Poster — Wed Eve—38: Comparison of IMRT Plan Quality from Two Different Linear Accelerator

Abstract

The purpose of this work was to determine whether two different types of linear accelerators manufacturers with similar MLC leaf widths deliver equivalent IMRT dose distributions for head and neck radiotherapy patients. In the first study, a retrospective analysis of 197 head and neck IMRT patients delivered on Siemens Primus and Elekta Synergy machines was undertaken to test statistical differences in machine type, monitor units, maximum target dose, and number of target doses. Both machines have 1 cm MLC leaves but have different linac head geometries. Plan were created using the direct machine parameter optimization (DMPO) routine on Philips' Pinnacle treatment planning system (TPS) system, in step and shoot mode. A multi‐variate analysis was used to test for significance, Pearson's correlations, and coefficients of determination. In the second study, a replanning exercise was conducted where deliverable plans from a Siemens machine was re‐optimized with an Elekta machine and vice‐versa. In the first study, there was no evidence of any significant difference in the IMRT plans. Elekta machines delivered more MUs than the Siemens units but the difference was not significant (). In the second study, the presentation of the dose distributions, DVHs, and mean dose to target and normal tissue structures were equivalent. However, approximately 15% more monitor units were delivered when plans were planned or re‐planned on the Elekta machine. This work suggests that for plans of comparable quality, Elekta machines deliver more monitor units than Siemens machines, likely due to differences in the geometric properties of the machines.