(Sunday, 7/29/2018) 3:00 PM - 6:00 PM
Room: Exhibit Hall
Purpose: Halcyon (Varian, Inc.) is a new treatment delivery system with 6-FFF-only energy and dual-layer MLC design. This study aims to establish a Knowledge-based Planning (KBP) model of oropharyngeal cancer based on Halcyon treatment plans, and to evaluate the difference between Truebeam plans and Halcyon plans using KBP model estimates.
Methods: Twenty oropharyngeal radiotherapy cases treated with Halcyon were included in this study. All the plans met constraints specified by HN002 protocol. A RapidPlan model was built in Varian Eclipse treatment planning system (Version 13.7) based on the twenty Halcyon IMRT plans. An additional five oropharyngeal radiotherapy cases planned and treated with 6X energy Truebeam plans were compared with the estimates from Halcyon KBP model dosimetrically. Dose-volume parameters compared between Halcyon KBP model predictions and Truebeam plans included: mean doses of left parotid, right parotid, esophagus, larynx, and oral cavity; and max doses of spinal cord, mandible, and brainstem.
Results: For the five test cases, the averages dosimetric parameters from Halcyon-Model KBP estimates vs. from Truebeam plans were (in Gy): 26.1±10.2 vs. 26.4±9.9 (left parotid), 27.7±16 vs. 31.7±15.5 (right parotid), 43.1±8.3 vs. 41.7±2.6 (spinal cord), 65.6±15.1 vs. 66.4±4.2 (mandible), 13.4±7.9 vs. 18.8±4.6 (esophagus), 29±9.8 vs. 32.8±6.9 (larynx), 36.2±19.3 vs. 44.9±9.1 (brainstem), and 26.6±10.2 vs. 31.1±9.9 (oral cavity). In general, most OAR doses of Halcyon plans are slightly lower comparing to Truebeam plans, but the difference is not statistically significant (p>0.05).
Conclusion: It is feasible to establish KBP model of oropharyngeal cancer based on Halcyon plans. Preliminary results indicate that plans from Halcyon system are of comparable quality for tumor coverage and critical structure sparing compared to Truebeam plans. More extensive comparison of more cases and additional disease sites is needed.
Funding Support, Disclosures, and Conflict of Interest: This project was supported by U24CA180803 (IROC) from the National Cancer Institute (NCI). The authors report no conflicts of interest with this study.
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