NBTXR3 Crystalline Nanoparticles and Radiation Therapy in Treating Patients With Soft Tissue Sarcoma of the Extremity

Inclusion Criteria: * Age: 18 years and older * Soft tissue sarcoma of the extremity or trunk wall, or localized in the posterior region of the neck (i.e., coronal section passing through the posterior limit of the ear) * Locally advanced soft tissue sarcoma,candidate to radiotherapy * Primary tumor or, * Relapsed tumor, localized out of already irradiated area or, * Sarcomas secondary to previous irradiation exposure due to other primary cancer * WHO performance score 0 to 2 * Adequate function of Bone marrow: * Adequate renal function * Adequate liver function * All female patients of childbearing potential must have a negative serum/urinary pregnancy test Exclusion Criteria: * Written Informed Consent not obtained, signed and dated * Patients with the following histological type: Gastrointestinal Stromal Tumors (GIST), embryonal or alveolar rhabdomyosarcoma, Ewing's sarcoma, osteosarcoma or chondrosarcoma, Kaposi's sarcoma, primitive neuroectodermal tumor or dermatofibrosarcoma protuberans * Soft tissue sarcoma of the trunk wall localized in the abdominal region, i.e. the region defined cranially by the xiphoid process of the sternum and the costal margins, and caudally by the line joining the anterior superior iliac spines, both limited by the perpendicular lines crossing both nipples * Angiosarcoma of the trunk wall because of its diffuse frontier * Metastatic disease (CT-scan verification) with survival expectation \< 6 months * Concurrent treatment with any other anticancer therapy * Absence of histologically or cytologically proven cancer at the first diagnosis * Previous neoadjuvant chemotherapy treatment given as an upfront of the current treatment line * Previous radiation therapy in relapse site of the soft tissue sarcoma (no radiation re-challenge is permitted) * Moderate and severe liver dysfunction * Hemolytic anemia * Autoimmune disease * Complete initial work up earlier than 4 weeks prior to patient registration * Patients unable to comply with scheduled visits, treatment plans, laboratory tests, and other study procedures. * Patients participating in another clinical investigation at the time of signature of the informed consent.