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Since the ViewRay® system is a unique system integrated with MR system and Co-60 based radiation therapy system, not much experiences in the society were accumulated yet. Several studies already reported clinical feasibility of ViewRay® system with the results of patient treatment using ViewRay® system.
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The combined dose-rate of three Co-60 sources is 550 cGy/min which is comparable with that of commercial linac. 3) To compensate low dose-rate of Co-60, ViewRay® system uses a total of three Co-60 sources spaced 120° apart in a ring-type bore. Although penumbra of Co-60 is larger than that generated with a linac, ViewRay® system minimized the penumbra by adopting double-focused multi-leaf collimators (MLCs). 3) Since Co-60 is immune from the environments of MR system, differently from linear accelerator (linac), ViewRay® system adopted Co-60 radioisotope as a radiation source. 3) The ViewRay® system consists of on-board MR imaging system with 0.35 T static magnetic field and radiation therapy system with tri Co-60 sources. 1, 2) Recently, commercial MR-IGRT system (ViewRay®, ViewRay Inc., Cleveland, OH, USA) has been introduced to the radiotherapy field and implemented in the clinic. There has been a strong demand for magnetic resonance image guided radiation therapy (MR-IGRT) system in the field of radiotherapy due to MR image's superior power to distinguish soft tissues over computed tomography (CT) images. For E2E test, average gamma passing rate with 3%/3 mm criterion was 99.9%☐.1%. BJR supplement 25, PDDs between measured and calculated and output factors of each head were less than 0.5%, 1%, 1% and 2%, respectively. The deviations of output, PDDs between mesured vs. The average MLC positioning errors were less than 0.6 mm. Those between virtual isocenter and imaging isocenter were 0.6 mm, 0.5 mm and 0.2 mm, respectively. The deviations between radiation isocenter and virtual isocenter in x, y and z directions were 0 mm, 0 mm and 0.3 mm, respectively. The average couch movement errors in transverse (x), longitudinal (y) and vertical (z) directions were 0.2 mm, 0.1 mm and 0.2 mm, respectively. Every point within 10 cm and 17.5 cm radii about the isocenter showed deviations less than 1 mm and 2 mm, respectively. The values of SNR and Uniformity met the tolerance level. Every safety system of ViewRay operated properly. Finally, we performed gamma evaluations with a total of 8 IMRT plans as an end-to-end (E2E) test of the system. The deviations between measurements and calculation of percent depth dose (PDD) and output factor were evaluated. We performed reference dosimetry according to American Association of Physicists in Medicine (AAPM) Task Group 51 (TG-51) in water phantom for head 1 and 3. Couch movement accuracy and coincidence of isocenters (radiation therapy system, imaging system and virtual isocneter) was verified. In addition, we checked spatial integrity of the image. For imaging system, we acquired signal to noise ratio (SNR) and image uniformity. We verified safety functions of the ViewRay system.
![bjr supplement 25 aapm report bjr supplement 25 aapm report](https://cancerjournal.net/articles/2015/11/4/images/JCanResTher_2015_11_4_775_147727_f5.jpg)
The aim of this study is to present commissioning results of the ViewRay system.