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Development and Clinical Validation of a Robust Knowledge-Based Planning (KBP) Model for SBRT Treatment of Centrally Located Lung Tumors

J Visak*, R McGarry, M Randall, D Pokhrel, University of Kentucky, Lexington, KY

Presentations

(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: To develop a robust knowledge-based planning (KBP) model with commercially available Varian RapidPlan for early-stage, centrally-located non-small-cell lung tumors treated with stereotactic body radiation therapy (SBRT). The model was developed to be universally adaptable to clinics that adhere to Radiation Therapy Oncology Group (RTOG)-0813 protocol dose limiting criteria.

Methods: KBP model was trained using 86 high-quality clinically treated non-coplanar volumetric modulated arc therapy (n-VMAT) lung SBRT plans. Patients were treated using 6MV-flattening filter free beam and Acuros dose-calculation with 2.5mm calculation grid-size for heterogeneity corrections. Risk adopted prescriptions of 55 or 50Gy in 5 fractions were used to spare ribs and other organs at risk (OAR). Ten previously delivered SBRT plans (2 RLL, 2 RUL, 3 LLL and 3 LUL) were randomly selected and re-optimized with RapidPlan model. Planning Target Volume (PTV) was 29.5±20.3cc (range:7.5-75.6cc). KBPs were normalized for identical or better target coverage and compared to protocol OAR limitations without manual intervention.


Results: Conformity indices and maximal dose 2cm away from PTV showed no statistical difference between n-VMAT and KBP plans. The gradient distance (p<0.001) and gradient index (p=0.001) were lower for KBPs. KBPs presented on average 509 additional monitor-units (p=0.001). V20Gy was lower in KBPs (p=0.004). KBPs were compliant with RTOG-0813 with similar or better OAR sparing. Two KBPs with extremely difficult patient geometry showed higher doses to esophagus and bronchial-tree. With manual intervention doses could be reduced.


Conclusion: A robust universally-adaptable KBP RapidPlan model for early-stage, centrally-located lung tumors was developed. Plans met RTOG-0813 dosimetric goals in less than 15-min potentially offering shorter ‘simulation to treatment’ times (3-4 instead of 7 working days). Improved OAR sparing by KBPs may permit target dose escalation (50 to 55Gy). Implementing KBP modelling clinically for lung SBRT patients could provide more consistent and high-quality plans. Further clinical validation is underway.

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