Question

The radiation oncologist has given a prescription to deliver 180 cGy to a midline depth in the pelvis using four equally weighted 18 MV x-ray beams at a 100 cm SAD (four field box) The AP/PA dimension is 22 cm and RL/LL dimension is 38 cm. The collimator size is 15 x 15-cm (AP/PA) and 15 x 12-cm (RL/LL) and MLCs are used making the treatment fields equivalent to a 12 x 12-cm field (AP/PA) and 12 x 10-cm field (RL/LL). If the calibrated output (10 x 10-cm) is 1.00 cGy/Monitor Units (MU) @ 103.0 cm (Dmx) with a 100 cm SSD, what is the dose rate at the Rx depth? How many MU are require for each field to fill the Rx?

Answer 1

SSD Di