ESTRO 2023 - Abstract Book

S791

Monday 15 May 2023

ESTRO 2023

Conclusion In this cohort of patients treated with stereotactic arrhythmia radiotherapy, patient 1 had a large intra fraction motion exceeding the action level of 3 mm residual set up error vector length after single CBCT match evaluation. This prompted an online NAL imaging procedure for patient 2 to 7. To avoid problems with treatment delivery the online NAL imaging procedure will be continued for future patients in the STARNL-2 trial. OC-0943 Linac-based STereotactic Arrhythmia Radioablation for atrial fibrillation: dosimetric evaluation A. Fiorentino 1 , F. Gregucci 2 , A. Di Monaco 3 , A. Surgo 4 , R. Carbonara 5 , M.P. Ciliberti 6 , M. Caliandro 7 , M. Grimaldi 8 , F.C. Di Guglielmo 9 , E. Paulicelli 10 , I. Bonaparte 10 1 General Regional Hospital, Radiation Oncology, Acquaviva delle Fonti, Italy; 2 General Regional Hospital F Miulli, Radiation Oncology, Acuqviva delle Fonti, Italy; 3 General Regional Hospital F Miulli, Cardiology, Acuqviva delle Fonti, Italy; 4 General Regional Hospital F Miulli, Radiation Oncology, acquaviva delle Fonti, Italy; 5 General Regional Hospital F Miulli, Radiation Oncology , Acquaviva delle Fonti, Italy; 6 General Regional Hospital F Miulli, Radiation Oncology, Acuaviva delle Fomti, Italy; 7 General Regional Hospital F Miulli, Radiation Oncology, Acuaviva delle Fonti, Italy; 8 General Regional Hospital F Miulli, Cardiology, Acquaviva delle Fonti, Italy; 9 General Regional Hospital F Miulli, Radiation Oncology, Acquaviva delle Fonti, Italy; 10 General Regional Hospital F Miulli, Radiation oncology , Acquaviva delle Fonti, Italy Purpose or Objective Treatment approach for elderly patients with atrial fibrillation (AF) is difficult. A prospective phase II trial evaluating LINAC based stereotactic arrhythmia radioablation (STAR) safety in this population started in 2021. Here, dosimetric and planning data were reported. Materials and Methods A vac-lock bag was used for patients’ immobilization in the supine position and a Computed Tomography (CT, 1mm slice thickness) was performed. The clinical target volume (CTV) was identified by radiation oncologist and cardiologist and was defined as the area around pulmonary veins. An internal target volume (ITV) was added to CTV to compensate heart and respiratory movement. The planning target volume (PTV) was defined adding 0-3mm to the ITV. STAR was performed in free-breathing with a PTV prescription total dose (Dp) of 25Gy/1 fraction. A “simultaneous integrated protection” dose distribution was created at the interface between PTV and organs at risk in order to ensure the tolerability of critical structures. Flattening Filter Free Volumetric Modulated Arc Therapy (VMAT) plans were generated, optimized and delivered by TrueBeamTM (Varian Medical System). Image-guided radiotherapy with Cone Beam CT and Surface-Guided RadioTherapy with Align-RT (Vision RT) were employed. Results From May 2021 to March 2022, 10 elderly patients were treated: median age was 79.5 years old (range 72-90), 70% of patients were female. In terms of 4D-CT data, the average Cohort displacements of the CTV during the respiratory phases are as followed: the average displacements in Medio-lateral (M-L), Antero-posterior (A-P) and Superior-Inferior (S-I) directions for CTVright and CTVleft of -0.01; 0.01; 0.09; 0.01; -0.01; 0.09 cm, respectively. However, only S-I movements reported a motion amplitude of 0.6 cm, while for M-L and A-P an amplitude of 0.1 cm was documented. Average CTVs, ITVs and PTVs were 23.6 cc, 44.32 cc, 62.9 cc respectively; while the mean prescription isodose level and D2% were 76.5% and 31.2Gy, respectively. The plan conformity index and the GM were evaluated for all plans, reporting a median value of 1.15 (range 1-2.8), and 1.34 (respectively).