title: Megavoltage cone beam CT near surface dose measurements: potential implications for breast radiotherapy.
abstract: OBJECTIVE
  Cone beam computed tomography (CBCT) is fast becoming standard on modern linear accelerators. CBCT increases the dose to regions within and outside the treatment field, potentially increasing secondary cancer induction and toxicity. This study quantified megavoltage (MV) CBCT skin dose and compared it to skin dose delivered during standard tangential breast radiotherapy.
  
  
  METHODS
  Dosimetry was performed both in- and out-of-field using thermoluminescent dosimeters (TLDs) and a metal-oxide-semiconductor-field-effect-transistor (MOSFET) detector specifically designed for skin dosimetry; these were placed superficially on a female anthropomorphic phantom.
  
  
  RESULTS
  The skin dose from a single treatment fraction ranged from 0.5 to 1.4 Gy on the ipsilateral breast, 0.031-0.18 Gy on the contralateral breast, and 0-0.02 Gy in the head and pelvic region. An 8 MU MV CBCT delivered a skin dose that ranged from 0.02 to 0.05 Gy in the chest region and was less than 0.01 Gy in the head and pelvis regions. One MV CBCT per fraction was found to increase the out-of-field skin dose from both the CBCT and the treatment fields by approximately 20%. The imaging dose as a percentage of treatment doses in the ipsilateral breast region was 3% for both dosimeters.
  
  
  CONCLUSIONS
  Imaging increases the skin dose to regions outside the treatment field particularly regions immediately adjacent the target volume. This small extra dose to the breasts should be considered when developing clinical protocols and assessing dose for clinical trials.
authors: Centre for Medical Radiation Physics, University of Wollongong, Wollongong, NSW 2522, Australia.
authors: Alexandra
authors: A
authors: Quinn
authors: Lois
authors: L
authors: Holloway
authors: Dean
authors: D
authors: Cutajar
authors: Nicholas
authors: N
authors: Hardcastle
authors: Anatoly
authors: A
authors: Rosenfeld
authors: Peter
authors: P
authors: Metcalfe
mesh_terms: D001943:Breast Neoplasms / Q000000981:diagnostic imaging* / Q000532:radiotherapy*; D054893:Cone-Beam Computed Tomography / Q000379:methods*; D005260:Female; D006801:Humans; D019047:Phantoms, Imaging; D011829:Radiation Dosage; D011874:Radiometry; D012867:Skin / Q000000981:diagnostic imaging / Q000528:radiation effects