Dosimetric evaluation of intensity modulated radiation therapy for different duty cycles of the gated beam delivery

Aim of this study was to evaluate the extent of the error that the gating system incorporates into an intensity-modulated radiation therapy (IMRT) delivery for the different duty cycles of beam gated treatments (beam-interruption) by comparing the gamma between the dose planes.

Respiratory motion patterns was recorded in the real-time position management (RPM) software, which controls the triggering of the linear accelerator for the beam ON/OFF based on the predefined gating window. 10 IMRT plans consisting of 60 IMRT fields were delivered for three different duty cycles (20%DC, 30%DC and 40%DC) of gated and non-gated delivery. Planar dose measurements of IMRT delivery were performed with the commercially available two-dimensional ion chamber array and portal dosimetry. Gamma evaluation was carried out for the three different duty cycles of gated delivery with that of the reference of non-gated delivery, and the measured dose planes of gated and non-gated delivery were gamma analyzed with the treatment planning system (TPS) dose planes. Multileaf collimator (MLC) dynalog files were acquired and analyzed for the different duty cycles of gated and non-gated IMRT deliveries.

Gamma between the gated and non-gated dose planes were found within the 3% deviation.  Area gamma for the gated and non-gated delivery to the reference of TPS dose planes were found within the deviation of 6%.

Gamma comparison of the gated delivery with the reference of non-gated delivery results demonstrated that increasing the duty cycle reduced the deviation between the gated and non-gated delivery.