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

Abstract

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.

A validation of carbon fiber imaging couch top modeling in two radiation therapy treatment planning systems: Philips Pinnacle3 and BrainLAB iPlan RT Dose

“…Currently available couches include: Sinmed Mastercouch (Sinmed, Reeuwijk, The Netherlands) [11], Siemens IGRT carbon fiber tabletop [12], MED-TEC (USA) couch, BrainLAB imaging couch top [13], iBEAM Evo couch top EP (Medical Intelligence, Germany) [14], Contesse tabletop (Candor Aps, Denmark) [15] Kvue IGRT couch top (Qfix Avondale, PA, USA) and Dignity Airplate (Oncolog Medical AB, Uppsala, Sweden). These new imaging carbon fiber couch tops are thicker than the traditional tennis racquet and hence may have clinically significant photon attenuation.…”

Dosimetry comparison between volumetric modulated arc therapy with RapidArc and fixed field dynamic IMRT for local-regionally advanced nasopharyngeal carcinoma

“…Nowadays, RapidArc was developed mainly by the optimization of the multi-leaf collimators shape, the change of the dose rate delivery and the rotation of the gantry [5][6][7][8] . It was based on the volumetric modulated arc therapy technique and can obtain the similar distribution of the fixed IMRT.…”

Dosimetric effects caused by couch tops and immobilization devices: Report of AAPM Task Group 176

“…Numerous publications show a significant increase in surface dose when beams first transit carbon fiber couch tops at either normal or oblique incidence 6,[18][19][20][21][22][23][24] and show these to be larger than for the mylar-covered tennis racket couch top 25 (Table I). While there is some consistency in the methodology used for measuring and reporting the dose attenuation, there are large variations in the methodology used to determine and report the surface dose.…”

“…37 Several reports showed that couch attenuation can increase 4-fold as the beam angle ranges from 0 • to 70 • . 14,[21][22][23] As pointed out by McCormack et al, manually correcting the central axis dose for this attenuation may lead to an overdose or underdose to regions of the patient where the beam transited a different part of the couch top. 21 This is demonstrated in Fig.…”