Session Item

To present our clinical experience with a fully automated approach to SBRT treatment planning using Expedited Constrained Hierarchical Optimization (ECHO) to improve plan efficiency and quality.

From April 2017 to September 2019, 1492 patients underwent SBRT radiotherapy for paraspinal and other metastatic tumors with 1739 different ECHO produced plans. From October 2019, ECHO also produced plans for post-brachytherapy prostate patients receiving 25Gy in 5 fractions SBRT treatment. After contouring, a template plan using 9 IMRT fields was set up and sent to ECHO through an application program interface plug-in from the treatment planning system Eclipse®. The clinical criteria required by the institution to be always met were formulated as hard constraints (such as maximum dose, mean dose and dose-volume-histogram (DVH) constraints), were strictly enforced by the optimization. Other clinical criteria defined as “desired” (e.g., better PTV coverage, lower normal organs’ doses) were optimized as much as possible by solving sequential constrained optimization problems. A correction step incorporating leaf sequencing and scattering contributions into optimization, and smoothing fluence map of beams for delivery efficiency was in the final step of ECHO. Upon ECHO completion, the planner received an email indicating the plan was ready for review.

Among all the treated SBRT ECHO plans, 400 were for 24Gy in a single fraction, 1165 for 27Gy in three fractions, and the rest for various prescriptions doses with varied fractionations. Most plans were for paraspinal tumors with 174, 762 and 426 in cervical, thoracic and lumbosacral spine respectively. The median PTV size was 84 cc (range 7 - 633). The median time to produce one ECHO plan was 64 minutes (range 11-340), largely dependent on the field sizes. Over 90% of cases required just one run to produce a clinically accepted plan, the rest required additional run of ECHO with parameter tweak for physician special requests. All plans produced met or bettered the institutional clinical criteria. Excellent target coverage was achieved with PTV V100% averaged 93.0% ± 3.1% and PTV V95% averaged 98.2% ± 1.9%. ECHO plans were also highly conformal with Paddick Conformity Index averaged 0.86 ± 0.06. All ECHO plans were delivered after passing intuitional quality assurance process. We are currently using ECHO to generate over 80 SBRT plans a week in our clinic.

We successfully implemented a constrained hierarchial optimization method in our clinic for automated SBRT planning. ECHO has achieved the expected goals of producing consistently high quality clinical plans, in a reasonable time, that push normal tissue sparing as much as possible while respecting disease treatment goals. This has further resulted in an improved clinical workflow and shorter times between simulation and treatment in our clinic. We are working to expand use of the system to other disease sites.