SU-F-T-546: A Radiobiological Comparative Study of Robotic and LINAC-Based Lung SBRT.

PURPOSE: To expand the dosimetric comparison of CyberKnife and Elekta Versa HD regarding their capability to perform SBRT in lung cases by including radiobiological measures, which can estimate the clinical impact of the observed differences.

METHODS: This study analyzes treatment data of 10 patients, who were treated with SBRT on Elekta Versa HD and replanned using CyberKnife. The original structure sets from the RayStation treatment plans were transferred to MultiPlan and were used for planning, with the exception of the PTV. Special attention was given to the following structures during optimization in MultiPlan: PTV (expanded off GTV instead of ITV), ipsilateral and contralateral lungs, and chest wall. For each patient, the same dosimetric constraints were applied to both plans. The dose volume histograms (DVH) of the targets and organs at risk (OAR) were computed and used to compare the dosimetric differences between the two modalities. Additionally, the tumor control probability (TCP), normal tissue complication probability (NTCP) and complication-free tumor control probability (P+) radiobiological indices were calculated and compared.

RESULTS: The dosimetric indices show a negligible differences (Versa - CK) for the PTV (mean dose difference of 1.7 Gy and average minimum dose difference of -0.3 Gy). For the OARs, the average differences in mean and maximum doses, which varied between 0.4 to 1.7 Gy and 1.1 to 4.7Gy, respectively. The average differences in the radiobiological indices were also similar TCP = 0.3±0.6%, Composite NTCP = 2.4±2.9%, and P+ = -.1±3.3%, respectively.

CONCLUSION: Both modalities managed to meet the same dosimetric goals equally well. The similarities between the dosimetric and radiobiological indices indicate that the two treatment modalities are comparable. A larger patient cohort involving patients of different complexities would give a better insight for this comparison.