| Zugriffsnummer | 46352 |
| Dokumenttyp | Konferenzartikel |
| Peer Review | unbekannt |
| Sprache | Englisch |
| Titel | KQ,B correction factors for ion chambers and the role of dead volumes |
| Autor(in); Institution |
Pojtinger, Stefan; 6.2, Dosimetrie für Strahlentherapie und Röntgendiagnostik, PTB-Braunschweig
Kapsch, Ralf-Peter; 6.2, Dosimetrie für Strahlentherapie und Röntgendiagnostik, PTB-Braunschweig
Thorwarth, Daniela; UKT, Tübingen, GERMANY
|
| Quelle/Jahr | Program and Abstracts - Virtual 8th MR in RT Symposium:(2021), S. 6 |
| Artikelnummer | 132 |
| URL | |
| Konferenzangaben | Virtual 8th MR in RT Symposium 2021, Virtual Conference, 18-21, April, 2021 |
| Freie Schlagworte | MR-guided radiotherapy ; reference dosimetry ; MR-linac ; magnetic field ; beam quality |
| Zusammenfassung | The response auf ionization chambers is altered in the presence of magnetic fields. As a consequence, the signal of a ionization chamber must be corrected by a magnetic field correction factor kQ,B, if the ionization chamber is used for absolute dosimetry in the presence of a magnetic field. This correction is mandatory for the determination of the absorbed dose to water at MR-linacs, where the magnetic field cannot be ramped down easily. The experimental determination of kQ,B is challenging, since experimental setups for this purpose are rare and, in addition, measurements of kQ,B at MR-linacs are mostly based on the use of radiation detectors which are usually not available at hospitals (e.g. calorimeters or alanine). An alternative option for the determination of kQ,B is by Monte-Carlo simulations, but it was shown in several publications, that the results of Monte Carlo simulations of ionization chambers in magnetic fields do not align with experimental results. Several authors have speculated, that this discrepancy could be explained by dead volumes that can be found close to the guard ring of ionization chambers. In this talk, several methods are presented for the determination of the magnetic field correction factors kQ,B. These include an experimental procedure in which measurements performed at a combination of a big electromagnet and a conventional linac are combined with measurements performed at a MR-linac. Another approach is presented, which is based on a cross-calibration with the chemical radiation detector alanine. In addition, a simulation method is presented, which can be used to include the dead volume of ionization chambers into Monte-Carlo simulations. |
