On comparing the quality of head and neck IMRT plans delivered with two different linear accelerator manufacturers

The purpose of this work was to determine whether 2 different types of linear accelerators manufacturers with similar MLC leaf widths deliver equivalent IMRT distributions for head and neck radiotherapy patients. In this study, plans delivered with Siemens linacs were re-optimized with an Elekta linac and vice versa. To test for significance, paired t-tests were computed to examine differences in target and normal tissue doses and monitor units. Dose distributions, dose-volume histograms, and dose to targets and normal tissues were found to be equivalent irrespective of the linac type. However, approximately 15% more monitor units were delivered when planned on the Elekta machine (p < 0.002). Both linear accelerators provide plans of comparable dosimetric quality; however, Elekta machines deliver slightly more monitor units than Siemens machines. This increase is likely due differences in geometric properties of the machine head designs, as modeled in the treatment planning system.