A review on reference dosimetry in radiation therapy with proton and light ion beams: status and impact of new developments

Vedelago, José; Karger, Christian P.; Jäkel, Oliver

doi:10.1016/j.radmeas.2022.106844

Cited by 13 publications

(10 citation statements)

References 117 publications

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“…However, reference dosimetry for proton beams in the presence of magnetic field has still to be thoroughly investigated, since it is required for quality assurance and safe application of radiation treatment. 22 This work studies the effect of various magnetic flux density from 0.1 to 1 Tesla on the response of Farmer-type ionization chambers with different inner radius. In addition, the magnetic field effect on the polarity and ion recombination correction factors, which are used for reference dosimetry, has been investigated.…”

Section: Introductionmentioning

confidence: 99%

“…Once technically feasible, MRgPT has a great potential for improving treatment of cancer therapy patients. However, reference dosimetry for proton beams in the presence of magnetic field has still to be thoroughly investigated, since it is required for quality assurance and safe application of radiation treatment 22 . This work studies the effect of various magnetic flux density from 0.1 to 1 Tesla on the response of Farmer‐type ionization chambers with different inner radius.…”

Section: Introductionmentioning

confidence: 99%

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Proton beam dosimetry in the presence of magnetic fields using Farmer‐type ionization chambers of different radii

et al. 2023

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Background Magnetic resonance‐guided proton therapy is promising, as it combines high‐contrast imaging of soft tissue with highly conformal dose delivery. However, proton dosimetry in magnetic fields using ionization chambers is challenging since the dose distribution as well as the detector response are perturbed. Purpose This work investigates the effect of the magnetic field on the ionization chamber response, and on the polarity and ion recombination correction factors, which are essential for the implementation of a proton beam dosimetry protocol in the presence of magnetic fields. Methods Three Farmer‐type cylindrical ionization chambers, the 30013 with 3 mm inner radius (PTW, Freiburg, Germany) and two custom built chambers “R1” and “R6” with 1 and 6 mm inner radii respectively were placed at the center of an experimental electromagnet (Schwarzbeck Mess – Elektronik, Germany) 2 cm depth of an in‐house developed 3D printed water phantom. The detector response was measured for a 3 × 10 cm2 field of mono‐energetic protons 221.05 MeV/u for the three chambers, and with an additional proton beam of 157.43 MeV/u for the chamber PTW 30013. The magnetic flux density was varied between 0.1 and 1.0 Tesla in steps of 0.1 Tesla. Results At both energies, the ionization chamber PTW 30013 showed a non‐linear response as a function of the magnetic field strength, with a decrease of the ionization chamber response of up to 0.27% ± 0.06% (1 SD) at 0.2 Tesla, followed by a smaller effect at higher magnetic field strength. For the chamber R1, the response decreased slightly with the magnetic field strength up to 0.45% ± 0.12% at 1 Tesla, and for the chamber R6, the response decreased up to 0.54% ± 0.13% at 0.1 Tesla, followed by a plateau up to 0.3 Tesla, and a weaker effect at higher magnetic field strength. The dependence of the polarity and recombination correction factor on the magnetic field was ⩽0.1% for the chamber PTW 30013. Conclusions The magnetic field has a small but significant effect on the chamber response in the low magnetic field region for the chamber PTW 30013 and for R6, and in the high magnetic field region for the chamber R1. Corrections may be necessary for ionization chamber measurements, depending on both the chamber volume and the magnetic flux density. No significant effect of the magnetic field on the polarity and recombination correction factor was detected in this work for the ionization chamber PTW 30013.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Proton beam dosimetry in the presence of magnetic fields using Farmer‐type ionization chambers of different radii

et al. 2023

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“…18 Since the higher order terms are in the order of 3 × 10 −5 , 18 the equal sign has been used. The depth dose curve of single spots (DAP w (z) in Equation 6) shall be measured with plane-parallel ICs with a large radius r to capture the off -axis, low-dose envelope, [20][21][22][23] that is r corresponds to x 0 , y 0 in Equation (5). Thus, the reciprocal approach of Equation ( 7) requires the application of fields with large widths 2x 0 and 2y 0 , which are measured along their central axis (D w,bf (0, 0, z)).…”

Section: Consistency Of the Energy Balancementioning

confidence: 99%

“…This changed to a = 1.131, b = -2.327 ⋅ 10 −5 and c = 2.046 ⋅ 10 −3 according to SOTA dosimetry protocols. 4,5 For the evaluation of D w,bf (0, 0, z), we set k NR,z = 1. The evaluated deviations from unity were considered in the uncertainty budget.…”

Section: B𝜌mentioning

confidence: 99%

“…Codes-of -practice recommend ionization chamber (IC) measurements for the reference dosimetry of clinical proton fields. [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%

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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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Dosimetric study for breathing‐induced motion effects in an abdominal pancreas phantom for carbon ion mini‐beam radiotherapy

Stengl,

Muñoz,

Arbes

et al. 2024

Medical Physics

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BackgroundParticle mini‐beam therapy exhibits promise in sparing healthy tissue through spatial fractionation, particularly notable for heavy ions, further enhancing the already favorable differential biological effectiveness at both target and entrance regions. However, breathing‐induced organ motion affects particle mini‐beam irradiation schemes since the organ displacements exceed the mini‐beam structure dimensions, decreasing the advantages of spatial fractionation.PurposeIn this study, the impact of breathing‐induced organ motion on the dose distribution was examined at the target and organs at risk(OARs) during carbon ion mini‐beam irradiation for pancreatic cancer.MethodsAs a first step, the carbon ion mini‐beam pattern was characterized with Monte Carlo simulations. To analyze the impact of breathing‐induced organ motion on the dose distribution of a virtual pancreas tumor as target and related OARs, the anthropomorphic Pancreas Phantom for Ion beam Therapy (PPIeT) was irradiated with carbon ions. A mini‐beam collimator was used to deliver a spatially fractionated dose distribution. During irradiation, varying breathing motion amplitudes were induced, ranging from 5 to 15 mm. Post‐irradiation, the 2D dose pattern was analyzed, focusing on the full width at half maximum (FWHM), center‐to‐center distance (ctc), and the peak‐to‐valley dose ratio (PVDR).ResultsThe mini‐beam pattern was visible within OARs, while in the virtual pancreas tumor a more homogeneous dose distribution was achieved. Applied motion affected the mini‐beam pattern within the kidney, one of the OARs, reducing the PVDR from 3.78 0.12 to 1.478 0.070 for the 15 mm motion amplitude. In the immobile OARs including the spine and the skin at the back, the PVDR did not change within 3.4% comparing reference and motion conditions.ConclusionsThis study provides an initial understanding of how breathing‐induced organ motion affects spatial fractionation during carbon ion irradiation, using an anthropomorphic phantom. A decrease in the PVDR was observed in the right kidney when breathing‐induced motion was applied, potentially increasing the risk of damage to OARs. Therefore, further studies are needed to explore the clinical viability of mini‐beam radiotherapy with carbon ions when irradiating abdominal regions.

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A review on reference dosimetry in radiation therapy with proton and light ion beams: status and impact of new developments

Cited by 13 publications

References 117 publications

Proton beam dosimetry in the presence of magnetic fields using Farmer‐type ionization chambers of different radii

Proton beam dosimetry in the presence of magnetic fields using Farmer‐type ionization chambers of different radii

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

Dosimetric study for breathing‐induced motion effects in an abdominal pancreas phantom for carbon ion mini‐beam radiotherapy

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