QUESTION 1 Given a photon treatment, and assuming all else stays the same, how w

Question

QUESTION 1 Given a photon treatment, and assuming all else stays the same, how would the patient's skin dose change with each of the following (increase, decrease, or stay the same?) A. decrease B. increase C.stays the same Energy increases - Field size increases Lucite tray placed 10cm from the patient surface - 0.5cm thick bolus (tissue equivalent material) placed directly on the patient surface QUESTION 2 Suppose you have a medical condition that requires a 6MV AP image of your head. To minimize the dose to the lenses of your eyes, would you want to keep your eyes open or closed? open closed QUESTION 3 Why?

Explanation / Answer

a) Higher energy photon penetrate more deeply in to tissues and deliver a lower relative skin dose (decrease)
b) The field size is directly related to the amount of primary radiation entering the patient and the resulting dose distribution. A dose at any point results from both the primary and scattered radiation. Larger field sizes lead to increased generation of scattered radiation, which tends to increase skin dose (increase)
C) increase in dose due to the tray depends on the field size. (increase)
d) Bolus (build-up bolus) is material directly applied to the surface to increase the dose at the skin surface for megavoltage beams.(increase)

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