title: Patient specific optimization of the relation between CT-hounsfield units and proton stopping power with proton radiography.
abstract: The purpose of this work is to show the feasibility of using in vivo proton radiography of a radiotherapy patient for the patient individual optimization of the calibration from CT-Hounsfield units to relative proton stopping power. Water equivalent tissue (WET) calibrated proton radiographs of a dog patient treated for a nasal tumor were used as baseline in comparison with integrated proton stopping power through the calibrated CT of the dog. In an optimization procedure starting with a stoichiometric calibration curve, the calibration was modified randomly. The result of this iteration is an optimized calibration curve which was used to recalculate the dose distribution of the patient. One result of this experiment was that the mean value of the deviations between WET calculations based on the stoichiometric calibration curve and the measurements was shifted systematically away from zero. The calibration produced by the optimization procedure reduced this shift to around 0.4 mm. Another result was that the precision of the calibration, reflected as the standard deviation of the normally distributed deviations between WET calculation and measurement, could be reduced from 7.9 to 6.7 mm with the optimized calibration. The dose distributions based on the two calibration curves showed major deviations at the distal end of the target volume.
authors.affiliation: Department of Radiation Oncology and Nuclear Medicine, City Hospital Triemli, 8063 Zürich, Switzerland. uwe.schneider@psi.ch
authors.forename: Uwe
authors.initials: U
authors.lastname: Schneider
authors.forename: Peter
authors.initials: P
authors.lastname: Pemler
authors.forename: Jürgen
authors.initials: J
authors.lastname: Besserer
authors.forename: Eros
authors.initials: E
authors.lastname: Pedroni
authors.forename: Antony
authors.initials: A
authors.lastname: Lomax
authors.forename: Barbara
authors.initials: B
authors.lastname: Kaser-Hotz
mesh_terms: D000818:Animals; D002138:Calibration; D004285:Dogs; D006801:Humans; D009303:Nasopharyngeal Neoplasms / Q000532:radiotherapy*; D019047:Phantoms, Imaging; D011522:Protons; D011859:Radiography; D011874:Radiometry; D011878:Radiotherapy / Q000379:methods*; D011879:Radiotherapy Dosage; D011880:Radiotherapy Planning, Computer-Assisted; D013679:Technology, Radiologic; D014057:Tomography, X-Ray Computed / Q000379:methods*
chemical_list: D011522:Protons