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New BIPM facility for brachytherapy and x-ray imaging

The BIPM is running a series of international comparisons to meet the needs of the NMIs in the field of brachytherapy, a radiotherapy treatment in which calibrated radioactive sources are positioned inside the patient. The comparison concerns primary determinations of reference air-kerma rate using Ir-192 brachytherapy sources. The comparison measurements take place on-site at the NMIs, using two ionization chambers similar to those used at in hospitals for the calibration of therapeutic radiation beams: a thimble-type and a well-type chamber.

The stability and characterization of the thimble chamber is determined at the BIPM using the existing Co-60 facility for dosimetry of external radiotherapy beams whereas the stability of the well chamber needs to be determined by using the same kind of radioactive source designed for brachytherapy, which is manipulated by remote 'afterloading' machines. For this reason, the stability of the well chamber is determined using a Cs-137 check source at the BIPM, mounted on a rigid stem and placed inside the chamber.

Recently at the BIPM, a new facility has been designed and built to locate the Cs-137 check source and the well chamber. It has been equipped with a robotic arm to allow the remote manipulation of the source. The software to interact with the robot has been developed and enables the robot to remove the source from its shielding container, place it inside the well chamber and put it back inside its container once the measurements are finished. The following video shows the robot in action.

In addition, the facility was also designed to house a digital imaging system that comprises a portable x-ray tube and a flat panel detector. The robot, located in the middle of the measurement table, can rotate towards the imaging system and manipulate the instrument to be radiographed in the x-ray beam.

To install the new facility, an existing laboratory was refurbished to comply with current norms for radiation protection and security: the x-ray tube and robot are interlocked with the laboratory door, lead screens line the walls, additional lead is placed around the well chamber and an external lighting system warns when the robot is in use and when radiation is detected in the irradiation room.

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