title: Converging stereotactic radiotherapy using kilovoltage X-rays: experimental irradiation of normal rabbit lung and dose-volume analysis with Monte Carlo simulation.
abstract: OBJECTIVE
  To validate the feasibility of developing a radiotherapy unit with kilovoltage X-rays through actual irradiation of live rabbit lungs, and to explore the practical issues anticipated in future clinical application to humans through Monte Carlo dose simulation.
  
  
  METHODS
  A converging stereotactic irradiation unit was developed, consisting of a modified diagnostic computed tomography (CT) scanner. A tiny cylindrical volume in 13 normal rabbit lungs was individually irradiated with single fractional absorbed doses of 15, 30, 45, and 60 Gy. Observational CT scanning of the whole lung was performed every 2 weeks for 30 weeks after irradiation. After 30 weeks, histopathologic specimens of the lungs were examined. Dose distribution was simulated using the Monte Carlo method, and dose-volume histograms were calculated according to the data. A trial estimation of the effect of respiratory movement on dose distribution was made.
  
  
  RESULTS
  A localized hypodense change and subsequent reticular opacity around the planning target volume (PTV) were observed in CT images of rabbit lungs. Dose-volume histograms of the PTVs and organs at risk showed a focused dose distribution to the target and sufficient dose lowering in the organs at risk. Our estimate of the dose distribution, taking respiratory movement into account, revealed dose reduction in the PTV.
  
  
  CONCLUSIONS
  A converging stereotactic irradiation unit using kilovoltage X-rays was able to generate a focused radiobiologic reaction in rabbit lungs. Dose-volume histogram analysis and estimated sagittal dose distribution, considering respiratory movement, clarified the characteristics of the irradiation received from this type of unit.
authors.affiliation: Department of Radiology, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Takatsugu
authors.initials: T
authors.lastname: Kawase
authors.forename: Etsuo
authors.initials: E
authors.lastname: Kunieda
authors.forename: Hossain M
authors.initials: HM
authors.lastname: Deloar
authors.forename: Takanori
authors.initials: T
authors.lastname: Tsunoo
authors.forename: Satoshi
authors.initials: S
authors.lastname: Seki
authors.forename: Yohei
authors.initials: Y
authors.lastname: Oku
authors.forename: Hidetoshi
authors.initials: H
authors.lastname: Saitoh
authors.forename: Kimiaki
authors.initials: K
authors.lastname: Saito
authors.forename: Eileen N
authors.initials: EN
authors.lastname: Ogawa
authors.forename: Akitoshi
authors.initials: A
authors.lastname: Ishizaka
authors.forename: Kaori
authors.initials: K
authors.lastname: Kameyama
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kubo
mesh_terms: D000465:Algorithms; D000818:Animals; D005240:Feasibility Studies; D008168:Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000528:radiation effects*; D009010:Monte Carlo Method; D009068:Movement; D011656:Pulmonary Emphysema / Q000209:etiology / Q000473:pathology; D011817:Rabbits; D011833:Radiation Injuries, Experimental / Q000473:pathology*; D016634:Radiosurgery / Q000295:instrumentation* / Q000379:methods; D011879:Radiotherapy Dosage; D012119:Respiration; D036542:Tomography, Spiral Computed / Q000379:methods