Abstract
Purpose: Cobalt beams have exhibited superior dosimetric advantages for stereotactic radiosurgery/radiotherapy (SRS/SRT) of intra- and extracranial tumors compared to higher energy x-rays due to the sharper beam penumbra and the use of non-coplanar multiple source arrangement. This work investigates the potential clinical benefits of a novel rotating Gamma ray machine for SRS/SRT. Methods: The new SRS/SRT system (CybeRay, OUR United RT Group, Xian, China) consists of a ring gantry and a focusing treatment head with 16 Φ6.22 mm cobalt-60 sources. Each source has 7 collimators of 6, 9, 12, 16, 20, 25 and 35 mm diameter. The treatment head can swing 35° superiorly, allowing a total of 43° non-coplanar beam incident. The treatment couch provides 6-degrees-of-freedom motion compensation and the kV cone-beam CT system has a spatial resolution of 0.4 mm. Monte Carlo simulations were performed to compute plan dose distributions and to compare with 12 previously treated CyberKnife plans. Results: The CybeRay system had a 0.3 mm isocenter accuracy. The low-dose acquisition mode of the CBCT system provided fluoroscopy and 3D imaging at a dose level of <1 cGy. The maximum dose rate was >3 Gy/min at the center of a 16 cm diameter PMMA spherical phantom. The output factor varied from 1 to 0.739 for intracranial treatment using Φ20-Φ6 collimators, and from 1 to 0.698 for extracranial SRS/SRT using all 7 collimators. The beam penumbra (20%/80%) was 3.3 mm and 4.5 mm for the Φ6 and Φ35 collimators. Superior treatment plans were obtained with CybeRay for intracranial SRS/SRT with much reduced near target brain doses. CybeRay also produced favorable dose distributions for peripheral lung tumors using a partial-arc technique to spare the opposite lung and critical structures. Conclusion: The unique dosimetric properties of cobalt beams and the accurate stereotaxy/dose delivery make the new cobalt design an ideal system for advanced SRS/SRT of intra- and extracranial targets.
| Original language | English (US) |
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| Pages (from-to) | 2743 |
| Journal | Medical Physics |
| State | Published - Jun 2017 |
| Event | American Association of Physicists in Medicine: 2017 Annual Meeting - Duration: Jul 30 2017 → Aug 3 2017 |