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Questions from Raphex 2005

  1. Sep 24, 2012 #1
    Dear members,
    I am frustrated by the Raphex exam questions. there are many I cannot solved. And the answer section is very brief for most questions.

    T 10. The total dose delivered at depth dmax, from a pair of parallel-opposed fields, expressed as a percentage of the total dose at mid-plane:
    A. Decreases as photon energy increases.
    B. Decreases as field size increases
    C. Increases as patient thickness increases.
    D. Is slightly less for an SSD setup than for an SAD setup.
    E. All of the above.

    T 11 . When treating a lung volume with off-cord parallel opposed-oblique fields, 10 MV photons
    would be preferable to 6 MV photons because:
    A. 6 MV would give inadequate dose in the build-up region.
    B. Lung corrections are more accurate with higher energy.
    C. The total dose at dmax is less with 10 MV
    D. The cord dose is less with 10 MV

    ANSWERS:
    T10. E Any factor that increases the PDD will decrease the total dose at dm,,x, compared with the total dose at midplane. Treating at SSD rather than SAD gives a slightly higher PDD.
    T 11 . C For parallel-opposed fields, the total dose at dm,,X, as a percentage of the dose at the isocenter, is lower for higher photon energy.


    Could anyone elaborate, please?
     
  2. jcsd
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