An investigation of the couch coefficient accuracy of Exact IGRT Couch with Eclipse treatment planning system in Vital Beam Varian linear accelerator

Abstract

Purpose: The posterior oblique beams are increasingly common in radiotherapy techniques. The radiation beams traversing through the treatment couch would be attenuated and cause under-dosage in the tumor region. The attenuation of an IGRT carbon fiber Couch for different angles, energies, field sizes, measurement points, couch regions, and the ability of the Eclipse treatment planning system in dose prediction was investigated.

Materials and Methods: Vital Beam linear accelerator and Exact IGRT couch top from Varian were applied. At first, the couch coefficient was used to find the most attenuation angle. Then, at the most attenuation gantry angle, the attenuation measurements were performed in three measurement points of an inhomogeneous thoracic phantom using a farmer ionization chamber for three energies with six field sizes in three regions of an IGRT couch.

Results: In three regions of the IGRT couch and the angle of 130˚, the photon beam was most attenuated. The most significant difference between calculated and measured point doses was 1.855%.

Conclusion: The IGRT treatment couch in posterior oblique gantry angles decreased the dose in the measurement points due to gantry angle, field size, energy, and couch region. The Eclipse treatment planning system can sufficiently predict the tumor dose distribution.