title: Comparative Monte Carlo study on the performance of integration- and list-mode detector configurations for carbon ion computed tomography.
abstract: Ion beam therapy offers the possibility of a highly conformal tumor-dose distribution; however, this technique is extremely sensitive to inaccuracies in the treatment procedures. Ambiguities in the conversion of Hounsfield units of the treatment planning x-ray CT to relative stopping power (RSP) can cause uncertainties in the estimated ion range of up to several millimeters. Ion CT (iCT) represents a favorable solution allowing to directly assess the RSP. In this simulation study we investigate the performance of the integration-mode configuration for carbon iCT, in comparison with a single-particle approach under the same set-up. The experimental detector consists of a stack of 61 air-filled parallel-plate ionization chambers, interleaved with 3 mm thick PMMA absorbers. By means of Monte Carlo simulations, this design was applied to acquire iCTs of phantoms of tissue-equivalent materials. An optimization of the acquisition parameters was performed to reduce the dose exposure, and the implications of a reduced absorber thickness were assessed. In order to overcome limitations of integration-mode detection in the presence of lateral tissue heterogeneities a dedicated post-processing method using a linear decomposition of the detector signal was developed and its performance was compared to the list-mode acquisition. For the current set-up, the phantom dose could be reduced to below 30 mGy with only minor image quality degradation. By using the decomposition method a correct identification of the components and a RSP accuracy improvement of around 2.0% was obtained. The comparison of integration- and list-mode indicated a slightly better image quality of the latter, with an average median RSP error below 1.8% and 1.0%, respectively. With a decreased absorber thickness a reduced RSP error was observed. Overall, these findings support the potential of iCT for low dose RSP estimation, showing that integration-mode detectors with dedicated post-processing strategies can provide a RSP accuracy comparable to list-mode configurations.
authors.affiliation: Department of Medical Physics, Faculty of Physics, Ludwig-Maximilians-Universität München, Am Coulombwall 1, 85748 Garching b. München, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Meyer
authors.forename: Chiara
authors.initials: C
authors.lastname: Gianoli
authors.forename: Lorena
authors.initials: L
authors.lastname: Magallanes
authors.forename: Benedikt
authors.initials: B
authors.lastname: Kopp
authors.forename: Thomas
authors.initials: T
authors.lastname: Tessonnier
authors.forename: Guillaume
authors.initials: G
authors.lastname: Landry
authors.forename: George
authors.initials: G
authors.lastname: Dedes
authors.forename: Bernd
authors.initials: B
authors.lastname: Voss
authors.forename: Katia
authors.initials: K
authors.lastname: Parodi
mesh_terms: D063193:Heavy Ion Radiotherapy / Q000295:instrumentation / Q000379:methods* / Q000592:standards; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D000072232:Radiation Dosimeters / Q000592:standards; D011880:Radiotherapy Planning, Computer-Assisted / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*