Abstract Book

S877

ESTRO 37

surgery comparing to brachytherapy or three-dimensional conformal radiation therapy (3DCRT). The purpose of this study is to compare simultaneous-integrated boost (SIB) IMRT and SIB volumetric arc therapy (VMAT) in optimizing planning target volume (PTV) coverage and minimizing dose to organs-at-risk (OAR). Material and Methods Sixteen patients undergoing post-operative radiotherapy for lower extremity STS were assessed between 2013 and 2017. For each patient, two SIB treatment plans were proposed, one VMAT plan with 2 partial arcs, and one IMRT sliding-window plan with 6-8 tangential fields, in order to avoid the whole limb circumference. Both plans were optimized with a Photon Optimizer (PO) v13 algorithm, and calculated with Analytical Anisotropic Algorithm (AAA) v13. Treatments were evaluated using cumulative dose–volume histogram (DVH) data for OAR and PTVs. Prescribed dose was 66 Gy (2 Gy/fraction) for high-risk subclinical regions and 56 Gy (1.69 Gy/fraction) for lower-risk subclinical regions. PTV66 was defined adding 0.5-1 cm to CTV66 (tumor bed, surgical scar and margins: 1-2 cm longitudinal plane and 1.5 cm radially). PTV56 was defined adding 0.5-1 cm to CTV56 (tumor bed and margins: 4 cm longitudinal plane and 1.5 cm radially, including surgical tissues not covered in PTV66). OARs contoured were whole femur, neurovascular bundle, minimum skin corridor, normal tissue outside PTV56, joint and genitalia (testis in male and external genitalia in female). T-student test was performed for continuous related variables and SPSS 22.0 was used for statistical analyses. Results Eleven male (69%) and five female patients (31%) were included. The mean patient age was 60 years. The PTV of 7 patients (5 male, 2 female) extended into the pelvis. Both VMAT and IMRT showed very good target coverage, conformity (CI) and homogeneity index (HI). CI PTV66 was 0.98 (mean) ± 0.02 (standard deviation) (VMAT) vs 1.01 ± 0.04 (IMRT) (p<0.05). HI PTV66 was 0.09 ± 0.01 (VMAT) vs 0.08 ± 0.01 (IMRT) (p<0.05). IMRT delivered significantly lower skin corridor mean dose (10.4 Gy ± 6.8 Gy) compared to VMAT (14.7 ± 6.5 Gy) (p<0.05) (figure 1). There was a trend to a decrease in near-maximum absorbed dose (D2%) for all the OARs in VMAT plan, but both techniques showed comparable results (table 1).

Conclusion In patients with extremity STS, the use of more sophisticated techniques may reduce late sequelae and thus improve their quality of life. Both, IMRT sliding- window and VMAT, appear to be optimal techniques that achieve great conformality and homogeneity whilst reducing doses to normal tissues, in which VMAT is better. IMRT demonstrated significant technical superiority lowering dose to skin corridor, which can be decisive to reduce the risk of lymphedema and to preserve limb functionality. EP-1630 Single-institution experience with SBRT/SRS in the management of soft tissue and bone sarcomas M. Spalek 1 , A. Borkowska 1 , R. Madejek 2 , D. Kiprian 3 , P. Rutkowski 4 1 The Maria Sklodowska-Curie Memorial Cancer Center, Radiotherapy, Warsaw, Poland 2 Medical University of Warsaw, Students’ Scientific Society of Radiotherapy, Warsaw, Poland 3 The Maria Sklodowska-Curie Memorial Cancer Center, Department of Head and Neck Cancer, Warsaw, Poland 4 The Maria Sklodowska-Curie Memorial Cancer Center, Department of Soft Tissue/Bone Sarcoma and Melanoma, Warsaw, Poland Sarcomas are rare tumours that account for less than one percent of all adult solid malignant cancers. The standard treatment for all patients with localised sarcomas is surgery, usually combined with perioperative radiotherapy or chemotherapy. Management of metastatic sarcomas is based on systemic therapy, however the importance of local treatment is constantly increasing. Long-term disease control might be achieved after resection of limited or progressive metastases. Contemporary highly conformal radiotherapy techniques, such as stereotactic body radiotherapy (SBRT) or stereotactic radiosurgery (SRS) allow to obtain high local control rate (LC) in many primary and metastatic cancers, however their role in the management of sarcomas has not been yet established. Aim of the study The aim of the study was to determine the efficacy and toxicity of SBRT/SRS in the management of sarcomas. Material and Methods The study group was a cohort of patients with soft tissue and bone sarcomas treated in our cancer centre that received SBRT/SRS. The following parameters regarding Purpose or Objective Introduction