS Comparable results with those obtained through currently used systems Remarkably reduced times of data acquisition and processing Potential employment of the system as a fast and accurate instrument of: beam centering (directly used by cyclotron operators) beam monitoring In the future, the use of thinner scintillating materials is expected, in order to overcome some scattering phenomena which affect spatial resolution.
CHARACTERIZATION OF THE SYSTEM MODULATION TRANSFER FUNCTION INPUT MODULATION OUTPUT MODULATION
CHARACTERIZATION OF THE SYSTEM MODULATION TRANSFER FUNCTION PATTERN METHOD IDEALLY: SINUSOIDAL WAVES OF SAME AMPLITUDE AND DIFFERENT FREQUENCY ACTUALLY THE IMAGING SYSTEM MODIFIES THE SIGNAL SINUSOIDAL WAVES OF DIFFERENT AMPLITUDE AND FREQUENCY
CARATTERIZZAZIONE DEL SISTEMA MODULATION TRANSFER FUNCTION FOURIER TRANSFORM GIVEN A FUNCTION: FOURIER TRANSFORM IS: EXAMPLE: FOURIER TRANSFORM IS: GIVEN THE FOURIER TRANSFORM H(f), THE INVERSE OPERATION, CALLED ANTITRANSFORMATION, GIVES THE BEGINNING FUNCTION: SUM OF INFINITE SINUSOIDAL AND COSINUSOIDAL FUNCTIONS OF DIFFERENT AMPLITUDES AND VARYING FREQUENCIES
CHARACTERIZATION OF THE SYSTEM MODULATION TRANSFER FUNCTION SLIT METHOD: IDEALLY: AN IDEAL SLIT CAN BE SEEN AS THE SUM OF INFINITE COSINUSOIDAL FUNCTIONS OF DIFFERENT FREQUENCIES, BUT SAME AMPLITUDE CONSTANT: ACTUALLY: GAUSSIAN CURVE: SUM OF INFINITE COSIDUSOIDS OF DIFFERENT FREQUENCIES AND AMPLITUDES DECREASING WITH FREQUENCY:
CARATTERIZZAZIONE DEL SISTEMA MODULATION TRANSFER FUNCTION EDGE METHOD: IDEALLY: ACTUALLY:
CHARACTERIZATION OF THE SYSTEM MODULATION TRANSFER FUNCTION Pattern Edge
CHARACTERIZATION OF THE SYSTEM CONTRAST Definizione e figura Johns
DEVELOPED SYSTEM HADRON BEAM MIRROR 45 SCINTILLATING SCREEN CCD LabVIEW