Effects of Siemens TT-D carbon fiber table top on beam attenuation, and build up region of 6MV photon beam

Abstract

Aim

This study deals with Monte Carlo simulations of the effects which the 550 TXT carbon fiber couch can have on the relevant parameters of a 6[[ce:hsp sp="0.25"/]]MV clinical photon beam in three field sizes.

Background

According to the reports issued by the International Commission on Radiation Units and Measurements (ICRU), the calculated dose across a high gradient distribution should be within 2% of the relative dose, or within 0.2[[ce:hsp sp="0.25"/]]cm of the isodose curve position in the target volume. Nowadays, the use of posterior oblique beam has become a common practice. It is clear that, in radiotherapy, the presence of the couch affects the beam intensity and, as a result, the skin dose.

Materials and methods

Firstly, Siemens linear accelerator validation for 6[[ce:hsp sp="0.25"/]]MV photon beam was performed, and satisfactory agreement between Monte Carlo and experimental data for various field sizes was observed. Secondly, the couch transmission factor for the reference field size and depth was computed, and the skin dose enhancement by the couch was assessed.

Results

The largest impact of the carbon fiber couch effect was observed for the 5[[ce:hsp sp="0.25"/]]×[[ce:hsp sp="0.25"/]]5[[ce:hsp sp="0.25"/]]cm² field size. Such evaluation has not been reported for this couch before.

Conclusion

Despite providing minimal attenuation for the primary radiation, the assumption that carbon fiber couches are radiotranslucent is not valid, and the effects of couches of this type on the transmission factor, and on the skin dose should be carefully investigated for each field size and depth.