WE‐E‐141‐02: An Improvement in IMRT QA Results and Beam Matching in LINACs Using Statistical Process Control

Abstract

Purpose: The purpose of this study is to apply the principles of Statistical Process Control (SPC) in the context of patient specific IMRT QA to set clinic specific action limits and evaluate the impact of changes to the MLC calibrations on IMRT QA results. Methods: Ten months of IMRT QA data with 247 unique QAs collected on three beam matched LINACS were retrospectively analyzed with a focus on the Gamma Pass Rate (GPR) and the average ratio between the measured and planned doses. Initial control charts and action limits were calculated. Based on this data, changes were made to the leaf gap parameter for the MLCs to improve the consistency between LINACS. This leaf gap parameter is tested monthly using a MLC sweep test. A follow up data set with 119 unique QAs was used to evaluate the impact of the leaf gap parameter change. Results: The initial data average GPR was 98.6 % with an SPC action limit of 93.7%. The average ratio of doses was 1.003 with an upper action limit of 1.017 and a lower action limit of .989. The sweep test results for the LINACS were −1.8%, 0%, and +1.2% from nominal. After the adjustment of the leaf gap parameter all sweep test results were within .4% of nominal. Subsequently, the average GPR was 99.4 % with an SPC action limit of 97.3%. The average ratio of doses was 1.003 with an upper action limit of 1.017 and a lower action limit of .989. Conclusion: Applying the principles of SPC to IMRT QA allowed small differences between closely matched LINACS to be identified and reduced. Ongoing analysis will monitor the process and be used to refine the clinical action limits for IMRT QA.

Implementation of Beam Matching Concept for the New Installed Elekta Precise Treatment System Medical LINACs in Indonesia

“…However, this output factor is not the main parameter for adjustment among the LINACs. The output factor data can be adjusted manually at the TPS, in accordance to the modeling that has been obtained [8].…”

“…The implementation of the beam matching concept to several LINACs should be accompanied by adequate maintenance and Quality Assurance (QA) processes, to ensure the suitability of dosimetry parameters among the LINACs. There is a published paper discussing QA in beam matched LINAC for several tumor case data [8,9].…”

“…One method to verify the measurement results uses the gamma index (γ-index), a parameter used to determine suitable dosimetry from two-dose distribution [6,8,9]. In this case, two-dose distribution has a definition that a pair of dose distribution obtained from dosimetry measurement among LINACs can be compared.…”

Verification of Surface Dose for Flattening Filter and Flattening Filter Free Beams in Beam-Matched Medical Linear Accelerators

“…Many researchers were reported about the performance of beam-matched linear accelerators (Kairn et al, 2015;Bhangle et al, 2011). Gagneur and Ezzell (2013) and Xu et al, (2019) reported the patient's specific quality assurance of VMAT, SBRT/SRT for beam-matched linear accelerators. To the best of our knowledge, we could not find any study-related to the surface dose measurement for beam-matched linear accelerators.…”