Abstract Book

S1014

ESTRO 37

on Eclipse Scripting Application Programming Interface (ESAPI) and RapidPlan knowledge-based planning. Material and Methods Using an in-house ESAPI script, the X jaws of a rectal VMAT plan were initially set to conform the planning- target-volume (PTV), and were gradually extended towards the isocenter (PTV center) with an incremental of 5 mm. Using these jaw pairs, 100 plans were automatically created and quantitatively evaluated using a comprehensive scoring function. A published RapidPlan model was evoked by RapidPlan to generate patient- specific optimization objectives without manual intervention. All candidate plans were first stored as text files to save storage space, and only the best, worst and conformal plans were consequently recreated for visual comparison. Results Although RapidPlan estimates dose-volume-histogram (DVH) based on individual anatomy and beam settings, it assumes conformal jaw opening to simplify the modeling, hence the predicted dose is independent from actual jaw settings. Therefore, ESAPI finalized all plans to dose- volume calculation and eliminated 26 plans before comparison due to unacceptable hot spots. The plan quality varied dramatically with different jaw settings. Table 1 and figure 1 displays organ scores and plan scores respectively. Trade-offs among different organs-at-risk (OARs) were collectively considered by the proposed scoring method, which identified the best and worst plans correctly (figure 2). The plan using conformal jaws was neither the best nor the worst of all candidates. Table1 Minimu m Maximu m Mean±S D Best * Wors t * Conform al Small bowel 0.85 1.59 1.000.1 4 0.9 1 0.99 0.98 Femor al head 0.82 1.08 1.000.0 6 0.9 5 1.04 1.06 Urinar y bladde r 0.85 2.04 1.000.2 5 0.8 6 0.99 0.91 * excluding 26 unacceptable plans. OAR Score=(MDVP+HDVP)/average(MDVP+HDVP). MDVP and HDVP indicate mean/high dose volume product per RTOG0822 protocol. Plan score=sum of OAR scores.

Conclusion A strategy has been developed to establish for each patient a fast robot travel path with minimal loss in plan quality relative to the original treatment plan. Overall, for prostate and lung cancer SBRT, the travel time reduced by more than 20%. EP-1875 Fully automated VMAT jaw optimization using Eclipse API Scripting and RapidPlan Y. Zhang 1 , Y. Huang 1 , H. Yue 1 , M. Wang 1 , S. Li 1 , J. Zhang 1 1 Key Laboratory of Carcinogenesis and Translational Research Ministry of Education/Beijing- Department of Radiation Oncology- Peking University Cancer Hospital & Institute, Department of Radiation Oncology, Beijing, China Purpose or Objective Eclipse treatment planning system has not yet been able to optimize the jaw positions for Volumetric Modulated Arc Therapy (VMAT). The arbitrary and planner- dependent jaw placements define the maximum field size within which multi-leaf-collimator (MLC) sequences can be optimized to modulate the beam. Considering the mechanical constraints of MLC transitional speed and range, suboptimal X jaw settings may impede the optimization or undermine the deliverability. This work searches optimal VMAT jaw settings automatically based