title: Influence of backscatter radiation on cranial reconstruction implants.
abstract: OBJECTIVE
  We aimed to evaluate backscatter dose variations in different cranial bone implant materials in an experimental model designed to simulate post-operative radiotherapy.
  
  
  METHODS
  We assessed the radiation backscatter doses associated with sheet- and mesh-type titanium plates and hydroxyapatite (HAP) samples (porosity: 35%, 50% and 85%). The samples were irradiated with 6- and 10-MV photon beams from a linear accelerator. Measurements were obtained using an ionization chamber and radiochromic films cut from the same batch.
  
  
  RESULTS
  At 6 MV, the titanium sheet showed the highest peak for backscattered radiation, followed by (in decreasing order) HAP30%, HAP50%, titanium mesh and HAP85%. At 10 MV, HAP30% showed the highest peak, followed by HAP50%, titanium sheet, titanium mesh and HAP85%. The peaks were at different depths in the titanium and HAP samples. The thickness of the human scalp is approximately 7 mm; therefore, measurements were obtained 0-7 mm above the implants to assess the likely dose on the scalp. A comparison of the maximum dose on the scalp showed the titanium sheet had the highest dose at both 6 and 10 MV.
  
  
  CONCLUSIONS
  The backscatter dose differed with the density of the material and the backscatter depth was different for each material. Advances in knowledge: Ulcer formation due to radiotherapy after brain tumour depends on not only radiation but also the implant material. Therefore, the density and type of implant material should be considered when planning radiotherapy and selecting bone reconstruction materials.
authors.affiliation: 1 Department of Plastic and Reconstructive Surgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Sakamoto
authors.affiliation: 2 Department of Radiology, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Naoyoshi
authors.initials: N
authors.lastname: Koike
authors.affiliation: 2 Department of Radiology, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Takei
authors.affiliation: 2 Department of Radiology, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Mari
authors.initials: M
authors.lastname: Ohno
authors.affiliation: 3 Department of Neurosurgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Tomoru
authors.initials: T
authors.lastname: Miwa
authors.affiliation: 3 Department of Neurosurgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Kazunari
authors.initials: K
authors.lastname: Yoshida
authors.affiliation: 2 Department of Radiology, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Naoyuki
authors.initials: N
authors.lastname: Shigematsu
authors.affiliation: 1 Department of Plastic and Reconstructive Surgery, Keio University School of Medicine, Tokyo, Japan.
authors.forename: Kazuo
authors.initials: K
authors.lastname: Kishi
mesh_terms: D017886:Durapatite / Q000528:radiation effects*; D006801:Humans; D010315:Particle Accelerators; D019047:Phantoms, Imaging; D019736:Prostheses and Implants; D011879:Radiotherapy Dosage; D012542:Scattering, Radiation; D012886:Skull; D014025:Titanium / Q000528:radiation effects*
chemical_list: D017886:Durapatite; D014025:Titanium