ESTRO 2021 Abstract Book

S1230

ESTRO 2021

tumors)

S. Chilukuri 1 , S. Sundar 1 , A. Mathews 1 , K. Patro 2 , A. Reddy 3 , D. Sharma 1 , S. Nangia 1 , R. Jalali 1 1 Apollo Proton Cancer Centre, Radiation Oncology, Chennai, India; 2 Apollo Proton Cancer Centr, Medical Physics, Chennai, India; 3 Apollo Proton Cancer Centre, Radiation therapy, Chennai, India Purpose or Objective To analyze preliminary dosimetric and clinical outcomes of patients with moving tumors treated with pencil beam scanning proton therapy (PBS-PBT) as part of a prospective registry. Materials and Methods Twenty consecutive patients with thoracic and upper abdominal tumors underwent planning CT in free breathing (FB) or breath hold (BH) on the basis of tumor motion assessed on a 4DCT scan acquired using surface tracking. 4DCT scans were also acquired in BH to assess residual motion. All plans were generated using robust optimization to internal high-risk clinical target volume (iCTV-HR) and ensured that PTV coverage goals were also met. Volumetric re-scanning was used for patients treated with FB. Patients were treated using daily cone-beam CT (CBCT) and continuous surface tracking during treatment delivery. Weekly quality assurance (QA) imaging was performed to assess dose perturbations. Response evaluation and follow-up imaging was done as per standard institutional practice for each of the tumor sites. Results Eight patients of lung, 5 hepato-pancreatic (3-liver, 2-Pancreas) , 4 mediastinal (2-Thymoma, 1-Hodgkin’s Lymphoma, 1- Solitary fibrous tumor) and 3 upper gastro-intestinal tumors (2-esophagus, 1-gastro-intestinal junction) were treated to median dose and dose per fraction of 55.5CGE(30.6-60CGE) and 2.25CGE(1.8-7CGE) respectively. Median volume of iCTV-HR was 263.5cc(15-3600cc). Eleven patients were treated in FB and rest in BH. Median tumor motion in patients treated in BH and FB in x,y,z axis were 0.5,1.3,0.5cm and 0.2,0.4,0.3cm respectively; while maximum residual target motion in BH scans was 0.1,0.3 and 0.2cm. Median D98 of iCTV was 98.6% (93-100) and median PTV D95 was 98.5% (89-100%). All plans showed that iCTV-HR was robust for atleast 3mm setup error and 3.5% range uncertainty. Median in-room time per fraction was 38 minutes (22-47 minutes) and 24 minutes (18-39 minutes) for BH and FB respectively. Median breath holds per fraction for treatment and verification was 10 (8-17). Median number of QACT’s per patient was 4(2-5). Four patients required adaptive re-planning once while 3 patients required it twice. Five re-plans were attributed to tumor response, 2 patients to reproducibility concerns and 3 to dose perturbation to organs at risk. All patients completed their planned dose of treatment without any grade 3 toxicities. With a median follow up of 9 months, the local control in the treated lesions was 90%. Conclusion Image-guided PBS-PBT with surface guidance is safe and feasible for a variety of moving tumors. Preliminary clinical outcomes seem encouraging. PO-1502 Stereotactic body radiotherapy of lymph node metastases under MR-guidance C. Herder-Wagner 1 , F. Weykamp 2 , S. Regnery 2 , P. Hoegen 2 , C.K. Renkamp 2 , J. Liermann 2 , C. Rippke 2 , S.A. Koerber 1 , L. König 2 , C. Buchele 2 , S. Klüter 1 , J. Debus 2 , J. Hörner-Rieber 2 1 Heidelberg University Hospital, Department of Radiation Oncology, Heidelberg, Germany; 2 Heidelberg University Hospital, Department of Radiation Oncology, Heidelberg, Germany Purpose or Objective Stereotactic body radiotherapy (SBRT) is a non-invasive treatment alternative for lymph node metastases (LNM). Magnetic resonance (MR)-guidance offers superior tissue contrast and enables to treat targets in close vicinity to radiosensitive organs at risk (OAR). However, literature on MR-guided SBRT of LNM is scarce with no report on outcome parameters. Materials and Methods We report a subgroup analysis of a prospective observational study comprising patients with LNM. Patients received MR-guided SBRT at our MRIdian Linac between January 2019 and February 2020. Local control (LC), progression free survival (PFS) and overall survival (OS) analysis were performed using the Kaplan-Meier method with log rank test to test for significance (p<0.05). Our patient-reported outcome questionnaire was utilized to evaluate patients’ perspective. The CTCAE v. 5.0 was used to describe toxicity. Results Twenty-nine patients (72.4% with prostate cancer; 51.7% with no distant metastases) received MR-guided SBRT for in total 39 LNM. Median biologically effective dose (BED at α/β=10) was 51.3Gy (range: 43.2-100.0Gy). At 1-year, estimated LC, PFS and OS were 92.6%, 67.4% and 100.0%. Compared to baseline, six patients (20.7%) developed new grade I° toxicities (mainly fatigue). One grade II° toxicity occurred (fatigue), with no adverse event grade ≥III°. Overall treatment experience was rated particularly positive, whilst the technically required low room temperature still represents the greatest obstacle in the pursuit of the ideal patient acceptance. Conclusion MR-guided SBRT of LNM is a well-accepted treatment modality with excellent preliminary results. Long-term data is awaited to judge the true potential of MR-guided SBRT of LNM. PO-1503 A systematic review on ultra fractionated chemoradiation E. Scirocco 1,2,3 , F. Cellini 4,5 , A. Zamagni 2,3 , F. Medici 2,3 , C. Bellarosa 6,3 , G. Macchia 7 , F. Deodato 5,7 , S. Cilla 8 , V. Picardi 7 , L. Strigari 9 , M. Buwenge 2,3 , S. Rizzo 3,10 , S. Cammelli 2,3 , A.G. Morganti 2,3 1 Radiation Oncology, IRCCS - Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 2 Radiation Oncology, IRCCS Azienda Ospedaliero-Universitaria di Bologna, Bologna, Italy; 3 Department of Experimental, Diagnostic, and Specialty Medicine - DIMES, Alma Mater Studiorum Bologna University, Bologna, Italy;