Figure 1.

Images a‐c are used to illustrate the need for a dual CT/MR‐visible phantom for MRgRT modalities. This figure displays IROC‐Houston's Anthropomorphic Thorax phantom imaged in a GE Lightspeed CT simulator (a.) and Siemen's Magnetom Espree 1.5 T MR scanner (b–c). The phantom's tumor and lung were constructed out of polystyrene and compressed cork, respectively. The tumor is located in the phantom's left lung and is completely visible on a CT (a.) however, the tumor and surrounding lung tissue are not visually distinguishable in either a T1‐weighted (b.) or T2‐weighted (c.) MR image.