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Radiotherapy couches: is kevlar an obstacle? Attenuation study of three different tabletops

Published online by Cambridge University Press:  25 July 2016

Célia Silva ,
Dalila Mateus ,
Sandra Vieira ,
Milton Rodrigues ,
Margarida Eiras  and
Carlo Greco
Célia Silva*
Affiliation:
Centro Clínico Fundação Champalimaud, Lisbon, Portugal Escola Superior de Tecnologias da Saúde de Lisboa, Portugal
Dalila Mateus
Affiliation:
Centro Clínico Fundação Champalimaud, Lisbon, Portugal
Sandra Vieira
Affiliation:
Centro Clínico Fundação Champalimaud, Lisbon, Portugal
Milton Rodrigues
Affiliation:
Centro Clínico Fundação Champalimaud, Lisbon, Portugal
Margarida Eiras
Affiliation:
Escola Superior de Tecnologias da Saúde de Lisboa, Portugal
Carlo Greco
Affiliation:
Centro Clínico Fundação Champalimaud, Lisbon, Portugal
*
Correspondence to: Celia Silva, Outeiro Cacho, 8 Loureira, 2495-161 Santa Catarina da Serra, Portugal. E-mail: celia.psilva@gmail.com
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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 10flattening 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 cm2 and 10×10 cm2 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 cm2 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 cm2 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 kVueTM Universal Couch. For the KvueTM Calypso® Couch 10×10 cm2 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 kVueTM Calypso® Varian tabletop showed smaller mean attenuation of the beams than kVueTM 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.

Keywords

Calypsotabletopattenuationcarbon fiberkevlar
Type
Original Articles
Information
Journal of Radiotherapy in Practice , Volume 15 , Issue 4 , December 2016 , pp. 346 - 353
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Copyright
© Cambridge University Press 2016 

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