Medical Physics II Final

  1. light vs. radiation field
    QA tolerances
    Monthly check
    2 mm
  2. ODI
    QA tolerance
    • TG-40
    • Daily
    • 2 mm
  3. laser alignment
    QA tolerance
  4. TG-40
    • Daily:2 mm
    • TG-142(IMRT, SRS_SBRT)
    • IMRT-Daily:1.5 mm
    • SRS(SBRT)-Daily: 1 mm
    • Monthly IMRT +/- 1mm SRS(SBRT):<1mm
  5. QA
    MLC aggreement
    • Weekly-picket fence
    • Monthly-
    • Travel speed, loss of leaf speed 0.5cm/sec
    • Leaf position accuracy vs. gantry angle-1 mm
  6. gantry, collimator, couch isocenter
    QA
    2 mm or 1 degree
  7. monthly QA tests for the CT sim
    • Daily:
    • Alignment of lasers to midplane center
    • –CT number
    • –Image noise
    • –Spatial integrity (+ 1mm)
    • Monthly:
    • Laser positioning, spacing, etc.                     + 2 mmTable
    • motions, vert, long, lat,indexing  1mm
    • Spatial integrity + 1mm
    • Field uniformity + 5 HUCT
    • number accuracy (4-5 different materials)
  8. “rule of thumb” for electron energy loss in tissue
    2 MeV/cm
  9. electron range (Rp)
    The practical electron range. Seen on a depth-dose curve where the intersection of the depth dose slope and the bremsstrahlung tail.

    E/2

    ie-a  10 MeV beam has a range of 5 cm
  10. electron beam rule of thumb 80%
    E/3
  11. electron beam rule of thumb 90%
    E/4
  12. electron beam rule of thumb 50%
    E/2.8
  13. Describe the characteristics of electron isodose curves.
    The low -level isodose curves (<50%) bulge out beyond the field borders -The higher level isodose curves (>80%) tend to show lateral constriction, which becomes worse with increasing energy and depth
  14. Dd/Ddmax  x 100 = ?
    PDD
  15. PDD(increases/decreases) with E?
    increases
  16. PDD(increases/decreases) with fs?
    increases
  17. PDD(increases/decreases) with depth(beyond depth of max dose?
    decreases
  18. What are the parameters for calculating primary shielding?
    • 1)P is the permissible limit to an individual outside the barrier
    • 2)dpri is the distance from the target to the protected point
    • 3)W is workload or Gy / week produced by machine
    • 4)U is use factor or fraction of time the beam falls on the barrier
    • 5)T is the occupancy factor or fraction of time person will be in area adjacent to barrier
  19. ___ is the permissible limit to an individual outside the barrier
    P
  20. ___ is the distance from the target to the protected point
    dpri
  21. __ is Gy / week produced by machine
    W (workload)
  22. ____ is the fraction of time the beam falls on the barrier
    U (use factor)
  23. __ is the fraction of time person will be in area adjacent to barrier
    T is the occupancy factor
  24. What are the parameters for calculating secondary shielding?
    • PATIENT SCATTER
    • Bp = P / aWT * (dsec)2 * (dsca) 2 * 400/F
    • 1)a: the fraction of primary workload that will de scattered
    • 2)dsec: distance from patient to protected point
    • 3)dsca: distance from xray target to patient
    • 4)F: field size area
    • HEAD LEAKAGE
    • BL = 1000 P (dsec)2 / WT
  25. Secondary Shielding includes calculations for ____ and _____.
    • patient scatter
    • head leakage
  26. BL = ?
    head leakage(secondary shielding)
  27. a=?
    a: the fraction of primary workload that will de scattered
  28. dsec: ?
    distance from patient to protected point

    secondary shielding
  29. dsca=?
    distance from xray target to patient


    SECONDARY SHIELDING
  30. What is a maze & why is it used?
    A wall that is placed at the entrance of a vault & results in a 90 degree turn from the entrance into the vault to reveal the linacTypically used to reduce radiation levels at the room entrance so that a massive door is not neededMostly decreases head leakage that reaches the door so the door only shields for neutrons
  31. What type of shielding is used in the door?
    • First layer of lead (closer to source) reduces the energy of the incoming neutrons
    • Neutrons are absorbed in the second layer (BPE; borated polyethylene equivalent) Second layer of lead (away from source) attenuates captured gamma rays produced in the BPE (478keV)
Author
jaxkaty
ID
312785
Card Set
Medical Physics II Final
Description
Medical Physics II Final Last test(YAY!!)
Updated