ESTRO 2024 - Abstract Book

S2093

Clinical - Sarcoma, skin cancer, melanoma

ESTRO 2024

Cataldo 1 , Viola Salvestrini 1 , Andrea Romei 1 , Chiara Mattioli 1 , Ilaria Morelli 1 , Ilaria Bonaparte 1 , Lucia Angelini 1 , Lorenzo Livi 1 1 Azienda Ospedaliero-Universitaria Careggi, Università di Firenze, Radiation Oncology, Florence, Italy. 2 Azienda Ospedaliero-Universitaria Careggi, Università di Firenze, Orthopedic Oncology and Reconstructive Surgery, Florence, Italy. 3 Azienda Ospedaliero-Universitaria Careggi, Università di Firenze, Radiology, Florence, Italy. 4 Azienda Ospedaliero-Universitaria Careggi, Università di Firenze, Histopathology and Molecular Diagnostic Unit, Florence, Italy. 5 Anna Meyer Children's University Hospital, Pathology Unit, Florence, Italy

Purpose/Objective:

Neoadjuvant radiotherapy to 50 Gy in 25 fractions is delivered in operable Soft Tissue Sarcoma (STS) patients to downstage the tumor and improve resectability, although at the expense of increased risk of wound dehiscence. Nonetheless, clear margin resection (R0) may not be achieved in tumors located in proximity of critical structures such as the neurovascular bundle (NVB), resulting in impaired local control. The aim of this study is to increase R0 rate through addition of an IMRT boost to the potential sites of suboptimal resection in STS patients receiving neoadjuvant RT. We report hereby the dosimetric, clinical and safety results from the first 10 patients enrolled in this trial.

Material/Methods:

We designed a prospective monocentric interventional single-arm Phase II study enrolling locally advanced STS eligible for surgery. RT is administered in 25 daily fractions to include the MRI-based Gross Tumor Volume (GTV) and peritumoral tissue at risk of microscopic spread (CTV1) to a dose of 50 Gy (2Gy/fraction), with SIB (Simultaneous Integrated Boost) intensification to the tumor/dissection plane interface (CTV2) to a dose of 60 Gy (2.4 Gy/fraction). CTV2 delineation is approved by both a Radiation Oncologist and Surgeon. A margin of 0.5 cm is applied to both CTV to obtain PTV1 and PTV2. Concurrent anthracyclines-based chemotherapy (ChT) is allowed up to 3 cycles. Primary endpoint is R0 resection rate. Secondary endpoints include pathologic complete response rate, objective response rate, overall survival, local and distant progression-free survival, acute and chronic toxicity rate. Pathologic complete (pCR) and near complete reponse (pNCR) were defined as 100% and 90-99% of necrosis rate, respectively. To assess an increase in R0 rate from 81% to 97% assuming β=80% e α=0.05, 33 patients will be included. Dose constraints are summarized in Table1. At least 95% of the PTV1 and PTV2 should be covered by 95% the prescription dose up to a maximum allowed dose of 107%.