Study of the fragmentation of Carbon ions for medical applications
Protons (hadrons in general)especially suitable for deep-sited
tumors (brain, neck base, prostate)and fat people
Giovanni De LellisNapoli University
Dose modulation
From the overlap of close peaks (close energies), a conformational
profile is obtained
The patient is rotated so to avoid a long exposure time of the
healthy tissues
Size of the sick part
Carbon beam
Same energy deposit profile as protons but with larger energy loss per unit length
one ionization every ~ 10nm
(DNA helix ~ 2nm)
Charge and mass measurement
• Density of energy along the track path Z2
• Multiple scattering or magnetic field provides either p or p
• From the combined measurement, we can get p and the mass A,Z
Open issues•Knowledge of the Carbon cross-section with human tissues•In particular the exclusive cross-section in the different channels so to predict the detailed irradiation of the neighboring tissues optimization of the therapy with higher effectiveness
Facilities in Europe
• Typically joint beam (physicists) and therapeutic (biological, medical) facilities.
• In Europe, a high energy (few hundred MeV/nucleon) carbon beam is at GSI, Darmstadt, Germany
• In Italy (Pavia, close to Milan) the CNAO under construction, starting on 2009
• Proton centers more numerous• In Italy (linked with INFN) one proton center
operative in Catania, Sicily
Exposure of an ECC to 400 Mev/u Carbon ions
ECC structure: 219 OPERA-like emulsions and 219 Lexan sheets 1 mm thick (73 consecutive “cells”)
exposed to 400 Mev/u Carbon ionsLexan: = 1.15 g/cm3 and electron density = 3.6 x 1023/cm3
e.g. Water 3.3 x 1023/cm3
Cell structure
LE
XA
N
LE
XA
N
LE
XA
N
R0 R1 R2
R0: sheet normally developed after the exposure
R1: sheet refreshed after the exposure (3 days, 300C, 98% R.H.)
R2: sheet refreshed after the exposure (3 days, 380C, 98% R.H.)
Carbon exposure at HIMAC (NIRS-Chiba)
C ions angular spectrum
Slope X
Slo
pe
Y
slope X
(3 )
slope Y
(3 )
P1-0.150 ±0.004
-0.003 ±0.005
P2-0.017 ±0.004
-0.002 ±0.005
P3 0.134 ±0.004
-0.001 ±0.005
3.4 cm2 scanning in each sheet (all sheets scanned)
Vertex reconstructionAbout 2300 vertices analyzed
C
3 cm
Impact parameter distribution
Hydrogen tracks Helium tracks
µm µm
Track volume: sum of the areas of the clusters belonging to the track
BG, mip
Z > 1
p
Upstream sheet
Downstream sheet(about 5 cm)
p Z > 2
one sheet – R0 type one sheet – R1 type
Downstream sheet(about 5 cm)
Upstream sheet
R0 vs R1 and R1 vs R2 scatter plot
H
He
He
Charge identification
Z = 2
Z = 3
Z = 4
5 R1 VS 5 R2 (2 cm) 10 R1 VS 10 R2 (4 cm)
15 R1 VS 15 R2 (6 cm)
20 R1 VS 20 R2 (8 cm)
Z = 4
Z = 3
Z = 2
Z = 5
Z = 6
Charge separation
Journal of Instrumentation 2 (2007) P06004
Charge distribution of secondary particlescharge reconstruction efficiency
Inefficiency Charge = 0Charge efficiency = (2848-27)/2848 =
99.1±0.2%
Carbon interaction
Bragg peak
Contamination at the % level
Track multiplicity
Angular distribution of secondary particlesElastic scattering Hydrogen
Helium
large angle (a few percent)
Lithium
Cross-section measurement• A volume of about 24cm3 was analyzed
• 2306 interaction vertices found (475 elastic)
• The number of events with maximal charge as Lithium (z = 3) is 183, as beryllium (z = 2) is 118, as Boron (z = 1) is 258
( 1) 2330 150
( 2) 1060 100
( 3) 1650 120
z mbarn
z mbarn
z mbarn
Toshito et al.
Toshito et al.Toshito et al.
Interaction length for different secondary ions
14.0 1.2H mm 14.0 1.2H mm
14.0 1.2H mm
14.0 1.2H mm 19.3 2.3He mm
Very preliminary• 8Be He + He (10-16 s) • Q value 90 keV
8( ) 225 50C Be mbarn
(rad)
He
He
Real event
He-proton opening angle
Conclusions• The charge separation capability is about 5 sigma
for protons and helium already with less than 10 plates where other detectors fail
• The separation between boron and carbon requires 30 plates to reach 2.5 sigma
• Emulsions provide unprecedented results in the light ion identification
• Preliminary results cross-section measurementPossible improvements
•Improve the identification capability for short tracks•Measure the momentum for isotope discrimination•Extend the energy range for cross-section measurements
