Session Item

The purpose of the work is to present a method for optimizing beam quality control and correct operation of the Halcyon MLC collimator. The starting point for optimizing the control system was the MPC algorithm (Machine Performance Check). The development of independent methods for verifying the operation of the SX2 collimator and checking the beam stability of the Halcyon accelerator was based on algorithms independent of MPC. The developed quality control system was confronted with the MPC system in terms of quality and quantity.

Optimization of quality control of beam stability and correctness of SX2 collimator operation was based on MyQA application algorithms. Tests for the radiation beam included checking performance stability and energy constancy. The second group of beam-related tests are geometric tests involving the analysis of parameters such as symmetry, flatness, penumbra, size and center of the radiation beam. SX2 collimator tests are tests of stability, repeatability and accuracy of MLC leaf positioning, as well as correctness of MLC collimator operation for complex systems, for IMRT and VMAT techniques. MyQA software is based on predefined algorithms based on the guidelines of the AAPM 142 task group report. In order to adapt the guidelines of the AAPM-142 report to the needs of the Halcyon design solutions, a database of independent tests based on the myQA application algorithms was built and compared with the tests proposed by Varian in MPC software.

Analysis of the beam parameters for the built QA system turned out to be deeper than in the case of tests for the MPC algorithm. MPC tests regarding beam quality are consistency of performance and homogeneity. The results of both tests are presented in the form of a single value, with fixed tolerance levels of 4% and 2%. The proposed control system, in addition to the performance constancy test (image 1a) with two levels of tolerance (warning 1.0%, error 1.5%), extends the beam controls with energy constancy and symmetry, flatness, halftone, size and center position (image 1b). Tolerance levels for beam quality tests, unlike the MPC system, are a series of values ​​based on the guidelines of the IAEA TRS 389 report. Collimator SX2 control, in the MPC system is an analysis of the accuracy and reproducibility of settings for single leaves, for static systems. The proposed QA system allows testing the stability, repeatability and accuracy of MLC leaf positioning for dynamic systems.

The proposed, independent QA system, unlike the MPC system, allows a significant reduction in tolerance levels for performance stability and introduces their differentiation for individual beam geometric parameters. The presented QA system allows testing the accuracy of the MLC collimator for dynamic systems used in IMRT and VMAT techniques. Delivery time and time availability of results, as well as the ability to analyze time trends are the strengths of both systems.