A patient is being treated on the 6-MV beam to an opposed lateral whole brain (midline).The collimator setting is 14 × 18 with no blocks.The dose is 4000 cGy/20 fractions.The separation is 22 cm.What is the dose delivered to Dmax?

Question

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First the equivalent square must be determined.A 14 × 18 field equivalent square is 15.75.The entrance and exit dose must be calculated.The PDD must be determined at Dmax (entrance dose)and the exit dose.

A Patient Is Being Treated on the 6-MV Beam to an Opposed