A patient is being treated on the 18-MV beam to an AP/PA stomach (midline).The collimator setting is 12 × 12 with no blocks.The dose is 4400 cGy/22 fractions.The separation is 24 cm.The cord is 4 cm from the PA.What dose is delivered to the spinal cord?

Question

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First the PDD for 12 cm, 4 cm, and 20 cm must be determined.The 12 cm represents the midline structure where the physician has prescribed 100 cGy per field.The 4 cm represents the spinal cord depth from the PA, and the 20 cm represents the cord depth from the AP.The dose to 4 cm and 20 cm must be determined and then added together.

A Patient Is Being Treated on the 18-MV Beam to an AP/PA