title: Photoelectric-enhanced radiation therapy with quasi-monochromatic computed tomography.
abstract: Photoelectric-enhanced radiation therapy is a bimodal therapy, consisting of the administration of highly radiation-absorbing substances into the tumor area and localized regional irradiation with orthovoltage x-rays. Irradiation can be performed by a modified computed tomography (CT) unit equipped with an additional x-ray optical module which converts the polychromatic, fan-shaped CT beam into a monochromatized and focused beam for energy-tuned photoelectric-enhanced radiotherapy. A dedicated x-ray optical module designed for spatial collimation, focusing, and monochromatization was mounted at the exit of the x-ray tube of a clinical CT unit. Spectrally resolved measurements of the resulting beam were performed using an energy-dispersive detection system calibrated by synchrotron radiation. The spatial photon fluence was determined by film dosimetry. Depth-dose measurements were performed and compared to the polychromatic CT and a therapeutic 6 MV beam. The spatial dose distribution in phantoms using a rotating radiation source (quasimonochromatic CT and 6 MV, respectively) was investigated by gel dosimetry. The photoelectric dose enhancement for an iodine fraction of 1% in tissue was calculated and verified experimentally. The x-ray optical module selectively filters the energy of the tungsten Kalpha emission line with an FWHM of 5 keV. The relative photon fluence distribution demonstrates the focusing characteristic of the x-ray optical module. A beam width of about 3 mm was determined at the isocenter of the CT gantry. The depth-dose measurements resulted in a half-depth value of approximately 36 mm for the CT beams (quasi-monochromatic, polychromatic) compared to 154 mm for the 6 MV beam. The rotation of the radiation source leads to a steep dose gradient at the center of rotation; the gel dosimetry yields an entrance-to-peak dose ratio of 1:10.8 for the quasi-monochromatic CT and 1:37.3 for a 6 MV beam of the same size. The photoelectric dose enhancement factor increases from 2.2 to 2.4 by using quasi-monochromatic instead of polychromatic radiation. An additional increase in the radiation dose by a factor of 1.4 due to the focusing characteristic of the x-ray optical module was calculated. Photoelectric-enhanced radiation therapy based on a clinical CT unit combined with an x-ray optical module is a novel therapy option in radiation oncology. The optimized quasi-monochromatic radiation is strongly focused and ensures high photoelectric dose enhancement for iodine.
authors.affiliation: TRG Diagnostic Imaging, Bayer Schering Pharma AG, 13353 Berlin, Germany. gregor.jost@bayerhealthcare.com
authors.forename: Gregor
authors.initials: G
authors.lastname: Jost
authors.forename: Tristan
authors.initials: T
authors.lastname: Mensing
authors.forename: Sven
authors.initials: S
authors.lastname: Golfier
authors.forename: Rüdiger
authors.initials: R
authors.lastname: Lawaczeck
authors.forename: Hubertus
authors.initials: H
authors.lastname: Pietsch
authors.forename: Joachim
authors.initials: J
authors.lastname: Hütter
authors.forename: Levent
authors.initials: L
authors.lastname: Cibik
authors.forename: Martin
authors.initials: M
authors.lastname: Gerlach
authors.forename: Michael
authors.initials: M
authors.lastname: Krumrey
authors.forename: Daniel
authors.initials: D
authors.lastname: Fratzscher
authors.forename: Vladimir
authors.initials: V
authors.lastname: Arkadiev
authors.forename: Reiner
authors.initials: R
authors.lastname: Wedell
authors.forename: Michael
authors.initials: M
authors.lastname: Haschke
authors.forename: Norbert
authors.initials: N
authors.lastname: Langhoff
authors.forename: Peter
authors.initials: P
authors.lastname: Wust
authors.forename: Lutz
authors.initials: L
authors.lastname: Lüdemann
mesh_terms: D017076:Computer-Aided Design; D004867:Equipment Design; D019544:Equipment Failure Analysis; D020266:Radiotherapy, Conformal / Q000295:instrumentation*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D014057:Tomography, X-Ray Computed / Q000295:instrumentation*