Physics of carbon ions and principles of beam scanning

G. KraftBiophysik, GSI, Darmstadt, Germany

PTCOG43 Educational Satellite Meeting: Principles of Carbon Ion Therapy December 9th,2005 GSI,Darmstadt

Physical and technical features of proton and carbon beams

– Inverse depth dose profile

– Lateral scattering and dose gradients

– Intensity modulated beam delivery

– In vivo PET control of the beam

– Extension to moving targets

Depth dose distribution of various radiation modalities

fragmentation of heavy ions

Comparison of dose profiles of

protons and carbon

Lateral Scattering

Edge effect; overrange induced by scattering

Treatment Plan with edge effects

O. Jaekel et al. , DKFZ

Scattering and irradiation geometry

Beam scattering for a real scanning setup

(exit window, monitors, air, patient)

vacuumwindow

monitors air skin patient

FW

HM

(mm

)

U. Weber 2002

Comparison of Carbon Ions vs. Protons

C-12 (GSI) Protons (Capetown/SA)

Advantage due to beam scanning and less lateral scattering

Passive beam modulation

CASE 2

• BENIGN MENINGIOMA (recurrence after 2 surgeries) with invasive growth in the lateral and upper aspects of left orbit displacing the optic nerve

PRESCRIPTION:

AVERAGE DOSE to PTV (CTV + 3 mm) = 56 Gy 

IMRT

C ionsp+ passive

p+ active

Pituitary Lacrimal gland

BrainPTV

Vol.(%)

Vol.(%)

Vol.(%)

Vol.(%)

Dose (Gy)Dose (Gy)

ScattScatt

ScattScatt

Dose (Gy) Dose (Gy)

Principle of raster scanning

Image of Albert Einstein produced with the GSI rasterscan system using a 430 MeV/u carbon beam of 1,7 mm width (FWHM). The picture consists of 105x120 pixel filled by 1.5.10 10 particles given in 80 spills (5 sec. each) of the SOS accelerator. Original size of the picture: 15 x 18 cm

Slices of a tumor treated at GSI

Active Rasterscanning and Monitoring

Rasterscan: Online- Monitor

Intensity distributon in a sphere

Intensity distribution of one slice

Clival Chordoma

O. Jaekel et al. , DKFZ

Positron Emission Tomography (PET)

In situ control with PET

Verifying the position of the irradiation field

dose plan

measured simulated

W.Enghardt et al. , FZR Dresden

precision of stereotactic fixation:

1mm in the head to3mm in the pelvic region

not feasible for regions with internal motion (e.g. respiration in thorax and abdomen)

for ions: variations in radiological path length extremely important

Extension to moving targets

Target Motion Destroys Volume Conformity

time-dependent target positionfixed target position

3D online motion compensation (3D-OMC)

magnetic scanner system PMMA wedge system suitable motion tracking system

dynamic treatment plan

static moving, non-compensated

moving, compensated

real-time, highest precision

Summary:

Physical and technical properties

of proton and carbon beams

– Inverse depth dose profile

– Lateral scattering and dose gradients

– Intensity modulated beam delivery

– In vivo PET control of the beam

– Extension to moving targets

Thank you