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Range Verification Methods in Particle Therapy: Underlying Physics and Monte Carlo Modeling.

Kraan AC - Front Oncol (2015)

Bottom Line: Currently, uncertainties in particle range lead to the employment of safety margins, at the expense of treatment quality.We include research studies and clinically applied methods.For each of the techniques, we point out advantages and disadvantages, as well as clinical challenges still to be addressed, focusing on MC simulation aspects.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, National Institute for Nuclear Physics (INFN), University of Pisa , Pisa , Italy.

ABSTRACT
Hadron therapy allows for highly conformal dose distributions and better sparing of organs-at-risk, thanks to the characteristic dose deposition as function of depth. However, the quality of hadron therapy treatments is closely connected with the ability to predict and achieve a given beam range in the patient. Currently, uncertainties in particle range lead to the employment of safety margins, at the expense of treatment quality. Much research in particle therapy is therefore aimed at developing methods to verify the particle range in patients. Non-invasive in vivo monitoring of the particle range can be performed by detecting secondary radiation, emitted from the patient as a result of nuclear interactions of charged hadrons with tissue, including β (+) emitters, prompt photons, and charged fragments. The correctness of the dose delivery can be verified by comparing measured and pre-calculated distributions of the secondary particles. The reliability of Monte Carlo (MC) predictions is a key issue. Correctly modeling the production of secondaries is a non-trivial task, because it involves nuclear physics interactions at energies, where no rigorous theories exist to describe them. The goal of this review is to provide a comprehensive overview of various aspects in modeling the physics processes for range verification with secondary particles produced in proton, carbon, and heavier ion irradiation. We discuss electromagnetic and nuclear interactions of charged hadrons in matter, which is followed by a summary of some widely used MC codes in hadron therapy. Then, we describe selected examples of how these codes have been validated and used in three range verification techniques: PET, prompt gamma, and charged particle detection. We include research studies and clinically applied methods. For each of the techniques, we point out advantages and disadvantages, as well as clinical challenges still to be addressed, focusing on MC simulation aspects.

No MeSH data available.


Lateral scattering (FWHM – full width at half maximum) as function of distance from the beam exit window for various proton and carbon energies, calculated for a nozzle based on the GSI therapy facility. The beam enters the patient body at a distance of 1.40 m from the exit. Reproduced from Ref. (25), with permission.
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Figure 3: Lateral scattering (FWHM – full width at half maximum) as function of distance from the beam exit window for various proton and carbon energies, calculated for a nozzle based on the GSI therapy facility. The beam enters the patient body at a distance of 1.40 m from the exit. Reproduced from Ref. (25), with permission.

Mentions: Besides inelastic collisions with the atomic electrons, a charged particle also suffers numerous elastic Coulomb scatterings from the nuclei themselves. The energy loss as a result of multiple Coulomb scattering (MCS) is negligible, but it is nevertheless important for dosimetry, because it causes lateral broadening of the pencil beam. Theoretical calculations of the scattering angle are highly complex. One of the most complete derivations was performed by Molière (21), and various calculations in order to derive more practical formulas were performed afterwards, for instance by Lewis (22), Highland (23), and Gottschalk (24). Due to the Central Limit Theorem, the probability distribution of the net angle of deflection of a particle in a thick material is very nearly Gaussian, resulting from the sum of many small random deflections. An approximation for the probability distribution for the net angle of deflection by MCS in a material was derived by Highland (23), and can be approximated by a Gaussian distribution with a width given by:(7)θ0=14.1MeVβcpZpL/L0[1+0.038ln(L/L0)]where L the thickness of the scattering material and L0 the radiation length. The gaussian description is not perfect, and the presence of large-angle tails, which are the result of single scatters in the target, are not quite negligible and are typically simulated in MC codes. Also, for heavy particles, nuclear form factors should be applied, as well as Fano corrections (13). Figure 3 shows the lateral beam widening for proton and carbon projectiles.


Range Verification Methods in Particle Therapy: Underlying Physics and Monte Carlo Modeling.

Kraan AC - Front Oncol (2015)

Lateral scattering (FWHM – full width at half maximum) as function of distance from the beam exit window for various proton and carbon energies, calculated for a nozzle based on the GSI therapy facility. The beam enters the patient body at a distance of 1.40 m from the exit. Reproduced from Ref. (25), with permission.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4493660&req=5

Figure 3: Lateral scattering (FWHM – full width at half maximum) as function of distance from the beam exit window for various proton and carbon energies, calculated for a nozzle based on the GSI therapy facility. The beam enters the patient body at a distance of 1.40 m from the exit. Reproduced from Ref. (25), with permission.
Mentions: Besides inelastic collisions with the atomic electrons, a charged particle also suffers numerous elastic Coulomb scatterings from the nuclei themselves. The energy loss as a result of multiple Coulomb scattering (MCS) is negligible, but it is nevertheless important for dosimetry, because it causes lateral broadening of the pencil beam. Theoretical calculations of the scattering angle are highly complex. One of the most complete derivations was performed by Molière (21), and various calculations in order to derive more practical formulas were performed afterwards, for instance by Lewis (22), Highland (23), and Gottschalk (24). Due to the Central Limit Theorem, the probability distribution of the net angle of deflection of a particle in a thick material is very nearly Gaussian, resulting from the sum of many small random deflections. An approximation for the probability distribution for the net angle of deflection by MCS in a material was derived by Highland (23), and can be approximated by a Gaussian distribution with a width given by:(7)θ0=14.1MeVβcpZpL/L0[1+0.038ln(L/L0)]where L the thickness of the scattering material and L0 the radiation length. The gaussian description is not perfect, and the presence of large-angle tails, which are the result of single scatters in the target, are not quite negligible and are typically simulated in MC codes. Also, for heavy particles, nuclear form factors should be applied, as well as Fano corrections (13). Figure 3 shows the lateral beam widening for proton and carbon projectiles.

Bottom Line: Currently, uncertainties in particle range lead to the employment of safety margins, at the expense of treatment quality.We include research studies and clinically applied methods.For each of the techniques, we point out advantages and disadvantages, as well as clinical challenges still to be addressed, focusing on MC simulation aspects.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, National Institute for Nuclear Physics (INFN), University of Pisa , Pisa , Italy.

ABSTRACT
Hadron therapy allows for highly conformal dose distributions and better sparing of organs-at-risk, thanks to the characteristic dose deposition as function of depth. However, the quality of hadron therapy treatments is closely connected with the ability to predict and achieve a given beam range in the patient. Currently, uncertainties in particle range lead to the employment of safety margins, at the expense of treatment quality. Much research in particle therapy is therefore aimed at developing methods to verify the particle range in patients. Non-invasive in vivo monitoring of the particle range can be performed by detecting secondary radiation, emitted from the patient as a result of nuclear interactions of charged hadrons with tissue, including β (+) emitters, prompt photons, and charged fragments. The correctness of the dose delivery can be verified by comparing measured and pre-calculated distributions of the secondary particles. The reliability of Monte Carlo (MC) predictions is a key issue. Correctly modeling the production of secondaries is a non-trivial task, because it involves nuclear physics interactions at energies, where no rigorous theories exist to describe them. The goal of this review is to provide a comprehensive overview of various aspects in modeling the physics processes for range verification with secondary particles produced in proton, carbon, and heavier ion irradiation. We discuss electromagnetic and nuclear interactions of charged hadrons in matter, which is followed by a summary of some widely used MC codes in hadron therapy. Then, we describe selected examples of how these codes have been validated and used in three range verification techniques: PET, prompt gamma, and charged particle detection. We include research studies and clinically applied methods. For each of the techniques, we point out advantages and disadvantages, as well as clinical challenges still to be addressed, focusing on MC simulation aspects.

No MeSH data available.