DOSIMETRIC VERIFICATION IN PHOTON BEAMS FOR ACUROS XB ALGORITHM

Abstract

The purpose of this study is to verify dosimetric accuracy of 6 MV X-ray beams for Acuros XB algorithm in Eclipse TPS by comparing measurements and calculations of beam characteristics and clinical applications. The beam characteristics were studied in various square and rectangular fields for PDDs, profiles and output factors by measurement in water phantom. The PDDs were measured by scanning with CC13 ion chamber, while in-plane and cross-plane profiles were acquired with PFD diode at 5, 10 and 20 cm depths. The output factors were measured at 10 cm depth using CC13 ion chamber. In clinical applications, the selected 15 cases in head, chest and pelvic regions of 3D-CRT, IMRT and VMAT techniques in homogeneous and heterogeneous medium were measured with CC13 ion chamber and compared with calculated dose in Eclipse TPS. The results of measured PDDs showed a good agreement to TPS with the average of δ1 (high dose, small dose gradient) at 0.16±0.64% and δ2 (high dose, large dose gradient) at 0.43±0.70 mm. Both measured in-plane and cross-plan profiles in all field sizes and all depths displayed the coincidence results with calculated profiles that showed δ2 less than 2 mm, δ3 (high dose, small dose gradient) within 3%, δ4 (low dose, small dose gradient) within 3%, and δ50-90 within 2 mm. The maximum output factors differences were -1.54%. For clinical application, the dose verification in homogeneous showed the maximum dose differences of 0.71% for 3D-CRT, -2.95% for IMRT and 2.70% for VMAT plans. While, inhomogeneous showed of the maximum dose error of 3D-CRT, IMRT, and VMAT plans at 0.61%, -2.27%, and -1.9% for 3D-CRT, IMRT, and VMAT plans, respectively. These dose differences were within the tolerance of ±3% for homogeneous and ±5% for heterogeneous medium as the recommendation from AAPM TG-53 and IAEA TRS 430. Therefore, the Acuros XB algorithm can be implemented in Eclipse TPS of clinical application radiotherapy.