ESTRO 2020 Abstract Book

S791 ESTRO 2020

distributions it was observed that plans with PCI ≥ 0.89 were 76% prior to the clinical implementation and 86% after the clinical implementation of the guiding value showing an increase of 10 percentage points (See Figure, red bars indicate PCI < 0.89 and green bars indicate PCI ≥ 0.89. Dashed line indicates mean PCI).

on MRI T1 sequence). A 2 mm isotropic margin was added to obtain the boost target volume (BTV). The PTV was defined as the entire vertebra containing the lesion, with an isotropic 2 mm margin. Doses of 30 Gy to BTV and 21 Gy to PTV were simultaneously prescribed in three fractions. All patients were planned with dual arc VMAT technique using 6 MV FFF beams. For AP plans, Autoplanning used a progressive optimization algorithm to continually adjust initial targets/OARs objectives. Tuning structures and objectives are automatically added during optimization to increase the dose fall-off outside targets and improve the dose conformity. Optimal coverage for BTV and PTV was considered D95% ˃ 95% of each prescription dose. Compliance of OARs constraints was considered a priority: spinal cord: Dmax<22 Gy and V18Gy<0.1 cc; spinal canal: V18Gy<0.1 cc. Dose statistics for target coverage, OARs sparing, conformity indexes (CI) and the R50% (ratio between volume receiving 50% of the prescribed dose and PTV volume) were compared. A Wilcoxon paired-test was performed for plan comparison (p < 0.05 as statistical significance). Results Both AP and MP plans were considered clinically acceptable. A summary of dosimetric results is reported in Table 1.

Conclusion A successful clinical implementation was performed and a decreased number of treatment plans with low PCI was observed, however, no statistically significant difference was found between the two distributions. The script is continued to be used in the clinic, also for other diagnoses, as guidance during the treatment planning process to achieve more conformal treatment plans. PO-1474 Automated VMAT-SBRT treatment planning for complex spinal metastases: a dosimetric analysis A. Ianiro 1 , F. Cellini 2 , C. Romano 1 , F. Deodato 3 , G. Macchia 3 , A. Zamagni 4 , M. Buwenge 4 , S. Cammelli 4 , L. Strigari 5 , L. Azario 6 , M. De Spirito 6 , V. Valentini 2 , A.G. Morganti 4 , S. Cilla 1 1 Fondazione di Ricerca e Cura Giovanni Paolo II, Medical Physics Unit, Campobasso, Italy ; 2 Fondazione Policlinico Universitario A. Gemelli, Radiation Oncology Department, Roma, Italy ; 3 Fondazione di Ricerca e Cura Giovanni Paolo II, Radiation Oncology Unit, Campobasso, Italy ; 4 University of Bologna- S.Orsola-Malpighi Hospital, Radiation Oncology Department, Bologna, Italy ; 5 S.Orsola-Malpighi Hospital, Medical Physics Unit, Bologna, Italy ; 6 Fondazione Policlinico Universitario A. Gemelli, Medical Physics Unit, Roma, Italy Purpose or Objective Stereotactic body radiation therapy (SBRT) has become a common option for the treatment of spinal malignancies. Dose escalation by simultaneous integrated boost (SIB) may improve local tumor control. This anatomical site presents a major challenge for planning optimization due to the complex relationship between targets and adjacent critical structures. We evaluated the feasibility of Pinnacle 3 Autoplanning engine for SBRT planning with VMAT technique and SIB strategy for spine treatments. Automatically generated plans (AP) were compared with manually-generated ones (MP) by expert medical physicists. Material and Methods Six patients with metastases to the body of lumbar and thoracic spine were included. GTV was defined as the macroscopic visible lesion at vertebral body level (based

Respecting all OARs constraints, AP and MP plans provided similar target coverage for PTV D95% (MP: 96.4 ± 2.2%, AP: 97.5 ± 4.8%, p = 0.173) but significant improvement for BTV (MP: 94.7 ± 7.2%, AP: 96.2 ± 8.8%, p = 0.046). AP plans exhibited higher conformity compared to MP plans for both BTV (MP: 2.4 ± 0.9%, AP: 2.3 ± 0.8%, p = 0.046) and PTV (MP: 2.5 ± 0.9%, AP: 2.3 ± 0.6%, p = 0.046), respectively. R50% was significantly better for AP plans (MP: 9.1 ± 2.0%, AP: 7.7 ± 1.3%, p = 0.028). Skin dose was significantly lower with AP plans. Last, planning time was reduced to about 1 hour for AP plans. Figure 1 shows the dose distributions for a representative patient.

Conclusion Automated SBRT-VMAT planning for complex spinal dose distributions is feasible. Pinnacle3 Autoplanning reported