SU‐F‐T‐430: Validation of IBEAM Evo Couch Top for Different Relative Electron Density (RED) Combination During Photon Beam Dose Calculation in Monaco− Treatment Planning System

Abstract

Purpose:Validation of iBEAM™ evo couch‐top for different relative electron density (RED) combination during photon beam dose calculation in Monaco− TPS.Methods:The iBEAM™ evo couch‐top has two layers:outer carbon fiber (CF) and inner foam core (FC). To study the beam intensity attenuation of couch‐top, measured doses were compared with doses calculated for different REDs. Measurements were performed in solid water phantom with PTW‐0.125cc ion‐chamber positioned at center of the phantom with 5.3cm thickness slabs placed above and below the chamber. Similarly, in TPS, iBEAM™ evo couch‐top was simulated and doses were calculated for different RED combinations (0.2CF‐0.2FC, 0.4CF‐0.2FC, 0.6CF‐0.2FC, 0.8CF‐0.2FC, and 1.0CF‐0.2FC) by using Monte Carlo dose calculation algorithm in Monaco TPS (V5.1). Doses were measured for every 10 degree gantry angle separation, 10×10cm2 field size and 6MV photons. Then, attenuation is defined as the ratio of output at posterior gantry angle to output of its opposed anterior gantry angle (e.g.225°/45°). output fluctuation with different gantry angle was within ±0.21%. To confirm above results, dose‐planes were measured for five pelvic VMAT plans (360°arc) in PTW two‐dimensional array and compared with different calculated dose‐planes of above‐mentioned couch REDs. Gamma pass rates<1.00) were analyzed for 3%/2mm criteria.Results:Measured and calculated attenuation was in good agreement for the RED combination of 0.2CF‐0.2FC and difference was within ±0.515%. However, other density combination showed difference of ±0.9841%, ±1.667%, ±2.9241% and ±2.8832% for 0.4CF‐0.2FC, 0.6CF‐0.2FC, 0.8CF‐0.2FC, and 1.0CF‐0.2FC, respectively. Maximum couch‐top attenuation was observed at 110°–120° and 240°–250° and decreases linearly as the gantry angle approaches 180°. Moreover, gamma pass rate confirmed the above results and showed maximum pass rate of 96.23% for 0.2CF‐0.2FC, whereas others were 95.72%, 95.12%, 94.31% and 93.24%.Conclusion:RED value of 0.2CF‐0.2FC was found to be suitable for accurate couch‐top modeling for 6MV photon beam Monte Carlo calculations in Monaco TPS.