SU-E-T-760: Limited Data Set Commissioning for Photon Treatment Planning

Abstract

Purpose: Commissioning a linear accelerator is a large task, often requiring 6 weeks or more of intensive effort. We wished to establish whether it is possible to accurately commission a linac with a greatly reduced data set, supplemented by averaged beam data taken from similar machines. Methods: We collected 6MV photon data (beam profiles and output factors) from 40 Varian linacs, and looked at the amount of variation between machines in our measured data set, and between our data and vendor-supplied ‘gold’ data. From this, we determined a limited data set that would be sufficient to characterize the photon beam fully when supplemented with averaged data from other machines. We then tested the limited data set approach by comparing a photon model in the Eclipse planning system generated with either a fully measured data set, or the limited data set supplemented with averaged data. Results: The largest amount of variability in the photon output factor data came from the smallest and largest fields in the data set. The largest variability in beam profiles was in small fields, and in wedged field profiles. In our limited data set, we reduced the number of individual fields measured by 60%, and the number of measured output factors by 80%. We estimate that these reductions could reduce commissioning time by more than 40 hours. Point comparisons of planning system dose models created from full and limited data sets gave an average difference of 0.1 +− 0.17% for open fields, and 0.2 +− 0.44% for wedged fields, with the maximum difference seen for all fields of 1.5%. Conclusion: We have demonstrated that it is possible, using an averaged data set from many accelerators, to accurately commission an accelerator beam with a greatly reduced data set.