Purpose: To determine the safety of delivering radiation with the CyberKnife system to a lung lesion using a 0-view plan where the tumor lies more than 5 cm from the spine tracking center.
Methods: The CIRS lung motion phantom has an anatomical spine built in for spine tracking on the CyberKnife system. The ball cube built into the CIRS phantom is within a 5cm radius of the spine. Therefore, an external ball cube was placed in a reproducible fashion outside of the phantom. This way the spine within the phantom was leveraged to deliver radiation to a ball cube that was 20cm away from the spine tracking align center. The Accuray Precision Planning System version 3.0.1 was used to generate a treatment plan to deliver dose to the ball cube while tracking on the spine (0-view lung tracking). The initial end-to-end delivery was done without any ball cube motion. A future delivery will incorporate motion. After the radiation was delivered the Accuray provided E2E film analysis software v4.0 was used to calculate a targeting error. TG-135 recommends a targeting error of less than 1.5mm for extreme end-to-end scenarios.
Results: The initial analysis within the E2E software yielded a targeting error of 1.77mm.
Conclusion: Though this is a bit higher than the recommendation given in TG-135, given the extreme nature of this delivery the result is quite impressive. Since the ball cube was at 20cm from the spine, the precision planning system was forced to eliminate many more beams than normal during the optimization (using VOLO). The reduction in beams caused the treatment plan used for the initial delivery to provide less dose coverage to the ball cube as normally would be by a plan which was allowed more beams.
Not Applicable / None Entered.