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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.


Measured positron emission activity together with the dose distribution for irradiation of a PMMA target with different projectiles: protons, 3He, 7Li, 12C, and 16O. Reproduced from Ref. (127), with permission.
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Figure 9: Measured positron emission activity together with the dose distribution for irradiation of a PMMA target with different projectiles: protons, 3He, 7Li, 12C, and 16O. Reproduced from Ref. (127), with permission.

Mentions: In Section 2, we have seen how nuclear reactions of incident protons and nuclei give rise to the production of β+ emitting fragments. By detecting the two 511 keV photons by positron annihilation, spatial distributions of the β+ decay points can be obtained. Often one-dimensional profiles along the beam-axis are chosen to display the activity along the beam path. In Figure 9, such profiles are displayed for various incident beam types impinging on a PMMA target. Normalization is arbitrary here. Two things can be noticed. First, the shape of the β+ activity profiles of light beams is remarkably different from those of heavier nuclei. While for the p, 3He, 7Li ion beams, the induced activity is only due to positron-emitting target residuals produced all along the beam path; for the 12C and 16O beams, there is an additional contribution in the activity from β+ emitting projectile residuals when they stop, near the end of range, explaining the activity peak. Second, we see that no direct correlation exists between β+-activity and the dose, which is not surprising, being based on different physics processes. Nevertheless, by comparing the measured PET data with reference distributions, it is possible to estimate whether the dose was delivered successfully. Large discrepancies between expected and measured PET data indicate problems in dose delivery. Such reference distributions are generally made with MC simulations on the basis of the treatment plan, time-course of irradiation, the patient CT, detector geometry, and imaging procedure (109). The application of PET to hadron therapy dose monitoring has been studied for about 20 years and is currently a well-established, although not widely used, method. Recent reviews can be found for instance in Ref. (4, 41).


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

Kraan AC - Front Oncol (2015)

Measured positron emission activity together with the dose distribution for irradiation of a PMMA target with different projectiles: protons, 3He, 7Li, 12C, and 16O. Reproduced from Ref. (127), with permission.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 9: Measured positron emission activity together with the dose distribution for irradiation of a PMMA target with different projectiles: protons, 3He, 7Li, 12C, and 16O. Reproduced from Ref. (127), with permission.
Mentions: In Section 2, we have seen how nuclear reactions of incident protons and nuclei give rise to the production of β+ emitting fragments. By detecting the two 511 keV photons by positron annihilation, spatial distributions of the β+ decay points can be obtained. Often one-dimensional profiles along the beam-axis are chosen to display the activity along the beam path. In Figure 9, such profiles are displayed for various incident beam types impinging on a PMMA target. Normalization is arbitrary here. Two things can be noticed. First, the shape of the β+ activity profiles of light beams is remarkably different from those of heavier nuclei. While for the p, 3He, 7Li ion beams, the induced activity is only due to positron-emitting target residuals produced all along the beam path; for the 12C and 16O beams, there is an additional contribution in the activity from β+ emitting projectile residuals when they stop, near the end of range, explaining the activity peak. Second, we see that no direct correlation exists between β+-activity and the dose, which is not surprising, being based on different physics processes. Nevertheless, by comparing the measured PET data with reference distributions, it is possible to estimate whether the dose was delivered successfully. Large discrepancies between expected and measured PET data indicate problems in dose delivery. Such reference distributions are generally made with MC simulations on the basis of the treatment plan, time-course of irradiation, the patient CT, detector geometry, and imaging procedure (109). The application of PET to hadron therapy dose monitoring has been studied for about 20 years and is currently a well-established, although not widely used, method. Recent reviews can be found for instance in Ref. (4, 41).

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.