ESTRO 37 Abstract book

S105

ESTRO 37

PV-0197 Comparison of manual and two automated planning solutions for stereotactic brain radiosurgery M. Zamburlini 1 , J. Krayenbuehl 1 , A. Sonbadhar 1 , D. McDonnell 1 , M. Guckenberger 1 , N. Andratschke 1 1 University Hospital Zürich, Radiation Therapy, Zurich, Switzerland Purpose or Objective Stereotactic radiosurgery (SRS) is becoming increasingly more important in the management of brain metastases (BM). SRS treatment planning is challenging, because adequate beam geometry is patient dependent, which is particularly complex in the treatment of multiple BM (mBM) with a single isocenter. In this in-silico planning study, we compared two dedicated automatic treatment planning solutions (TPS) for BM with manual optimization. Material and Methods The planning study is based on 10 randomly selected patients treated with SRS at our hospital. For comparison purposes, the patients were classified in 3 groups: single BM (n=3); 3-5 BM (n=4) and >10 BM (n=3). This in-silico planning study compared manually generated treatment plans (Eclipse v13.6) with a fully automated planning solutions: Elements Multiple Brain Mets SRS (EL) (v1.5, Brainlab, Germany) and a semi-automated planning solution: Eclipse v15.5 with Hyperarc module (HA) (Varian Medical Systems, Palo Alto, USA). All plans were prepared for a TrueBeam linac with HD-MLC and a single isocenter. Plans were normalized to the PTV to have D100% > 99%. An inhomogeneous dose prescription was used with at least 113% of the prescribed dose (PD) covering 95% of each GTV and a Dmax of 123%-127% of the PD. Plans were compared based on target volume coverage, conformity index (CI) and dose to normal tissue. Results HA and CP achieved similar target coverage. However, EL was not able to achieve the requested dose inhomogeneity. EL plans were therefore re-normalized to achieve comparable GTV coverage. Table 1 and Figure 1 show the comparison in PTV and GTV coverage, as well as normal tissue sparing between the TPS. HA and CP show comparable PTV and GTV coverage. EL showed better PTV and GTV coverage, but less a favorable CI, due to the increased normalization to reach the necessary GTV mean dose. In the case of >10 BM, EL showed better brain sparing, probably due to the beam arrangement, which selected only a few targets to be treated for each given arc. Both EL and HA provided an advantage in terms of planning time with respect to CP. EL is fully automated and it required less than 5 minutes effective planning time. HA provides an automatic selection of the beam arrangement, which reduced planning time by 15 minutes or more for mBM depending on the number of lesions. Effective planning time remained at least 45 minutes for both HA and CP depending on the number of targets.

Conclusion EL and HA are able to provide clinically acceptable plans for SRS of single and mBM; however, the number of brain metastases treated with one single isocenter appears to influence the performance of the two automated planning solutions differently. Automation reduces planning time substantially compared to manual planning: effective planning time is less than 5 minutes for EL and HA provides a gain in effective planning time due to the automatic selection of beam geometry, but the optimization process still requires comparable planning time as CP. PV-0198 Clinical experience of automated SBRT paraspinal planning with constrained hierarchical optimization L. Hong 1 , M. Zarepisheh 1 , Y. Zhou 1 , Y. Yamada 2 , J. Mechalakos 1 , G. Mageras 1 , M. Hunt 1 , J. Deasy 1 1 Memorial Sloan-Kettering Cancer Center, Medical Physics, New York- NY, USA 2 Memorial Sloan-Kettering Cancer Center, Radiation Oncology, New York- NY, USA Purpose or Objective To present our initial clinical experience with automated treatment planning using expedited constrained hierarchical optimization (ECHO) to improve plan efficiency and quality for SBRT paraspinal plans. Material and Methods 124 patients underwent SBRT radiotherapy with 147 different paraspinal plans from April to Octob er, 2017. 52 patients (60 plans) received 24Gy in a single fraction, and 72 patients (87 plans) received 27Gy in three fractions. The tumor locations were in various parts of the spine with 25, 84, 33 and 5 in C, T, L and S spine respectively. After physician segmentation, a template plan using 9 IMRT fields was set up and sent to ECHO through an Eclipse API plug-in. ECHO would produce a Pareto optimal plan that satisfies hard constrains with best target volume coverage and lowest normal tissue doses. Upon ECHO completion, the planner received an email indicating the plan was ready for review and evaluation against the clinical planning criteria. The plan was accepted if all of the clinical criteria were met. If the plan did not meet all clinical criteria, the planner could adjust a limited number of parameters and initiate another round with ECHO. Results The PTV averaged 70 cc (range: 10-206) for single fraction cases and 122 cc (range: 18- 377) for three fractions cases. The total calculation time required to generate an ECHO plan was on average 147 minutes (range: 21-541), depending mainly on the size of the PTV. 105 plans (71%) were acceptable after a single ECHO run, 29 plans (20%) required 2 nd run (mainly to adjust one parameter that did not meet the clinical criteria) while 13 plans (9%) required 3 rd run (to accommodate specific dosimetric requests from the physician for those particular patients). All plans met or exceeded institutional clinical criteria (Table 1). For the 24Gy single fraction cases, PTV V100% was 93.3% ± 3.4%, PTV V95% was 97.6% ± 2.1%, minimum CTV dose was 17.4 ± 3.6 Gy, and minimum GTV dose was 22.1 ± 3.8 Gy. For the 27Gy three fractions cases, PTV V100% was 94.3% ± 2.5%, PTV V95% was 99.0% ± 1.1%, minimum CTV dose was 22.4 ± 2.5 Gy, and minimum GTV dose was 24.5 ± 3.6 Gy. Dose to spinal cord and other OARs is presented in the