title: Determination of the ion recombination correction factor for intraoperative electron beams.
abstract: The ion recombination correction factor (ks) is determined for the Advanced Markus chamber exposed to electron beams produced by a dedicated intraoperative radiation therapy (IORT) accelerator at medium dose-per-pulse values. The authors evaluate five different methods. Three of them are known as Boag's modified expressions, which are based on the two-voltage-analysis method and include the free-electron component. In the fourth method the IAEA TRS-398 protocol is applied, which uses the same two-voltage-analysis method but ignores the free-electron component, and finally the fifth approach is known as the Jaffé plot. ks values were obtained in the range of 4 mGy/pulse to 42 mGy/pulse and were compared with ks values determined by means of radiochromic films, which are independent of the dose rate. It was found that ks values that resulted from the three Boag's modified expressions and the TRS-398 protocol deviated by on average 1.5% and 1.4%, respectively, from the reference ks values based on film dosimetry. These results are within the estimated relative uncertainty of ±3%. On the other hand, the absolute deviation of each method depends on the dose-per-pulse value at which the method is investigated. In conclusion, in the medium dose-per-pulse range all Boag's modified expressions could be used for ks determination. Above a dose-per-pulse value of 35 mGy/pulse, the TRS-398 approach should be avoided. At 27 mGy/pulse and a maximum operation voltage of 300 V the ks value resulting from the Jaffé plot showed a 0.3% deviation from the reference value. More investigation on the Jaffé plot is necessary at higher dose-per-pulse values.
authors.affiliation: Department of Radiotherapy and Radiation Oncology, University Hospital of Duesseldorf, Germany; Faculty of Physics/Medical Physics, Heinrich-Heine University of Duesseldorf, Germany. Electronic address: majid.ghorbanpour@med.uni-duesseldorf.de.
authors.forename: Majid
authors.initials: M
authors.lastname: Ghorbanpour Besheli
authors.affiliation: Department of Radiotherapy and Radiation Oncology, University Hospital of Duesseldorf, Germany; Faculty of Physics/Medical Physics, Heinrich-Heine University of Duesseldorf, Germany.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Simiantonakis
authors.affiliation: Institute of Medical Physics and Radiation Protection (IMPS), University of Applied Science (THM) Gießen, Germany.
authors.forename: Klemens
authors.initials: K
authors.lastname: Zink
authors.affiliation: Department of Radiotherapy and Radiation Oncology, University Hospital of Duesseldorf, Germany.
authors.forename: Wilfried
authors.initials: W
authors.lastname: Budach
mesh_terms: D016477:Artifacts; D003198:Computer Simulation; D004583:Electrons / Q000627:therapeutic use; D006801:Humans; D007430:Intraoperative Care / Q000379:methods; D007477:Ions; D008954:Models, Biological; D009369:Neoplasms / Q000503:physiopathology* / Q000532:radiotherapy*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D018714:Radiotherapy, Adjuvant / Q000379:methods*; D011882:Radiotherapy, High-Energy / Q000379:methods*; D015203:Reproducibility of Results; D012542:Scattering, Radiation; D012680:Sensitivity and Specificity
chemical_list: D007477:Ions
keywords: Intraoperative Strahlentherapie; Intraoperative radiation therapy; Korrekturfaktor der Ionenrekombination; Two-Voltage-Analysis; Zweispannungsanalyse; free-electron fraction; freie Elektronen-Komponente; ion recombination correction factor