Protocol for Heavy Charged-Particle Therapy Beam Dosimetry

Lyman, John; Awschalom, M.; Berardo, Peter A.; Bicchsel, Hans; Chen, George T.Y.; Dicello, J. F.; Fessenden, Peter; Goitein, Michael; Lam, Gabriel K. Y.; McDonald, Joseph C.; Smith, Alfred Ft.; Haken, R. Ten; Verhey, Lynn; Zink, Sandra

doi:10.37206/15

Cited by 21 publications

(3 citation statements)

References 55 publications

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“…Except at low velocities, the heavy charged particles lose a negligible amount of energy in nuclear collisions. Also, heavy charged particles colliding with electrons will lose only a small fraction of their energy per collision (usually about 25 eV, but on the average 100 eV and at most >> 4 mE/M) [ 19 ]. Thus, the heavy particles have much larger relative dose in the Bragg peak and small lateral scattering than protons and they offer an improved dose conformation as compared with photon and proton beam.…”

Section: Interactions Of Particles With Mattermentioning

confidence: 99%

Basics of particle therapy I: physics

Park

Kang

2011

Radiat Oncol J

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With the advance of modern radiation therapy technique, radiation dose conformation and dose distribution have improved dramatically. However, the progress does not completely fulfill the goal of cancer treatment such as improved local control or survival. The discordances with the clinical results are from the biophysical nature of photon, which is the main source of radiation therapy in current field, with the lower linear energy transfer to the target. As part of a natural progression, there recently has been a resurgence of interest in particle therapy, specifically using heavy charged particles, because these kinds of radiations serve theoretical advantages in both biological and physical aspects. The Korean government is to set up a heavy charged particle facility in Korea Institute of Radiological & Medical Sciences. This review introduces some of the elementary physics of the various particles for the sake of Korean radiation oncologists' interest.

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Section: Interactions Of Particles With Mattermentioning

confidence: 99%

Basics of particle therapy I: physics

Park

Kang

2011

Radiat Oncol J

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“…[1][2][3][4][5] In principle, fluence measurements with Faraday cups (FCs) form a promising alternative. This was initially recommended in the AAPM TG 16 protocol 6 and is even more desirable due to the following recent developments:…”

Section: Introductionmentioning

confidence: 99%

“…In principle, fluence measurements with Faraday cups (FCs) form a promising alternative. This was initially recommended in the AAPM TG 16 protocol 6 and is even more desirable due to the following recent developments: Treatment heads designed specifically for pencil‐beam scanning (PBS) delivery, often feature laterally small, isolated beamlets ('spots'). As these can be captured by FCs with a high geometric detection efficiency, the experimental conditions are well defined. The dose computation modules of treatment planning systems and dose engines for an independent validation employ the Monte‐Carlo (MC) simulation method, which in turn contains the proton fluence

\Phi _\mathrm{p}

normalized to the monitor unit (MU) in the source model. FCs are inherently independent of the incident fluence rate of primary protons.…”

Section: Introductionmentioning

confidence: 99%

Consistency of Faraday cup and ionization chamber dosimetry of proton fields and the role of nuclear interactions

Wulff,

Paul,

Bäcker

et al. 2023

Medical Physics

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BackgroundA Faraday cup (FC) facilitates a quite clean measurement of the proton fluence emerging from clinical spot‐scanning nozzles with narrow pencil‐beams. The utilization of FCs appears to be an attractive option for high dose rate delivery modes and the source models of Monte‐Carlo (MC) dose engines. However, previous studies revealed discrepancies of 3%–6% between reference dosimetry with ionization chambers (ICs) and FC‐based dosimetry. This has prevented the widespread use of FCs for dosimetry in proton therapy.PurposeThe current study aims at bridging the gap between FC dosimetry and IC dosimetry of proton fields delivered with spot‐scanning treatment heads. Particularly, a novel method to evaluate FC measurements is introduced.MethodsA consistency check is formulated, which makes use of the energy balance and the reciprocity theorem. The measurement data comprise central‐axis depth distributions of the absorbed dose of quasi‐monochromatic fields with a width of about 28.5 cm and FC measurements of the reciprocal fields with a single spot. These data are complemented by a look‐up of energy‐range tables, the average Q‐value of transmutations, and the escape energy carried away by neutrons and photons. The latter data are computed by MC simulations, which in turn are validated with measurements of the distal dose tail and neutron out‐of‐field doses. For comparison, the conventional approach of FC evaluation is performed, which computes absorbed dose from the product of fluence and stopping power. The results from the FC measurements are compared with the standard dosimetry protocols and improved reference dosimetry methods.ResultsThe deviation between the conventional FC‐based dosimetry and the IC‐based one according to standard dosimetry protocols was −4.7 (± 3.3)% for a 100 MeV field and −3.6 (±3.5)% for 200 MeV, thereby agreeing within the reported uncertainties. The deviations could be reduced to −4.0 (± 2.9)% and −3.0 (± 3.1)% by adopting state‐of‐the‐art reference dosimetry methods. The alternative approach using the energy balance gave deviations of only −1.9% (100 MeV) and −2.6% (200 MeV) using state‐of‐the‐art dosimetry. The standard uncertainty of this novel approach was estimated to be about 2%.ConclusionsAn alternative concept has been established to determine the absorbed dose of monoenergetic proton fields with an FC. It eliminates the strong dependence of the conventional FC‐based approach on the MC simulation of the stopping‐power and of the secondary ions, which according to the study at hand is the major contributor to the underestimation of the absorbed dose. Some contributions to the uncertainty of the novel approach could potentially be reduced in future studies. This would allow for accurate consistency tests of conventional dosimetry procedures.

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Characterization of a high‐resolution 2D transmission ion chamber for independent validation of proton pencil beam scanning of conventional and FLASH dose delivery

et al. 2021

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Introduction: Ultra-high dose rate (FLASH) radiotherapy has become a popular research topic with the potential to reduce normal tissue toxicities without losing the benefit of tumor control. The development of FLASH proton pencil beam scanning (PBS) delivery requires accurate dosimetry despite high beam currents with correspondingly high ionization densities in the monitoring chamber. In this study, we characterized a newly designed high-resolution position sensing transmission ionization chamber with a purpose-built multichannel electrometer for both conventional and FLASH dose rate proton radiotherapy. Methods: The dosimetry and positioning accuracies of the ion chamber were fully characterized with a clinical scanning beam. On the FLASH proton beamline, the cyclotron output current reached up to 350 nA with a maximum energy of 226.2 MeV, with 210 AE 3 nA nozzle pencil beam current. The ion recombination effect was characterized under various bias voltages up to 1000 V and different beam intensities. The charge collected by the transmission ion chamber was compared with the measurements from a Faraday cup. Results: Cross-calibrated with an Advanced Markus chamber (PTW, Freiburg, Germany) in a uniform PBS proton beam field at clinical beam setting, the ion chamber calibration was 38.0 and 36.7 GyEÁmm 2 /nC at 100 and 226.2 MeV, respectively. The ion recombination effect increased with larger cyclotron current at lower bias voltage while remaining ≤0.5 AE 0.5% with ≥200 V of bias voltage. Above 200 V, the normalized ion chamber readings demonstrated good linearity with the mass stopping power in air for both clinical and FLASH beam intensities. The spot positioning accuracy was measured to be 0.10 AE 0.08 mm in two orthogonal directions. Conclusion:We characterized a transmission ion chamber system under both conventional and FLASH beam current densities and demonstrated its suitability for use as a proton pencil beam dose and spot position delivery monitor under FLASH dose rate conditions.

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Protocol for Heavy Charged-Particle Therapy Beam Dosimetry

Cited by 21 publications

References 55 publications

Basics of particle therapy I: physics

Basics of particle therapy I: physics

Consistency of Faraday cup and ionization chamber dosimetry of proton fields and the role of nuclear interactions

Characterization of a high‐resolution 2D transmission ion chamber for independent validation of proton pencil beam scanning of conventional and FLASH dose delivery

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