3D Matrix Phantom (Baltas Phantom)

A solid phantom of very high precision designed to be used to check the different reconstruction techniques incorporated in brachytherapy treatment planning systems and in radiotherapy departments. These may include orthogonal X-rays, semi-orthogonal X-rays, stereo-shift methods, isocentric techniques utilizing C-arm X-ray equipment or a radiotherapy simulator.

The Baltas Phantom can also be used for testing reconstruction algorithms and tools using CT based treatment planning procedures in modern brachytherapy. This can be realized within the framework of commissioning as well as constancy test procedures.

The phantom was designed by Dimos Baltas and is commercially produced by GfM Medizintechnik in Weiterstadt Germany.

The phantom is built from 6 slabs of 2 cm PMMA thickness. Each of the slabs has a squared shaped surface of 12 cm side length. At each of the five interfaces, 5 marker spheres made by radiopaque material are inserted, resulting thus in a total of 25 spherical markers building a matrix.

The phantom is thus cubic with 12 cm side length. In the central slab there is an additional marker embedded for easily identifying the horizontal axis of the phantom and of the marker matrix. The row number is engraved on the front side of the cube using radiopaque material. This simplifies the identification of the markers rows during the reconstruction process for the case of X-rays.

CT based reconstruction

Example of CT based reconstruction of the 3D-Matrix-Phantom using a 2.0 mm slice thickness and 2.0 mm slice spacing.


3D Matrix Phantom Flyer135.21 KB
3D Matrix Phantom User Instructions137.77 KB
ESTRO-EQUAL for Brachytherapy geometric check630.22 KB


  1. Baltas D., Quality assurance in Brachytherapy with special reference to the microSelectron-HDR, Activity International Selectron Brachytherapy Journal, Special report No. 2 (1993).
  2. European Guidelines for Quality Assurance in Radiotherapy, A Practical Guide to Quality Control of Brachytherapy Equipment, Booklet No 8, Venselaar J, Pérez-Calatayud J (Eds) (Belgium: ESTRO), 2004.
  3. Roue´A, Ferreira I, Van Dam J, Svensson H, Venselaar J., the EQUAL-ESTRO audit on geometric reconstruction techniques in Brachytherapy, Radiotherapy and Oncology 78: 78-83 (2006).