69 Analysis and evaluation of a fixed vertical couch position technique in comparison with a placement based on tattoo and Couch Move Assistant on linacs Elekta Synergy S

Abstract

Introduction. In our department the daily patient setup is based on tattoos and the offsets, eventually registered in the Record and Verify software MOSAIQ (version 2.6), are then applied with the Couch Move Assistant (CMA). The procedure is: for the four first days of the treatment, a Cone Beam Computed Tomography (CBCT) is taken and the correction is applied even for a displacement of 1 mm. After the four fractions, the mean of a systematic error (SE), if detected, will be calculated and applied for the following fractions. For the prostate treatment if the means is greater than 4.5 mm, the mean of the offsets will be added automatically through MOSAIQ for the rest of the next fractions. When there is prostate marker (gold seeds), a CBCT is taken daily and no SE correction is applied. Based on the publication of Petillion [1] Petillion, S. et al. Efficacy and workload analysis of a fixed vertical couch position technique and a fixed-action–level protocol in whole-breast radiotherapy. J Appl Clin Med Phys 16, 279–290 (2015). Google Scholar et al. in 2015 for the whole breast radiotherapy, a fixed vertical couch position (FVCP) setup is expected to be more precise than a setup based on skin marks: because of skin mobility, imprecision of tattooing during simulation, precision of the CMA module. For a fixed couch vertical positioning, the setup would be as followed: patient setup in left-right (LR) and superior-inferior (SI) based on the skin marks. For the anterior-posterior (AP) setup, it would be based on table height measured in the Treatment Planning System (TPS). The aim of this study is to apply the same methodology for prostate treatment.