ESTRO 2023 - Abstract Book

S685

Monday 15 May 2023

ESTRO 2023

To identify dosimetric parameters associated with acute hematologic toxicity (HT) in endometrial cancer treated with volumetric modulated arc therapy (VMAT-RT). Materials and Methods Patients with uterine adenocarcinoma treated in our Institution from March 2019 to November 2021 were retrospectively enrolled in this study. All patients underwent adjuvant external beam radiotherapy with Volumetric modulated arc therapy (VAMT) strategy plus a brachytherapy boost on vaginal cuff. When indicated, adjuvant platin-based chemotherapy was administered after surgery in upfront or sandwich setting. Pelvic bone marrow was contoured for each patient and divided into three subsites: lumbosacral spine (LSBM), ilium (IBM) and lower pelvis (LPBM). The volume of each region receiving 10,20,30 and 40 Gy (V10, V20, V30, V40, respectively) and Dmean was collected. Hematological toxicity during radiotherapy treatment was graded according to the CTCAE V 5.0. Regression models were used to test associations between dosimetric parameters and HT. Results Data from 74 patients were retrospectively analyzed. Adjuvant external beam radiotherapy was delivered to the pelvis with Volumetric modulated arc therapy (VAMT) strategy for a total dose of 45 Gy, 1.8 Gy/fraction plus a brachytherapy boost on vaginal cuff for a total dose of 10Gy in 2 fractions weekly. Thirty-one patients developed during radiotherapy treatment an HT > grade 2. With a sensibility of 68.7% and specificity of 57.1%, V20 Gy of LSBM > 96% is associated with an increased Grade 2 or worse HT (95% Confidence Interval 0.50-0.74; p=0.049) No association between hematological toxicity and V10-20-30-40 or Dmean of IBM and LPBM were observed. Dosimetric parameters involving the lower pelvis had stronger association with hematological toxicity than those involving the ilium, even if not significant. Conclusion The volume of lombo-sacral pelvis receiving low-dose radiation (V20 LSBM >96%) seems to be associated with HT. Future investigations should seek to confirm these findings through the inclusion of these parameters in the planning process. PD-0813 Salvage stereotactic body radiotherapy in oligometastatic gynaecological cancer M. Midulla 1,2 , A. Fodor 1 , F. Zerbetto 1 , C.L. Deantoni 1 , R. Tummineri 1 , L. Giannini 1,2 , S. Broggi 3 , M. Torrisi 1,2 , F. Ferrario 1,2 , C. Chissotti 1,2 , S.L. Villa 1,2 , P. Mangili 3 , C. Fiorino 3 , S. Arcangeli 4,2 , N.G. Di Muzio 1,5 1 IRCCS San Raffaele Scientific Institute, Department of Radiation Oncology, Milano, Italy; 2 University of Milano-Bicocca, Department of Radiation Oncology, Milano, Italy; 3 IRCCS San Raffaele Scientific Institute, Medical Physics, Milano, Italy; 4 ASST- San Gerardo Hospital, Department of Radiation Oncology, Monza, Italy; 5 Vita-Salute San Raffaele University, Department of Radiation Oncology, Milano, Italy Purpose or Objective Patients (pts) with oligometastatic disease may benefit from treatment of all metastatic sites with stereotactic body radiation therapy (SBRT). In this retrospective study we analyzed the clinical outcomes of stereotactic treatment on different metastatic sites in pts with gynecological cancers. Materials and Methods From 4/09 to 10/22, 123 lesions in 68 pts were treated with SBRT. In 27 pts (39.7%) multiple SBRT were prescribed on synchronous and metachronous lesions. Eleven lesions were treated with Image Guided-helical Intensity Modulated Radiotherapy (IG-IMRT) to a median dose of 40(35-63) Gy in 5 (5-10) median fractions prescribed at 95% of the Planning Target Volume (PTV). One hundred twelve lesions were treated with robotic SBRT to a median dose of 40 (18-60) Gy in a median of 5 (1-8) fractions, prescribed at a median isodose of 80% (67-84%). Thirteen PTVs (10.5%) were in the same field of previous adjuvant or salvage radiotherapy performed with IG-IMRT with a median dose of 50.4Gy. Primary histology was: uterine in 41.5%, ovarian in 32.5%, cervical in 16.3%, vaginal in 5.7% and other (fallopian tubes and vulva) in 2.4% of lesions, respectively. Target locations were lymph nodes 50.4%, lung 32.5%, bone and soft tissue 4.9%, central nervous system 6.5%, and liver 5.7%. GTV was defined by the fusion of CT, PET/CT and/or MRI images. Toxicity was assessed using CTCAE version 4.03 criteria. Results Median age at the treatment was 62 years (3-88). Median follow-up was 18.2 months (0–75.4). Seventeen pts (13.8%) presented grade (G) 1-2 acute toxicity. No grade ≥ 3 acute toxicity was observed. Three pts presented late toxicity: one had G2 rib pain persistent up to 28 months after treatment, one had G1 hand paraesthesia, and the last one, irradiated on D12 (lytic lesion), a spine fracture 12 months later, with G3 bilateral leg pain and motor deficit. After treatment 56.9% of targets had a complete response, 25.2% a partial response, 6.5% a progressive disease, while 4.9 % of patients died and were lost to follow up. Local relapse free survival (LRFS) on a per lesion analysis, at 12 and 24 months, was 90.1 % and 86.2%, respectively, with a median LRFS not reached (See Fig.1). Distant metastasis free survival (DMFS), overall survival (OS) and cancer specific survival (CCS) were analysed on a per patient, and not per lesion basis. DMFS was 49% at 12 months, 26.9% at 24 months and 23.9% at 36 months, with a median of 10.5 months (See Fig2a). OS at 12, 24 and 36 months was 71%, 59.7% and 51.8%, respectively, with a median of 59.4 months (See Fig2b). Median CSS value at 12, 24 and 36 months was 74.3%, 62.8% and 57.1%, respectively (See Fig2c).