ESTRO 2023 - Abstract Book

S765

Monday 15 May 2023

ESTRO 2023

D. Pezzulla 1 , G. Macchia 1 , S. Cilla 2 , M. Ferra 1 , M. Buwenge 3 , C. Romano 4 , S. Cammelli 3,5 , P. Bonome 1 , V. Picardi 1 , M. Boccardi 1 , M. Ferro 1 , M.A. Gambacorta 6,7 , A.G. Morganti 3,8 , F. Deodato 1,7 1 Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Radiation Oncology Unit, Campobasso, Italy; 2 Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Medical Physics Unit, Campobasso, Italy; 3 IRCCS Azienda Ospedaliero-Universitaria di Bologna, Radiation Oncology, Bologna, Italy; 4 Gemelli Molise Hospital – Università Cattolica del Sacro Cuore, Medical Physics Unit, Campobasso, Italy; 5 Alma Mater Studiorum Bologna University, Department of Experimental, Diagnostic, and Specialty Medicine - DIMES, Bologna, Italy; 6 Fondazione Policlinico Universitario A Gemelli IRCCS, UOC di Radioterapia Oncologica, Dipartimento di Diagnostica per Immagini, Radioterapia Oncologica ed Ematologia, Roma, Italy; 7 Università Cattolica del Sacro Cuore, Istituto di Radiologia, Roma, Italy; 8 Alma Mater Studiorum Bologna University,, Department of Experimental, Diagnostic, and Specialty Medicine - DIMES, Bologna, Italy Purpose or Objective To report the toxicity profile of a dose escalation study (Destroy-1) investigating the stereotactic radiotherapy (SBRT) retreatment of recurrences occurring later than 4 months after in-field radiation (RT). Materials and Methods In the frame of Destroy-1 trial, a phase I dose-escalation multiarm stereotactic radiotherapy (SBRT) clinical study, two arms (d) and (e) were conceived for retreatment of recurrence following prior in-field RT and were differentiated as follows: recurrences pre-irradiated with doses >60 Gy or recurrences in locations with previous small intestinal irradiation were recruited in arm (d), whereas recurrences in sites receiving a prior RT dose less than 60 Gy were recruited in arm (e). The total dose was escalated up to 45 Gy (arm d) or 50 Gy (arm e) through 6 levels, respectively (Table 1). Each cohort was evaluated for dose-limiting toxicity (DLT) and consisted of 6 patients; if one of the patients experienced a DLT, the cohort was expanded to 12 patients. DLT was defined as any radiation-related > Grade 3 toxicity (RTOG criteria) occurring within 6 months from SBRT. Adverse events occurring later than 6 months after SBRT were described as late toxicities, but were not considered in DLT evaluation. Results 117 lesions (41 lesions in the (d) arm and 76 in the (e) arm) accounting for 93 consecutive patients (M/F: 53/40; median age: 67 years; range 44-89) were treated from September 2004 to May 2022. About 92.5% of the patients had an ECOG performance status between 0 and 1, with coronary disease being the most frequent comorbidity (62.5%). Most patients had a primary lung (16.1%), pancreatic (12.9%) or prostate cancer (12.9%). The most common retreatment sites were pelvis (42.7%), thorax (28.2%) and abdomen (23.9%), with nodal recurrences accounting for the bulk of the lesions (59%). Median GTV was 8.9cc (0.35-146.9) and median PTV was 31.8cc (4.1-236.0). There was no acute toxicity above G2, and there was just one late toxicity >G2, consisting in a G4 soft tissue toxicity (abscess) in the pelvic area. More details on dose-level accrual and toxicity profile are shown in Table 1. Local control at 1-, 2- and 5-years was 93.0%, 76.0% and 67.1% respectively.

Conclusion Retreatment of recurrence with Stereotactic radiotherapy seems to be highly feasible in terms of toxicity profile. The end of the study is awaited in order to draw definite conclusions about the safety and efficacy of SBRT retreatment. OC-0920 Reirradiation for Diffuse Intrinsic Pontine Gliomas in Children: Clinical and Radiomic Analysis D. Wawrzuta 1 , M. Chojnacka 1 , K. P ę dziwiatr 1 1 Maria Sklodowska-Curie National Research Institute of Oncology, Department of Radiotherapy, Warsaw, Poland Purpose or Objective Diffuse intrinsic pontine glioma (DIPG) is a lethal pediatric brain tumor. Radiation therapy (RT) is the only effective treatment and standard of care. Reirradiation (rRT) remains an option at the time of progression. However, available data