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Shielding Design

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  • 1. Rota%on  13:  Shielding  Design   (Mentors:  Edward  C  Pennington,   Sarah  McGuire)   By     Vibha  Chaswal,  Ph.D.  
  • 2. The  Problem        40I  x  125I  area  design  layout  and  shielding:   •   A  Dual  energy  Linear  Accelerator  room:  6  MV   low-­‐energy  and  18  MV  high-­‐energy  facility.          (IMRT  and  TBI  capable)   •   A  High  Dose  rate  Brachytherapy  Suite:  Ir-­‐192   •  A  PET/CT  Area  
  • 3. The  facility  designed  
  • 4. Assump%ons:  Linac  room   Overes%ma%ons  in  workload   8  h  day,  5  d  week–1,  50  pa%ents  per  week   Average  absorbed  dose  of  3  Gy  delivered  at  isocenter  per  pa%ent   40  %  pa%ents  18  MV  beam,  60  %  treated  using  6  MV  beam   Maximum  absorbed  dose  output  rate  at  1  m  of  15  Gy/min,  and  the  normal   rate  used  is  5  Gy/  min   •  The  isocenter  is  at  1  m  from  the  radia%on  source  for  this  facility.   •  IMRT  WorkLoad:       •  •  •  •  –  80  %  of  6MV  pa%ents  –  24  pa%ents  per  day  treated  as  IMRT   –  40  %  of  18  MV  pa%ents  –  8  pa%ents  per  day  treated  as  IMRT   •  6  MV  TBI  beam   •  Future  increase  of  18  MV  beam  to  60%  usage   Use  factor  of  walls:   •  Lateral  walls:  0.3  as  opposed  to  0.25  (IMRT  usage)   Sca`er  and  Leakage  angle  of  incidence:   All  sca`er  and  leakage  taken  at  the  minimum  angle  of  incidence  
  • 5. Linac  Room  
  • 6. Tedious  calcula%ons:  watch  out  for   errors!   •  The  wall  adjacent  to  the  HDR  vault  is  calculated  for  design   dose  of  0.02  mSv/week,  i.e.,  that  of  an  uncontrolled  area.     •  This  is  DEFINITELY  a  control  area  in  a  Radia%on  Oncology   department.  The  primary  wall  thickness  for  the  control  area   design  dose  is  173  cm  as  opposed  to  202  cm  calculated  in  the   report.   •  However,  this  error  lead  to  an  overes%ma%on.  An  error  of  the   opposite  kind  will  lead  to  an  underes%ma%on  of  shielding.   •  Since  this  wall  is  also  TBI  wall,  overes%ma%on  is  good.  
  • 7. Linac  room  roof  design   R   Q   6.44 m 2.22  m   2.12  m   1.83  m   2.1  m   4.8  m   2.7  m   3.3 m 0.72 m 1.3m
  • 8. Assump%ons:  HDR    and  PET/CT   HDR   •  HDR  Pa%ents  per  week  =  25   •  Dose  per  pa%ent  =  10  Gy  at  1  cm  from  the   source.   PET/CT   •  PET/CT  pa%ents:  15  pa%ents/week   •  F-­‐18  FDG  dose  is  555  MBq  (15  mCi)  with  an   uptake  %me  of  60  min    
  • 9. HDR-­‐room  
  • 10. PET  holding  area  and  PET-­‐CT  
  • 11. Thank  You!  

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