Fifty-sixth annual meeting of the American association of physicists in medicine
SU-E-T-216: Intercomparison of CyberKnife and GammaKnife Stereotactic Radiosurgery Treatment Plans for Metastatic Brain Tumors
Over 40,000 patients are treated annually for metastatic brain tumors. A common method of treatment for these patients is stereotactic radiosurgery (SRS). Two commercially available options for treatment of SRS are the CyberKnife and GammaKnife. The purpose of this work was to perform a detailed comparison of the quality of the two techniques for the treatment of metastatic brain tumors using quantitative parameters.
Six patients with small metastatic brain tumors (Range: 2.2cc– 14.6cc) that had previously received SRS treatment via the GammaKnife system were planned for equivalent treatment using the CyberKnife treatment planning system. To quantify the quality of the individual plans, the conformity number (CN), homogeneity index (HI) and gradient score index (GSI) were measured and compared. Both plans were created to delivery equivalent tumor coverage (Range: 10–14Gy) to the equivalent prescription volume. This was typically 99% prescription dose coverage to the GTV for both plans.
The calculated average HI was 0.497±0.155 versus 0.600±0.049, CI was 0.596±0.159 versus 0.865±0.022, and GSI was 41.4±17.8 versus 65.1±20.09 for CyberKnife vs GammaKnife respectively. Lower HI values imply a higher uniformity of dose throughout the target. CI ideally would be 1.000, and the closest to this value is to one, the better is the conformality to the treated site. High values for GSI implies a steeper dose falloff from the tumor to normal tissue and therefore is preferable. For this study statistical significance was achieved for CI, however due to the small sample size differences in HI and GSI were not statistically significant.
This data suggests that SRS treatments on CyberKnife and GammaKnife are of similar quality, with Gamma Knife able to deliver a slightly more conformal plan for the treatment of brain metastases.