SU‐FF‐T‐140: Dosimetric IMRT Plan Verification and Daily Quality Assurance with a Two‐Dimensional Ionization Chamber Array

Abstract

Purpose: IMRT requires a more specified quality assurance program than the conventional techniques. In this work we present our solution for a full IMRT quality assurance program with two‐dimensional ionization chamber arrays (2D‐ARRAY, PTW‐Freiburg) containing daily checks and individual dosimetric plan verifications. Method and Materials: The used array (type 10024) has 27 × 27 ionization chambers arranged in a plane, with an entrance window of 5 mm × 5 mm each. The centers of the 729 single chambers are positioned at 10 mm distance from each other. Results: Our quality assurance program is divided into two parts: On a daily basis, as a morning check, the dose at the central axis, the flatness and symmetry as well as the MLC calibration and light/radiation field congruence are evaluated by a single measurement. For a patient specific IMRT plan verification, the calculated dose distribution of the patient is exported to a CT containing the phantom set‐up with the 2D‐ARRAY. The corresponding IMRT sequence is exported to the linear accelerator. The values calculated for the plane of the 2D‐ARRAY and the values measured with it are then compared. Conclusion: The daily QA program has been extensively tested. All important field parameters can be obtained in a single measurement per energy. Furthermore MLC misalignments can be detected with an accuracy of less then 1.0 mm, allowing an early warning for a necessary MLC recalibration. The described program for IMRT plan verification has been proved to be very useful for an easy and fast pre‐treatment quality assurance. The error detection capabilities will be discussed in detail and shown to be sufficient for standard IMRT plans. Conflict of Interest: This work was performed in collaboration with PTW‐Freiburg Dr. Pychlau GmbH, Freiburg, Germany.