title: Verification of Dose Distribution in Carbon Ion Radiation Therapy for Stage I Lung Cancer.
abstract: To evaluate robustness of dose distribution of carbon-ion radiation therapy (C-ion RT) in non-small cell lung cancer (NSCLC) and to identify factors affecting the dose distribution by simulated dose distribution.
  
  
  
  Eighty irradiation fields for delivery of C-ion RT were analyzed in 20 patients with stage I NSCLC. Computed tomography images were obtained twice before treatment initiation. Simulated dose distribution was reconstructed on computed tomography for confirmation under the same settings as actual treatment with respiratory gating and bony structure matching. Dose-volume histogram parameters, such as %D95 (percentage of D95 relative to the prescribed dose), were calculated. Patients with any field for which the %D95 of gross tumor volume (GTV) was below 90% were classified as unacceptable for treatment, and the optimal target margin for such cases was examined.
  
  
  
  Five patients with a total of 8 fields (10% of total number of fields analyzed) were classified as unacceptable according to %D95 of GTV, although most patients showed no remarkable change in the dose-volume histogram parameters. Receiver operating characteristic curve analysis showed that tumor displacement and change in water-equivalent pathlength were significant predictive factors of unacceptable cases (P<.001 and P=.002, respectively). The main cause of degradation of the dose distribution was tumor displacement in 7 of the 8 unacceptable fields. A 6-mm planning target volume margin ensured a GTV %D95 of >90%, except in 1 extremely unacceptable field.
  
  
  
  According to this simulation analysis of C-ion RT for stage I NSCLC, a few fields were reported as unacceptable and required resetting of body position and reconfirmation. In addition, tumor displacement and change in water-equivalent pathlength (bone shift and/or chest wall thickness) were identified as factors influencing the robustness of dose distribution. Such uncertainties should be regarded in planning.
authors.affiliation: Gunma University Heavy Ion Medical Center, Gunma, Japan.
authors.forename: Daisuke
authors.initials: D
authors.lastname: Irie
authors.affiliation: Gunma University Heavy Ion Medical Center, Gunma, Japan. Electronic address: junsaito@gunma-u.ac.jp.
authors.forename: Jun-Ichi
authors.initials: JI
authors.lastname: Saitoh
authors.affiliation: Gunma University Heavy Ion Medical Center, Gunma, Japan.
authors.forename: Katsuyuki
authors.initials: K
authors.lastname: Shirai
authors.affiliation: Gunma University Heavy Ion Medical Center, Gunma, Japan.
authors.forename: Takanori
authors.initials: T
authors.lastname: Abe
authors.affiliation: Gunma University Heavy Ion Medical Center, Gunma, Japan.
authors.forename: Yoshiki
authors.initials: Y
authors.lastname: Kubota
authors.affiliation: Gunma University Heavy Ion Medical Center, Gunma, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Sakai
authors.affiliation: Gunma University Heavy Ion Medical Center, Gunma, Japan.
authors.forename: Shin-Ei
authors.initials: SE
authors.lastname: Noda
authors.affiliation: Gunma University Heavy Ion Medical Center, Gunma, Japan.
authors.forename: Tatsuya
authors.initials: T
authors.lastname: Ohno
authors.affiliation: Gunma University Heavy Ion Medical Center, Gunma, Japan.
authors.forename: Takashi
authors.initials: T
authors.lastname: Nakano
mesh_terms: D000368:Aged; D059925:Anatomic Landmarks / Q000000981:diagnostic imaging; D019540:Area Under Curve; D001842:Bone and Bones / Q000000981:diagnostic imaging; D002289:Carcinoma, Non-Small-Cell Lung / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D019583:Dose Fractionation, Radiation; D005260:Female; D063193:Heavy Ion Radiotherapy; D006801:Humans; D008175:Lung Neoplasms / Q000000981:diagnostic imaging / Q000473:pathology / Q000532:radiotherapy*; D008297:Male; D009068:Movement; D056888:Patient Positioning; D012372:ROC Curve; D011880:Radiotherapy Planning, Computer-Assisted; D020266:Radiotherapy, Conformal / Q000379:methods*; D012119:Respiration; D014057:Tomography, X-Ray Computed; D047368:Tumor Burden