SU-E-T-150: End to End Tests On the First Clinical EDGETM

Authors


Abstract

Purpose:

To quantify the sub millimeter overall accuracy of EDGETM, the dedicated linac based SRS/SABR treatment platform from Varian, using a novel End-to-End (E2E) test phantom.

Methods:

The new E2E test phantom developed by Varian consists of a cube with an outer dimension of 15×15×15 cm3. The phantom is equipped with an exchangable inner cube (7×7×7 cm3) to hold radiochromic films or a tungsten ball (diameter = 5 mm) for Winston-Lutz tests. 16 ceramic balls (diameter = 5 mm) are embedded in the outer cube. Three embedded Calypso transponders allow for Calypso based monitoring. The outer surface of the phantom is tracked using the Optical Surface Monitoring System (OSMS). The phantom is positioned using kV, MV and CBCT images. A simCT of the phantom was acquired and SRS/SABR plans were treated using the new phantom on the first clinical installed EDGETM. As a first step a series of EPID based Winston-Lutz tests have been performed. As a second step the calculated dose distribution applied to the phantom was verified with radiochromic films in orthogonal planes. The measured dose distribution is compared with the calculated (Eclipse) one based on the known isocenter on both dose distributions. The geometrical shift needed to match both dose distributions is the overall accuracy and is determined using dose profiles, isodose lines or gamma pass rates (3%, 1 mm).

Results:

Winston-Lutz tests using the central tungsten BB demonstrated a targeting accuracy of 0.44±0.18mm for jaw (2cm × 2cm) defined 0.39±0.19mm for MLC (2cm × 2cm) defined and 0.37±0.15mm for cone (12.5 mm) defined fields. A treated patient plan (spinal metastases lesion with integrated boost) showed a dosimetric dose localization accuracy of 0.6mm.

Conclusion:

Geometric and dosimetric E2E tests on EDGETM, show sub-millimeter E2E targeting and dose localisation accuracy.

Ancillary