Evaluation and validation of tungsten fiducial marker-based image-guided radiotherapy

Abstract

In this research work, a simple homemade cubic phantom was designed to validate the Image-Guided Radiotherapy (IGRT) set up and verified with the help of tungsten fiducial markers (size 2–3 mm) inserted into the cubic phantom. Phantom made up of Styrofoam, was scanned with the help of 16 slice Toshiba CT scanner where each slice was of 1 mm thickness and HU level set to −1000. A radio-opaque contrast medium was rubbed on the phantom to visualize the scanner images. Once the iso-center had been marked on a phantom with the help of in-room positioning laser and the fields (RT-LAT and AP) were applied on the contoured body of the phantom in Varian’s ARIA-11 Eclipse dosimeter software, the same position of the phantom was reproduced on Varian’s Linear Accelerator DHX. Known shifts of 3.0 to 30.0 mm from the marked iso-center were applied on the phantom by moving the couch in all six directions one by one. On each applied couch shift, an x-ray image of the phantom was acquired with the help of an MV portal imager of Linac in AP and RT-LAT direction. This image was superimposed with a reference image of phantom and shift accuracy calculated by ARIA-11 software was noted down. It turned out that irrespective of the position of the phantom on the couch, the calculated corrected shift and deviation from reference position was always between ± 1–2 mm which is the required accuracy for IGRT according to International Atomic Energy Agency (IAEA). This process was repeated 40 times and each time, the corrected shift came out to be ± 1–2 mm. We can conclude that our system is safe and accurate enough to perfectly position the actual patient for IGRT.