Effect of the new carbon fiber bed board of Elekta Precise linear accelerator on the radiation dose

Abstract

Objective To investigate the dosimetric influence of pure carbon fiber treatment tabletop of Elekta Precise new linear accelerator in radiotherapy.Methods Surface-axis distance (SAD) technology was employed for the measurement.Two groups of fields were set and both of them were SAD opposed portals ( one of them went through the tabletop,while the other did not).A PTW electrometer and a 0.6 cm3 Farmer ionization chamber were utilized for comparison measurement.Then dose attenuation of the main table board,extended body board,the extended board for head,neck and shoulders,and the joints of these boards were calculated.Results Under the energy of 6 MV,the dose attenuations of the following locations were:1.4％ - 7.2％ at the main treatment table board; 2.8％ - 38.7％,1.4％ -30.1％,1.5％ -20.8％ and 1.4％ - 11.2％,respectively at distances of 1,4,7 and 8 cm from the joint of the main table board ;0.5％ - 5.0％ at the extended body board; 4.7％ - 15.4％ at distance of 1cm from the joint of the extended body board; 0.5％ -3.3％ at the neck position of the extended board for head,neck and shoulders; 5.3％ - 16.7％ at the shoulder positions; and 6.8％ -30.4％ at the joint between the extended boards and the main table board.Conclusions The dose attenuations of the new linear accelerator pure carbon fiber treatment tabletop vary at different locations. Considerable higher attenuations are observed at the table board joints than other locations. Key words: Treatment tabletop; Source-axis distance technology; Dose attenuation; Attenuation factor; Radiotherapy dose