TG-51 and Clinical Monitor Unit Calculations

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TG-51 and Clinical Monitor Unit Calculations

  1. 1. Treatment  Machine  Calibra0on   (TG51)   and  Monitor  Unit  Calcula0ons   By     Vibha  Chaswal,  PhD   Mentors:  Dr.  Alfredo  R  Siochi,  Edward  Pennington  
  2. 2. ObjecBves   •  Nuances  of  Clinical  MU  calculaBons     •  TG-­‐51  protocol:  clinical  reference  dosimetry   procedures  for  high  energy  photons  and   electron  beams  
  3. 3. Part  1:  MU  CalculaBons   •  Hand-­‐calculaBons  performed  over  number  of   cases   •  Performed  using  TPR  technique   •  MU  equaBons:   MUTPR = MU PDD = Dose / fx * beam weight K * TPR@ calc depth for fs@ calc * Sp fs@ calc * Sc coll fs * ISF * OAR@ calc depth for off -axis distance * TF *WF Dose / fx * beam weight K * PDD@ calc depth for fs @ surface, SSD * Sp fs@ surface * Sc coll fs * ISF * OAR@ calc depth for off -axis distance * TF *WF
  4. 4. Clinical  Reference  dosimetry  set-­‐up:  SAD  and  SSD   SSD   SAD   10x10 10 cm 10 cm 10x10
  5. 5. Hand  Calcula0ons  are  a  stepwise  transla0on   Dose  to  the  Water  Phantom  at  reference  condi0ons  =>  Dose  at  any  point  in  the  pa0ent     Source   Source   100  cm   Reference   calibraBon  point   Dose   CalculaBon   point  
  6. 6. Hand  MU  calculaBons   i.  Iso-­‐centric  calculaBons   ii.  Point  off  Isocenter  in  the  iso-­‐centric  plane  (AP/ PA)   iii.  Point  off  isocenter  off  the  iso-­‐centric  plane  (AP/ PA)   iv.  Whole  brain   v.  TangenBal  asymmetric  fields  –  Breast  plan   vi.  4  field  breast  –  PAB  /super-­‐calv  and  tangenBal   fields  
  7. 7. Error  eliminaBon  in  hand  calcs:  correct  field  size  esBmaBon  
  8. 8. Rearrange  MLCs  to  get  simpler  shapes….   ….Or  use  %  esBmaBon  for  blocked  area  
  9. 9. Error  elimina0on:  calc  point  depth   Either  measure  physical  depth  from  pinnacle,  or   use  effec0ve  depth  reported  by  Pinnacle  TPS  
  10. 10. Other  lessons   Account  for  missing  Bssue   Use  correct  ISF,  big  difference     MU  calculaBons  in  dmax  region  have   more  uncertainty  
  11. 11. TangenBal  breast/chest  wall  tx  and  4-­‐field  breast  tx   Involves:   -­‐  Constantly  changing  breast  contour  and   volume  in  the  field   -­‐  Oblique  surface  contour   -­‐  Asymmetric  Jaw   -­‐  Off-­‐axis  calculaBon  point  
  12. 12. TG-­‐51  CalibraBon   •  TG-­‐51  calibraBon  for  6X  photon  beam  –  Elekta   •  TG-­‐51  calibraBon  for  all  Photon  and  Electron   Energies  on  Oncor  A   Lessons:   -­‐  EffecBve  point  of  measurement  and  point  of   measurement  depths   -­‐  What  is  real  dmax  
  13. 13. Thank  you!!!  

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