Absorption measurements on a new cone beam CT and IMRT compatible tabletop for use in external radiotherapy.

With the development of intensity-modulated radiotherapy (IMRT), intensity-modulated arc therapy (IMAT), volumetric single arc therapy (RapidArc) and cone beam CT (CBCT) in 3D conformal radiotherapy, a need for new homogeneous treatment tabletops has evolved. Therefore, a new homogenous carbon fibre rotatable treatment tabletop Contesse has been developed. The intension was to create a CT compatible treatment tabletop accommodating all the standard treatment areas without add-on devises or the need to reconfigure the tabletop in everyday practice. At the same time, the absorption was sought to be minimized. Measurements of absorption with an ionization chamber have been performed for the main treatment geometries at normal and oblique angles together with build-up measurements at normal incidence. Absorption and build-up properties were shown to be comparable to those of other treatment tabletops with similar fixation devices. No artefacts from the tabletop are seen on CBCT scans. In order to reveal the absorption characteristics of tabletops, careful measurements at oblique angles including fixation devices on all clinically used tabletops must be performed. The Contesse tabletop is CBCT compatible, has acceptable absorption and is presently being used in the clinic for all patients, including IMRT and kilovoltage CBCT.