Ni Qianxi, Department of Radiation Oncology ，Hunan Cancer Hospital/the Affiliated Cancer Hospital of Xiangya School of Medicine, Central South University，Changsha，China; Hunan Provincial Key Laboratory of Radiotherapy and Translational Medicine，Changsha ，China

Wong Peifong, Department of Radiation Physics，The University of Texas M.D.Anderson Cancer Center，Houston，USA

Zhang Jiutang, Department of Radiation Oncology ，Hunan Cancer Hospital/the Affiliated Cancer Hospital of Xiangya School of Medicine, Central South University，Changsha，China

Chen Ni, Department of Radiation Oncology ，Hunan Cancer Hospital/the Affiliated Cancer Hospital of Xiangya School of Medicine, Central South University，Changsha，China

Abstract
Purpose: This study aimed to analyze the dose attenuation caused by four kinds of commonly used commercial treatment couches (Elekta iBEAM evo Couch, Varian Exact Couch (Standard Couch), Varian Exact IGRT Couch, and BrainLAB imaging Couch) in IMRT and VMAT. Method: Six patients with prostate cancer were planned with both 6 MV 5-field , 7-field , 9-field IMRT plan and 2-arc (152º-212º and 210º-150º) VMAT plan in the treatment planning system (TPS). Compared the dose distribution difference with and without treatment couches in the TPS. The mean dose, dose covering 95% of the target volume, and the isocenter dose of the planning target volume were evaluated. Results: The dose attenuation was 1.46%-3.13% with Elekta iBEAM evo Couch, 0.72%-1.63% with Varian Exact Couch (Standard Couch), 0.86%-2.02% with Varian Exact IGRT Couch, and 1.51%-3.15% with BrainLAB imaging Couch. In the clinical evaluation, the dose attenuation was 1.24%- 3.15% in 5F- IMRT, 0.73%- 1.73% in 7F- IMRT, 1.39%-2.83% in 9F- IMRT, and 0.72%-1.78% in VMAT. Besides, the relative position between the patient and treatment couch was changed daily according to the record in the Elekta Mosaiq system. The shift of the treatment couches relative to the patient's position ranged from -2.00 cm to +2.00 cm. Simulation of treatment couch shift in the TPS showed that a treatment couch shift by 2 cm to the right or the left caused a maximum dose change of 0.65% and an average dose change of less than 0.30%. Conclusion: The dose attenuation caused by the treatment couch is obvious in IMRT and VMAT, suggesting the necessity of incorporating the accurate couch model in the TPS to minimize dose difference between the computed dose in TPS and the delivered dose to patient in actual treatment. The average dose attenuation is less in 7F-IMRT and VMAT than in 5F-IMRT and 9F-IMRT among four treatment couches. Varian Exact Couch (Standard Couch) and Varian Exact IGRT Couch cause less average dose attenuation than Elekta iBEAM evo Couch and BrainLAB imaging Couch. The position of patients relative to the treatment couch, which may vary in daily set-up, does not cause significant impact on the target dose in the treatment.

Keywords
Prostatic Cancer, Treatment Couch, Dosimetry, Intensity-modulated Radiotherapy(IMRT), Volumetric Modulated Arc Therapy(VMAT)

Cite this paper
Ni Qianxi, Wong Peifong, Zhang Jiutang, Chen Ni, Dose attenuation in intensity-modulated radiotherapy and volumetric modulated arc therapy caused by different treatment couches , SCIREA Journal of Clinical Medicine. Volume 4, Issue 4, August 2019 | PP. 109-119.

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