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