title: Effects of shielding on pelvic and abdominal IORT dose distributions.
abstract: OBJECTIVE
  To study the impact of shielding elements in the proximity of Intra-Operative Radiation Therapy (IORT) irradiation fields, and to generate graphical and quantitative information to assist radiation oncologists in the design of optimal shielding during pelvic and abdominal IORT.
  
  
  METHODS
  An IORT system was modeled with BEAMnrc and EGS++ Monte Carlo codes. The model was validated in reference conditions by gamma index analysis against an experimental data set of different beam energies, applicator diameters, and bevel angles. The reliability of the IORT model was further tested considering shielding layers inserted in the radiation beam. Further simulations were performed introducing a bone-like layer embedded in the water phantom. The dose distributions were calculated as 3D dose maps.
  
  
  RESULTS
  The analysis of the resulting 2D dose maps parallel to the clinical axis shows that the bevel angle of the applicator and its position relative to the shielding have a major influence on the dose distribution. When insufficient shielding is used, a hotspot nearby the shield appears near the surface. At greater depths, lateral scatter limits the dose reduction attainable with shielding, although the presence of bone-like structures in the phantom reduces the impact of this effect.
  
  
  CONCLUSIONS
  Dose distributions in shielded IORT procedures are affected by distinct contributions when considering the regions near the shielding and deeper in tissue: insufficient shielding may lead to residual dose and hotspots, and the scattering effects may enlarge the beam in depth. These effects must be carefully considered when planning an IORT treatment with shielding.
authors: INESC TEC - INESC Technology and Science, Porto, Portugal.
authors: Alessandro
authors: A
authors: Esposito
authors: INESC TEC - INESC Technology and Science, Porto, Portugal.
authors: Taxiarchis
authors: T
authors: Sakellaris
authors: INESC TEC - INESC Technology and Science, Porto, Portugal.
authors: Patrícia
authors: P
authors: Limede
authors: Medical Physics, Radiobiology and Radiation Protection Group, IPO Porto Research Centre (CI-IPOP), Portuguese Oncology Institute of Porto (IPO Porto), Porto, Portugal.
authors: Filipa
authors: F
authors: Costa
authors: Medical Physics, Radiobiology and Radiation Protection Group, IPO Porto Research Centre (CI-IPOP), Portuguese Oncology Institute of Porto (IPO Porto), Porto, Portugal; Medical Physics Department, Portuguese Oncology Institute of Porto (IPO Porto), Porto, Portugal.
authors: Luis T
authors: LT
authors: Cunha
authors: Medical Physics, Radiobiology and Radiation Protection Group, IPO Porto Research Centre (CI-IPOP), Portuguese Oncology Institute of Porto (IPO Porto), Porto, Portugal; Medical Physics Department, Portuguese Oncology Institute of Porto (IPO Porto), Porto, Portugal.
authors: Anabela Gregório
authors: AG
authors: Dias
authors: Medical Physics, Radiobiology and Radiation Protection Group, IPO Porto Research Centre (CI-IPOP), Portuguese Oncology Institute of Porto (IPO Porto), Porto, Portugal; Medical Physics Department, Portuguese Oncology Institute of Porto (IPO Porto), Porto, Portugal.
authors: Joana
authors: J
authors: Lencart
authors: Medical Physics, Radiobiology and Radiation Protection Group, IPO Porto Research Centre (CI-IPOP), Portuguese Oncology Institute of Porto (IPO Porto), Porto, Portugal; Medical Physics Department, Portuguese Oncology Institute of Porto (IPO Porto), Porto, Portugal.
authors: Sandra
authors: S
authors: Sarmento
authors: INESC TEC - INESC Technology and Science, Porto, Portugal; Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Porto, Portugal. Electronic address: ccrosa@fc.up.pt.
authors: Carla Carmelo
authors: CC
authors: Rosa
mesh_terms: D000005:Abdomen / Q000528:radiation effects* / Q000601:surgery*; D004867:Equipment Design; D007432:Intraoperative Period; D008954:Models, Biological; D009010:Monte Carlo Method; D010384:Pelvic Bones / Q000528:radiation effects; D010388:Pelvis / Q000528:radiation effects* / Q000601:surgery*; D011829:Radiation Dosage; D011835:Radiation Protection / Q000295:instrumentation*; D011878:Radiotherapy / Q000295:instrumentation*; D011879:Radiotherapy Dosage
keywords: Dose distributions; Monte Carlo simulations; Pelvic IORT; Shielding