SU-E-T-705: Skin Dosimetry Comparisons of CyberKnife and Tomotherapy for Head-And-Neck Stereotatic Body Radiotherapy

Authors


Abstract

Purpose:

To perform a comparative evaluation of the skin dose in CyberKnife and Tomotherapy to predict an accurate dose in head-and-neck SBRT.

Methods:

Arbitrarily-defined planning target volume (PTV) near the skin was drawn on planning CT acquired from an anthropomorphic head-and-neck phantom that is used to perform the end-to-end test in CyberKnife. Calculation doses were obtained from Multiplan treatment planning system (TPS) using ray-tracing and monte-carlo (MC) algorithms for CyberKnife. For Tomotherapy, the skin dose was estimated with convolution superposition (CS) algorithm from Volo TPS. We selected 90% coverage of PTV in 3Gy prescription dose. We compared skin doses near target and at 5 cm far from the target. Optically-stimulated luminescent dosimeter (OSLD) measurements of radiation dose to the skin over the head-and-neck were made during PTV delivery in CyberKnife and Tomotherapy. Individually-calibrated OSLDs were placed on the surface of the phantom at a number of test positions. The measurement doses were compared with surface doses calculated from ray-tracing, MC and CS algorithms.

Results:

The calculated skin doses near target were estimated to be 78∼93% in ray-tracing, 50∼68% in MC and 78∼97% in CS. Skin doses near target were measured to be 54∼81% of the prescription dose in CyberKnife and to be 89∼104% of the target dose in Tomotherapy. The averaging differences between calculation and measurement values at the skin near target and at 5cm far from the target were 4.7%, 3.3%, and 4.8% in ray-tracing, MC, and CS, respectively.

Conclusion:

We verified the skin dose comparisons based on three algorithms used in Cyberknife and Tomotherapy. By the measurement values using OSLD, we found that skin dose could be minimized in CyberKnife compared to using Tomotherapy, which lead to a lower skin dose in head-and-neck SBRT. In the aspect of correlation between measured and calculated doses, MC was superior to ray-tracing and CS

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