A comprehensive EPID-based 3D validation technique for TrueBeam-delivered VMAT plans

17th International Conference on the Use of Computers in Radiation Therapy

物理学;计算机科学

Ansbacher, W.^1,3 ; Gagne, I.M.^1,3 ; Swift, C.-L.^2

BC Cancer Agency, Vancouver Island Centre, Victoria BC, Canada^1

BC Cancer Agency, Vancouver Centre, Vancouver BC, Canada^2

Department of Physics and Astronomy, University of Victoria, Victoria, BC, Canada^3

关键词: 3D reconstruction;    Clinical use;    Cylindrical phantoms;    Dose reconstruction;    Portal images;    Pre-Treatment;    Technical improvement;    Treatment plans;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/489/1/012067/pdf
DOI  :  10.1088/1742-6596/489/1/012067

学科分类：计算机科学（综合）

来源: IOP

【 摘 要 】

Purpose: To develop and validate a pre-treatment EPI dosimetry method on Varian TrueBeam linacs using continuous imaging, with reconstruction in a 3D cylindrical phantom geometry. Methods: Delivery of VMAT plans with continuous imaging is currently possible only in Research Mode on TrueBeam linacs, with images acquired in a proprietary format. An earlier technique was adapted to take advantage of technical improvements in EPID delivery, and was tested under various acquisition conditions. The dosimetry of VMAT plans was evaluated at isocentre and within patient volumes that had been transferred to the virtual phantom. Results: Approximately 60 portal image projections per arc were found to be adequate for 3D reconstruction in phantom volumes of 28cm diameter. Twelve prostate, CNS and Head & Neck deliveries were evaluated in Research mode relative to the corresponding Eclipse (v.10) treatment plans, and to measurements on an ArcCheck device in Treatment mode. Mean dose differences at isocentre were within 2% for the three-way comparison, and in PTV volumes were within 1% (s.d. 1%). However, some discrepancies were observed in ArcCheck results that may be related to the small dimensions of certain VMAT apertures. Conclusions: EPI dosimetry with 3D dose reconstruction is an accurate, comprehensive and efficient pre-treatment validation technique for VMAT delivery. Although currently limited to a research mode on TrueBeam, it has the potential to be implemented for clinical use.