Study of the fragmentation of Carbon ions for medical applications

1
Study of the fragmentation of Carbon ions for
medical applications
Giovanni De Lellis Napoli University
Protons (hadrons in general) especially suitable
for deep-sited tumors (brain, neck base,
prostate) and fat people
2
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
3
Carbon beam
Same energy deposit profile as protons but with
larger energy loss per unit length
one ionization every 10nm (DNA helix
2nm)
4
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

5
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

6
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 ions
• Lexan ? 1.15 g/cm3 and electron density 3.6
  x 1023/cm3
• e.g. Water 3.3 x 1023/cm3

Cell structure
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.)
7
Carbon exposure at HIMAC (NIRS-Chiba)
8
C ions angular spectrum
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
Slope Y
Slope X
3.4 cm2 scanning in each sheet (all sheets
scanned)
9
Vertex reconstructionAbout 2300 vertices analyzed
C
3 cm
10
Impact parameter distribution
Helium tracks
Hydrogen tracks
µm
µm
11
Track volume sum of the areas of the clusters
belonging to the track
one sheet R0 type
one sheet R1 type
Z gt 2
?
BG, mip
p
Z gt 1
Upstream sheet
Upstream sheet
p
Downstream sheet (about 5 cm)
Downstream sheet (about 5 cm)
12
R0 vs R1 and R1 vs R2 scatter plot
He
He
H
13
Charge identification
5 R1 VS 5 R2 (2 cm)
10 R1 VS 10 R2 (4 cm)
Z 4
Z 3
Z 2
20 R1 VS 20 R2 (8 cm)
15 R1 VS 15 R2 (6 cm)
Z 5
Z 3
Z 6
Z 4
Z 2
14
Charge separation
Journal of Instrumentation 2 (2007) P06004
15
Charge distribution of secondary particlescharge
reconstruction efficiency
Inefficiency ?Charge 0 Charge efficiency
(2848-27)/2848 99.10.2
16
Carbon interaction
Track multiplicity
Bragg peak
Contamination at the level
17
Angular distribution of secondary particles
Hydrogen
Elastic scattering
large angle (a few percent)
Lithium
Helium
18
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

Toshito et al.
Toshito et al.
Toshito et al.
19
Interaction length for different secondary ions
20
Very preliminary
He-proton opening angle

• 8Be ? He He (10-16 s)
• Q value 90 keV

He
?
He
Real event
? (rad)
21
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 measurement

Possible improvements

• Improve the identification capability for short
  tracks
• Measure the momentum for isotope discrimination
• Extend the energy range for cross-section
  measurements