Dosimetric verification of clinical radiotherapy treatment planning system

Abstract

Background/Aim. The aim of the study was investigating the significant difference in: a) the dosimetric calculation of the radiotherapy treatment planning system (TPS) in relation to the values obtained by measuring on the linear accelerator (Linac), b) the accuracy of the dosimetric calculation between the calculating algorithms Analytical Anisotropic Algorithm (AAA) and AcurosXB in various tissues and photon beam energies. Methods. For End-to-End test we used the heterogeneous phantom CIRS Thorax002LFC, which anatomically represents the human torso with set of inserts known relative electron density (RED) for obtaining a CT calibration curve, comparable to the "reference" CIRS 062M phantom. For the AAA and AcurosXB algorithms and for 6 MV and 16 MV photon beams in the TPS Varian Eclipse 13.6, four 3D conformal (3DCRT), and one intensity modulated (IMRT) and volumetric modulated arc (VMAT) radiotherapy plans were made. Measurements of the absolute dose in the Thorax phantom, by PTW-Semiflex ionization chamber, were carried out on three Varian-DHX Linacs. Results. The difference between "reference" and measured CT conversion curves in the bone area is 3 %. For 476 phantom measurements, the difference between measured and TPS calculated dose of (3-6) %, we had in 30 (6.3 %) cases. According to regression analysis, the standardized Beta coefficient for relative errors, 6 MV vs 16 MV, was 0.337 (33.7 %, p < 0.001). Mean relative errors for AAA vs AcurosXB, using Mann-Whitney test, for bones were 1.56 % and 2.64 % (p = 0.004). Conclusion. The End-to-End test on Thorax002LFC phantom proved the accuracy of TPS dose calculation in relation to the one delivered to the patient by Linac. There is a significant difference for photon energies relative errors (higher values are obtained for 16 MV vs 6 MV). A statistically significant minor relative error in AAA vs. AcurosXB was found for the bone.