Beam monitor calibration of a synchrotron-based scanned light-ion beam delivery system

Osorio, J.; Dreindl, R.; Grevillot, L.; Letellier, V.; Kueß, Peter; Carlino, A.; Elia, Alessio

doi:10.1016/j.zemedi.2020.06.005

Cited by 15 publications

(27 citation statements)

References 19 publications

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“…). A detailed evaluation of the uncertainty budget resulting from both methods was conducted what resulted in a 1‐sigma standard deviation of 2.5% and 2.7% for the reference and redundant methods, respectively. The main factor responsible for the increase of the uncertainty budget of the redundant method is the inhomogeneity of the response of the Bragg peak chamber over its cross section.…”

Section: Key Resultsmentioning

confidence: 99%

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Clinical implementation and commissioning of the MedAustron Particle Therapy Accelerator for non‐isocentric scanned proton beam treatments

et al. 2019

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Purpose This paper describes the clinical implementation and medical commissioning of the MedAustron Particle Therapy Accelerator (MAPTA) for non‐isocentric scanned proton beam treatments. Methods Medical physics involvement during technical commissioning work is presented. Acceptance testing procedures, including advanced measurement methods of intra‐spill beam variations, are defined. Beam monitor calibration using two independent methods based on a dose‐area product formalism is described. Emphasis is given to the medical commissioning work and the specificities related to non‐isocentric irradiation, since a key feature of MedAustron is the routine delivery of non‐isocentric scanned proton beam treatments. Results Key commissioning results and beam stability trend lines for more than 2 yr of clinical operation have been provided. Intra‐spill beam range, size, and position variations were within specifications of 0.3 mm, 15%, and 0.5 mm, respectively. The agreement between two independent beam monitor calibration methods was better than 1.0%. Non‐isocentric treatment delivery allowed lateral penumbra reduction of up to about 30%. Daily QA measurements of the beam range, size, position, and dose were always within 1 mm, 10%, 1 mm, and 2% from the baseline data, respectively. Conclusions Non‐isocentric treatments have been successfully implemented at MedAustron for routine scanned proton beam therapy using horizontal and vertical fixed beamlines. Up to now every patient was treated in non‐isocentric conditions. The presented methodology to implement a new Scanned Ion Beam Delivery (SIBD) system into clinical routine for proton therapy may serve as a guidance for other centers.

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Section: Key Resultsmentioning

confidence: 99%

“…The beam monitors were calibrated in terms of number of particles (N) per monitor unit (MU) in reference conditions using two methods . The first method considered as reference is based on the procedure proposed in Ref.…”

Section: Methodsmentioning

confidence: 99%

Clinical implementation and commissioning of the MedAustron Particle Therapy Accelerator for non‐isocentric scanned proton beam treatments

et al. 2019

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“…For scanned beams, however, the beam monitor has to be calibrated for each energy layer in terms of absorbed dose at shallow depth and it has been demonstrated that the same formalism and data can be used (for a review of the literature on this subject, see Palmans and Vatnitsky, 2016 [43]. This is also the approach used for reference dosimetry at MedAustron [45].…”

Section: Data Evaluation and Statistical Testingmentioning

confidence: 99%

MR‐guided proton therapy: Impact of magnetic fields on the detector response

et al. 2021

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Purpose: To investigate the response of detectors for proton dosimetry in the presence of magnetic fields. Material&Methods: Four ionization chambers, two thimble-type and two plane-parallel-type, and a diamond detector were investigated. All detectors were irradiated with homogeneous single-energy-layer fields, using 252.7 MeV proton beams. A Farmer ionization chamber was additionally irradiated in the same geometrical configuration, but with a lower nominal energy of 97.4 MeV. The beams were subjected to magnetic field strengths of 0, 0.25, 0.5, 0.75 and 1 T produced by a research dipole magnet placed at the room's isocenter. Detectors were positioned at 2 cm water-equivalent depth, with their stem perpendicular to both the magnetic field lines and the proton beam's central axis, in the direction of the Lorentz force. Normality and two sample statistical Student's t-tests were performed to assess the influence of the magnetic field on the detectors' responses. Results: For all detectors, a small but significant magnetic-field-dependent change of their response was found. Observed differences compared to the no magnetic field case ranged from +0.5% to-0.7%. The magnetic field dependence was found to be non-linear and highest between 0.25 and 0.5 T for 252.7 MeV proton beams. A different variation of the Farmer chamber response with magnetic field strength was observed for irradiations using lower energy (97.4 MeV) protons. The largest magnetic field effects were observed for plane-parallel ionization chambers. Conclusion: Small magnetic-field-dependent changes in the detector response were identified, which should be corrected for dosimetric applications.

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“…For scanned proton beams, reference dosimetry is mostly based on the determination of absorbed dose to water at shallow depth in single-layer fields, a method first proposed for carbon ion beams 3,4 and later implemented for protons. [5][6][7][8] A single-layer field constitutes of a single nominal-energy beam covering a certain lateral area with equal-energy spots that are equidistant in both orthogonal directions and in which the same number of particles is delivered per spot. An alternative method using a largearea plane-parallel ionization chamber has also been proposed but has not been as well established.…”

Section: Introductionmentioning

confidence: 99%

“…For the single-layer method, it has been proposed that a Farmer-type ionization chamber (IC) or a plane-parallel ionization chamber (PPIC) can be used for the determination of absorbed dose to water in reference conditions. 5,8,10 Since for most of the clinical proton beam energy range, there are depth dose gradients present at shallow depths, preference may be given to the use of a PPIC. However, there remain indications that the beam quality correction factors for PPIC are not as unique for a given chamber type as they are for most Farmer-type ICs and the long-term stability of commercial PPICs has been shown to be inferior to those of Farmertype ICs.…”

Section: Introductionmentioning

confidence: 99%

Gradient corrections for reference dosimetry using Farmer‐type ionization chambers in single‐layer scanned proton fields

Medin

Trnková

2020

Medical Physics

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Purpose The local depth dose gradient and the displacement correction factor for Farmer‐type ionization chambers are quantified for reference dosimetry at shallow depth in single‐layer scanned proton fields. Method Integrated radial profiles as a function of depth (IRPDs) measured at three proton therapy centers were smoothed by polynomial fits. The local relative depth dose gradient at measurement depths from 1 to 5 cm were derived from the derivatives of those fits. To calculate displacement correction factors, the best estimate of the effective point of measurement was derived from reviewing experimental and theoretical determinations reported in the literature. Displacement correction factors for the use of Farmer‐type ionization chambers with their reference point (at the center of the cavity volume) positioned at the measurement depth were derived as a ratio of IRPD values at the measurement depth and at the effective point of measurement. Results Depth dose gradients are as low as 0.1–0.4% per mm at measurement depths from 1 to 5 cm in the highest clinical proton energies (with residual ranges higher than 15 cm) and increase to 1% per mm at a residual range of 4 cm and become larger than 3% per mm for residual ranges lower than 2 cm. The literature review shows that the effective point of measurement of Farmer‐type ionization chambers is, similarly as for carbon ion beams, located 0.75 times the cavity radius closer to the beam origin as the center of the cavity. If a maximum displacement correction of 2% is deemed acceptable to be included in calculated beam quality correction factors, Farmer‐type ICs can be used at measurements depths from 1 to 5 cm for which the residual range is 4 cm or larger. If one wants to use the same beam quality correction factors as applicable to the conventional measurement point for scattered beams, located at the center of the SOBP, the relative standard uncertainty on the assumption that the displacement correction factor is unity can be kept below 0.5% for measurement depths of at least 2 cm and for residual ranges of 15 cm or higher. Conclusion The literature review confirmed that for proton beams the effective point of measurement of Farmer‐type ionization chambers is located 0.75 times the cavity radius closer to the beam origin as the center of the cavity. Based on the findings in this work, three options can be recommended for reference dosimetry of scanned proton beams using Farmer‐type ionization chambers: (a) positioning the effective point of measurement at the measurement depth, (b) positioning the reference point at the measurement depth and applying a displacement correction factor, and (c) positioning the reference point at the measurement depth without applying a displacement correction factor. Based on limiting the acceptable uncertainty on the gradient correction factor to 0.5% and the maximum deviation of the displacement perturbation correction factor from unity to 2%, the first two options can be allowed for residual ranges of at least 4 cm while the thi...

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Beam monitor calibration of a synchrotron-based scanned light-ion beam delivery system

Cited by 15 publications

References 19 publications

Clinical implementation and commissioning of the MedAustron Particle Therapy Accelerator for non‐isocentric scanned proton beam treatments

Clinical implementation and commissioning of the MedAustron Particle Therapy Accelerator for non‐isocentric scanned proton beam treatments

MR‐guided proton therapy: Impact of magnetic fields on the detector response

Gradient corrections for reference dosimetry using Farmer‐type ionization chambers in single‐layer scanned proton fields

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