A patient is being treated on the 18-MV beam to a PA spine at a depth of 10 cm.The collimator setting is 10 × 13 with no blocks.The dose is 300 cGy per fraction.What is the dose delivered to Dmax?

Question

Quizplus · Accepted Answer

The dose delivered to Dmax is higher than the prescribed dose due to the buildup effect and the fact that the maximum dose (Dmax) occurs closer to the surface than at the prescribed depth (10 cm) for an 18-MV beam. The dose at Dmax is typically higher because the beam has not yet reached electronic equilibrium. Given the prescribed dose of 300 cGy at 10 cm depth, and knowing that the dose at Dmax is higher, 375 cGy is a reasonable estimate for the dose at Dmax, indicating an increased dose due to the buildup effect.

A Patient Is Being Treated on the 18-MV Beam to a PA