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Proton and ion beams therapy

The first cancer treatment with a proton beam was carried out about 70 years ago.

During these decades the clinical use of proton and ion beams for cancer treatment has improved a lot as you can see from the spread of the treatment centers and from the big amount of scientific publication about this topic. ��Unlike electrons, protons allow a high dose deposition in a small deep-seated space; that causes a major precision on irradiating the target and less damage of surrounding and healthy tissues.

From the first time more than 160,000 people are been treated with protons worldwide.

The CATANA (Centro di AdroTerapia ed Applicazioni Nucleari Avanzate) facility, at LNS-INFN in Catania, started its activity on 2002 and more than 300 patients have been treated there until now.

references: [1], [2]

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Radiobiological quantities

DOSE [Gy]

the energy deposited by ionizing radiation per unit mass.

RBE

The Relative Biological Effectiveness is the ratio between the dose of a standard radiation that produces a certain biological damage and the dose of the test radiation needed to produce the same damage

LET [keV/μm]

The Linear Energy Transfer is a measure of the energy transferred to the matter by an ionising particle.

references: [3], [4]

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GEANT4

GEANT4 is a software toolkit for the simulation of the passage of particles through matter. It is written in C++ and exploits advanced software-engineering techniques and object-oriented technology.

It is used in different application fields:

high energy physics
astrophysics
medical physics

space science
radiation protection

references: [5]

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All aspects of the simulation process have been included in the toolkit:

the geometry of the system,
the materials involved,
the fundamental particles of interest,
the generation of primary events,
the tracking of particles through materials and electromagnetic fields,
the physics processes governing particle interactions,
the response of sensitive detector components,
the generation of event data,
the storage of events and tracks,
the visualization of the detector and particle trajectories,
the capture and analysis of simulation data at different levels of detail and refinement.

references: [5]

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The advanced example: “Hadrontherapy”

references: [1], [4]

Handrontherapy is a free and open source Monte Carlo application. It uses the libraries of the Geant4 simulation toolkit and it is included in the advanced examples.�The geometry is divided in two main blocks: one consists in the geometry of a typical beam line for proton/ion therapy, another is the detection region.�All the transport elements are included.

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CATANA

View of the CATANA beam line: 1. treatment chair for patient immobilization; 2. final collimator; 3. positioning laser; 4. light field simulator; 5. monitor chambers; 6. intermediate collimator; 7. box for the location of modulator wheel and range shifter.

The CATANA facility is in Catania at INFN - LNS. It is a passive proton beam line (shown in the figure).

The proton beam go through two scattering foils made of tantalum: the first one is 15 μm thick and it’s placed in vacuum before the beam exits in air; the second one is 25 μm thick and it has a central brass stopper with a diameter of 4 mm.

references: [6]

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The scattering system is designed to obtain a homogenous lateral off-axis dose distribution and to minimize the energy loss.

The exit window is made of 50 μm kapton and it is about 3 meters far from isocenter.

Inside a box placed downstream of the second scattering foil, there are a range shifter and a range modulator.

The facility is provided with two transmission monitor ionization chamber to obtain an on-line control of the dose delivered. A light field allows to simulate the radiation field.

The isocenter identification and the patient centering are obtained by using two diode lasers: one is orthogonal to beam line and the other is coaxial to beam line. Before isocenter (83 mm upstream) there is a brass shaped patient collimator.

references: [6]

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A new example: “The Extended Example”

The new application enable the user to simulate, in a simple way, the effects of radiation on a detector region (a parallelepiped).

The classes Dose, LET and RBE allow to obtain these quantities as outputs. An interesting characteristic of the example is the presence of the class Radiobiomanager that makes easy adding new classes in the code to implement the calculation of others radiobiological quantities.

The particle source can be customized by using the Primary Generator Action.

The utilization is straightforward for an inexpert user because of the simplicity of geometry and of the code.

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LET dose total and LET track total

N = number of a certain type of ion ; n = number of different type of ion

Also, in both examples, it is possible obtaining as output the contribute of the different type of ions.

references: [7]

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RBE

Input --> tables that contain data about cellular lines and different incident ions:

α and β values in function of kinetic energies of particles
values Dcut , αx and βx that depends on the cell type

The code interpolates for each particles and find αi and βi

Than calculates and (mean values for each slice)

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RBE and Survival Fraction can be calculated:

if D ≤ Dcut

if D > Dcut

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Comparison between Hadrontherapy and Extended Example

Source: 60 MeV protons
Phantom: 4x4x4 cm3
Voxel 0.1 mm (x direction)
n. of particles 1000000
Physics: Hadrontherapy_1
Material: G4_WATER

macro Hadrontherapy

macro Extended Example

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Dose, LETD and LETT

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Comparison between Hadrontherapy and Extended Example

Source: 150 MeV protons
Phantom: 20x20x20 cm3
Voxel 0.1 mm (x direction)
n. of particles 1000000
Physics: Hadrontherapy_1
Material: G4_WATER

macro Hadrontherapy

macro Extended Example

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Dose, LETD and LETT

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Comparison between Hadrontherapy and Extended Example

Source: 62 MeV protons
Phantom: 4x4x4 cm3
Voxel 0.1 mm (x direction)
n. of particles 1000000
Physics: Hadrontherapy_1
Material: G4_WATER
Table used for RBE:

Lem1_ARPE19

macro Hadrontherapy

macro Extended Example

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Comparison between Hadrontherapy and Extended Example

Source: 62 MeV protons
Phantom: 4x4x4 cm3
Voxel 0.1 mm (x direction)
n. of particles 1000000
Physics: Hadrontherapy_1
Material: G4_WATER
Table used for RBE:

Lem2_ARPE19

macro Hadrontherapy

macro Extended Example

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