title: Concomitant Imaging Dose and Cancer Risk in Image Guided Thoracic Radiation Therapy.
abstract: OBJECTIVE
  Kilovoltage cone beam computed tomography (CT) (kVCBCT) imaging guidance improves the accuracy of radiation therapy but imposes an extra radiation dose to cancer patients. This study aimed to investigate concomitant imaging dose and associated cancer risk in image guided thoracic radiation therapy.
  
  
  METHODS
  The planning CT images and structure sets of 72 patients were converted to CT phantoms whose chest circumferences (Cchest) were calculated retrospectively. A low-dose thorax protocol on a Varian kVCBCT scanner was simulated by a validated Monte Carlo code. Computed doses to organs and cardiac substructures (for 5 selected patients of various dimensions) were regressed as empirical functions of Cchest, and associated cancer risk was calculated using the published models. The exposures to nonthoracic organs in children were also investigated.
  
  
  RESULTS
  The structural mean doses decreased monotonically with increasing Cchest. For all 72 patients, the median doses to the heart, spinal cord, breasts, lungs, and involved chest were 1.68, 1.33, 1.64, 1.62, and 1.58 cGy/scan, respectively. Nonthoracic organs in children received 0.6 to 2.8 cGy/scan if they were directly irradiated. The mean doses to the descending aorta (1.43 ± 0.68 cGy), left atrium (1.55 ± 0.75 cGy), left ventricle (1.68 ± 0.81 cGy), and right ventricle (1.85 ± 0.84 cGy) were significantly different (P<.05) from the heart mean dose (1.73 ± 0.82 cGy). The blade shielding alleviated the exposure to nonthoracic organs in children by an order of magnitude.
  
  
  CONCLUSIONS
  As functions of patient size, a series of models for personalized estimation of kVCBCT doses to thoracic organs and cardiac substructures have been proposed. Pediatric patients received much higher doses than did the adults, and some nonthoracic organs could be irradiated unexpectedly by the default scanning protocol. Increased cancer risks and disease adverse events in the thorax were strongly related to higher imaging doses and smaller chest dimensions.
authors.affiliation: Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Department of Radiotherapy, Peking University Cancer Hospital & Institute, Beijing, China.
authors.forename: Yibao
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Department of Radiotherapy, Peking University Cancer Hospital & Institute, Beijing, China.
authors.forename: Hao
authors.initials: H
authors.lastname: Wu
authors.affiliation: Department of Therapeutic Radiology, Yale University, New Haven, Connecticut.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Chen
authors.affiliation: Department of Radiation Medicine, Hofstra North Shore-LIJ School of Medicine, Hempstead, New York.
authors.forename: Jonathan P S
authors.initials: JP
authors.lastname: Knisely
authors.affiliation: Department of Therapeutic Radiology, Yale University, New Haven, Connecticut.
authors.forename: Ravinder
authors.initials: R
authors.lastname: Nath
authors.affiliation: Key Laboratory of Carcinogenesis and Translational Research (Ministry of Education), Department of Radiotherapy, Peking University Cancer Hospital & Institute, Beijing, China.
authors.forename: Zhongsu
authors.initials: Z
authors.lastname: Feng
authors.affiliation: Beijing Key Laboratory of Medical Physics and Engineering, Peking University, Beijing, China.
authors.forename: Shanglian
authors.initials: S
authors.lastname: Bao
authors.affiliation: Department of Therapeutic Radiology, Yale University, New Haven, Connecticut. Electronic address: jun.deng@yale.edu.
authors.forename: Jun
authors.initials: J
authors.lastname: Deng
mesh_terms: D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001013:Aorta, Thoracic / Q000528:radiation effects; D049628:Body Size; D001940:Breast / Q000528:radiation effects; D002648:Child; D002675:Child, Preschool; D054893:Cone-Beam Computed Tomography / Q000009:adverse effects* / Q000379:methods; D005260:Female; D006321:Heart / Q000000981:diagnostic imaging / Q000528:radiation effects; D006801:Humans; D008168:Lung / Q000000981:diagnostic imaging / Q000528:radiation effects; D008297:Male; D008875:Middle Aged; D009010:Monte Carlo Method; D058958:Organs at Risk / Q000000981:diagnostic imaging / Q000528:radiation effects*; D019047:Phantoms, Imaging; D017785:Photons; D057285:Precision Medicine; D011522:Protons; D011829:Radiation Dosage; D013902:Radiography, Thoracic / Q000009:adverse effects / Q000379:methods; D061089:Radiotherapy, Image-Guided / Q000009:adverse effects* / Q000379:methods; D018570:Risk Assessment; D012737:Sex Factors; D013116:Spinal Cord / Q000000981:diagnostic imaging / Q000528:radiation effects; D035441:Thoracic Wall / Q000033:anatomy & histology / Q000528:radiation effects; D013909:Thorax / Q000033:anatomy & histology / Q000528:radiation effects*
chemical_list: D011522:Protons