Dosimetric comparison of M6 CyberKnife plans optimized with Precision and RayStation 12A treatment planning systems.

Purpose: Treatment planning for CyberKnife (CK) (Accuray, USA) can be performed with Precision (Accuray, USA) or RayStation (RS) (RaySearch Laboratories, Sweden) treatment planning systems (TPS). RaySearch recently released a new version of the CK module in RS 12A. The objective of the study was to compare plan quality between RS 12A and Precision.

Methods: Fifty nine plans were optimized with both TPS and compared; 39 were for brain metastases and 20 were for vertebral metastases. To avoid bias in plan comparison, Precision plans were recomputed in RS with the dose algorithm and beam model of RS, and then compared to RS plans. The comparison was divided into 3 parts in order to reflect the potential of RS and the differences with Precision, in terms of technical aspects of delivery efficiency and dose distribution. We compared the dose to the target and to the organs at risk (OAR), the conformity index (CI), the gradient, as well as the number of monitor units (MU), and the number of beams and nodes. Finally, a global plan quality index (PQI) was calculated.

Results: RS plans showed an equivalent target coverage for brain metastases but worse for vertebrae. OAR sparing was improved in RS but with a lower CI compared to Precision. Using an appropriate planning methodology in RS, plans with comparable quality to Precision could be obtained, but at the cost of a longer optimization time. The PQI obtained with RS was better than Precision, except for some brain cases.

Conclusion: RS is an adequate alternative for CK planning as it is possible to obtain plan quality comparable to Precision. However, the optimization time is longer compared to Precision and more attention must be paid to the choice of the initial conditions in terms of the number of beams and nodes.