Investigation of the reliability, accuracy, and efficiency of gated IMRT delivery with a commercial linear accelerator.

This work reports an investigation on the reliability, accuracy, and efficiency of gated intensity modulated radiation therapy (IMRT) delivery with a commercial linear accelerator. The dosimetry measurements of segmented multileaf collimated IMRT (SMLC-IMRT) were performed by using radiographic films and a two-dimensional diode array. Testing involved a series of IMRT fields from actual patients combined with some manually generated fields. To examine the delivery time, dosimetry plans of standard beamlet IMRT, direct-aperture-optimized (DAO) IMRT, compensator IMRT, and three-dimensional conformal radiotherapy with wedges were delivered with and without gating. The results demonstrated that the gated SMLC-IMRT can be reliably and accurately delivered on this type of accelerators, as long as extremely high interruption frequencies and very low number of monitor units per segment are avoided. Beam flatness exceeded 5% and monitor linearity deviated more than 3% for the gated operation with 2.5 s breathing cycle and 20% duty cycle with segment sizes less than 10 MU. Gating does not change multi leaf collimator (MLC) positioning accuracy. The DAO IMRT is preferred for gated delivery because of its short delivery time.