Optimal orientation for ionization chambers in MRgRT reference dosimetry

Pojtinger, Stefan; Dohm, O.; Thorwarth, Daniela

doi:10.1515/cdbme-2017-0056

Cited by 1 publication

(2 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The results clearly showed that the magnetic field correction factor

k_{B,Q}

strongly depends on the chamber volume and the chamber orientation with respect to the beam and magnetic field directions. The smallest deviation of

k_{B,Q}

from unity occurs in case when the magnetic field is directed parallel to the chamber axis 3,5,11,24–26 . In that case, the correction factor is below 1.2% for the 0.6 cm 3 SNC600c and below 0.4% for the small SNC125c chamber, even for a

\vec{B}

‐field strength of 1.5 T, which is the maximum magnetic field strength of commercially available MRI‐linacs.…”

Section: Discussionmentioning

confidence: 99%

“…The smallest deviation of k B,Q from unity occurs in case when the magnetic field is directed parallel to the chamber axis. 3,5,11,[24][25][26] In that case, the correction factor is below 1.2% for the 0.6 cm 3 SNC600c and below 0.4% for the small SNC125c chamber, even for a ⃗ B-field strength of 1.5 T, which is the maximum magnetic field strength of commercially available MRI-linacs.…”

Section: Discussionmentioning

confidence: 99%

See 1 more Smart Citation

Experimental and Monte Carlo‐based determination of magnetic field correction factors kB,Q$k_{B,Q}$ in high‐energy photon fields for two ionization chambers

et al. 2023

View full text Add to dashboard Cite

Background: The integration of magnetic resonance tomography into clinical linear accelerators provides high-contrast, real-time imaging during treatment and facilitates online-adaptive workflows in radiation therapy treatments. The associated magnetic field also bends the trajectories of charged particles via the Lorentz force, which may alter the dose distribution in a patient or a phantom and affects the dose response of dosimetry detectors. Purpose: To perform an experimental and Monte Carlo-based determination of correction factors k B,Q , which correct the response of ion chambers in the presence of external magnetic fields in high-energy photon fields. Methods: The response variation of two different types of ion chambers (Sun Nuclear SNC125c and SNC600c) in strong external magnetic fields was investigated experimentally and by Monte Carlo simulations. The experimental data were acquired at the German National Metrology Institute, PTB, using a clinical linear accelerator with a nominal photon energy of 6 MV and an external electromagnet capable of generating magnetic flux densities of up to 1.5 T in opposite directions. The Monte Carlo simulation geometries corresponded to the experimental setup and additionally to the reference conditions of IAEA TRS-398. For the latter, the Monte Carlo simulations were performed with two different photon spectra: the 6 MV spectrum of the linear accelerator used for the experimental data acquisition and a 7 MV spectrum of a commercial MRI-linear accelerator. In each simulation geometry, three different orientations of the external magnetic field, the beam direction and the chamber orientation were investigated. Results: Good agreement was achieved between Monte Carlo simulations and measurements with the SNC125c and SNC600c ionization chambers, with a mean deviation of 0.3% and 0.6%, respectively. The magnitude of the correction factor k B,Q strongly depends on the chamber volume and on the orientation of the chamber axis relative to the external magnetic field and the beam directions.It is greater for the SNC600c chamber with a volume of 0.6 cm 3 than for the SNC125c chamber with a volume of 0.1 cm 3 . When the magnetic field direction and the chamber axis coincide, and they are perpendicular to the beam direction, the ion chambers exhibit a calculated overresponse of less than 0.7(6)% (SNC600c) and 0.3(4)% (SNC125c) at 1.5 T and less than 0.3(0)% (SNC600c) and 0.1(3)% (SNC125c) for 0.35 T for nominal beam energies of 6 MV and 7 MV. This chamber orientation should be preferred, as k B,Q may increase significantlyThis is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

show abstract

“…The results clearly showed that the magnetic field correction factor