Radiotherapy couches: is kevlar an obstacle? Attenuation study of three different tabletops. Issue 4 (25th July 2016)

• Record Type: Journal Article
• Authors: Silva, Célia; Mateus, Dalila; Vieira, Sandra; Rodrigues, Milton; Eiras, Margarida; Greco, Carlo
• Is Part Of: Journal of radiotherapy in practice. Volume 15:Issue 4(2015)
• Page Start: 346
• Page End: 353
• Publication Date: 2016-07-25
• Subjects: Calypso, -- tabletop, -- attenuation, -- carbon fiber, -- kevlar; Radiotherapy -- Periodicals; 615.842005
• DOI: 10.1017/S1460396916000297
• Languages: English
• ISSNs: 1460-3969

Abstract

Abstract: Introduction: Treatment tabletops are usually made of carbon fibre due to its high mechanical strength and rigidity, low specific density, extremely light and regularly considered radiotranslucent. Our clinic acquired a Calypso 4D Localization System where electromagnetic (EM) frequencies to detect implanted transponders in the patient are used. Carbon fibre is an electrical conductive material which interferes with EM frequencies. Therefore, in order to be able to use the Calypso System the carbon fibre tabletop in the treatment room must be replaced. It is our goal to determine the attenuation of the new, non-carbon fibre, tabletop in treatment delivery. Materials and Methods: Measurements were performed using an ionisation chamber inserted in a slab phantom positioned at the isocenter for 6, 10 MV, 6 and 10 flattening filter free (FFF) MV photon beams. These measurements were performed with and without tabletop for 0°, 30° and 60° beam angle for a True Beam STx linac, for 5×5 cm 2 and 10×10 cm 2 field size beams. The attenuation was calculated for each measurement for each tabletop. Results: At 0° incidence on the Exact IGRT Couch, the measured attenuation for 10×10 cm 2 was 2·8 and 2·1% for 6 and 10 MV beams, respectively. For the same field size was measured 3·3 and 2·6% attenuation for 6 and 10 FFF MV beams, respectively. At the same incidence and regarding the other tabletops, the calculated attenuation is lower. For 10×10 cm 2 field, there is 2·0, 1·4, 2·1 and 2·6% attenuation for 6, 10 MV, 6 and 10 FFF MV energy beams on the kVue TM Universal Couch. For the Kvue TM Calypso ® Couch 10×10 cm 2 irradiation field, the measurements were 1·6, 1·3, 1·9 and 1·5%, respectively. This tendency is observed for all gantry angles. Discussion: The attenuation outputs were definitely higher for the Varian Exact IGRT Couch when compared with the kVue tabletops. The attenuation measurements for the kVue tabletops were closer to each other. Nevertheless kVue TM Calypso ® Varian tabletop showed smaller mean attenuation of the beams than kVue TM Universal Tip Insert for all measurements. Conclusions: There was no loss in treatment quality administration due to beam attenuation in the tabletop when tabletops were exchanged because of Calypso system integration. There is no need to change between kVue tabletops whenever there is a regular treatment or a Calypso System guided treatment.