ESTRO 2023 - Abstract Book

S1307

Digital Posters

ESTRO 2023

Conclusion SBRT offers a radical local treatment in selected patients. It is essential to standardize selection criteria of oligometastatis disease for an adequate indication of SBRT. More studies are needed, we are analysing more cases.

PO-1611 Paroxysmal atrial fibrillation in elderly: linac-based sbrt arrhythmia radioablation phase 2 trial

F. Gregucci 1 , A. Di Monaco 2 , I. Bonaparte 1 , A. Surgo 1 , R. Carbonara 1 , M.P. Ciliberti 1 , F. Di Guglielmo 1 , M. Caliandro 1 , E. Paulicelli 1 , E. Ludovico 3 , I. Romanazzi 2 , M. Grimaldi 2 , A. Fiorentino 1 1 Miulli General Regional Hospital, Radiation Oncology, Acquaviva delle Fonti, Italy; 2 Miulli General Regional Hospital, Cardiology, Acquaviva delle Fonti, Italy; 3 Miulli General Regional Hospital, Radiology, Acquaviva delle Fonti, Italy Purpose or Objective In elderly, paroxysmal atrial fibrillation (AF) is difficult to treat with drugs and catheter ablation due to the higher complication rate. Thus, non-invasive approaches should be favorite. STereotactic Arrhythmia Radioablation (STAR) was used for ventricular tachycardia, but no data are available for LINear ACcelerator (LINAC)-based STAR in AF patients. Based on this background, the primary and secondary endpoints of present prospective phase II trial are to evaluate, respectively, safety and efficacy of LINAC-based STAR for AF elderly patients. Here, clinical, dosimetric and planning data were reported. Materials and Methods The study was designed as a prospective phase-II trial started in May 2021, conducted in a single, referral center (ClinicalTrials.gov: NCT04575662). The inclusion criteria were: patients aged over 70 years, with symptomatic paroxysmal AF; intolerance or non-response to anti-arrhythmic (ATT) drugs. The primary study endpoint was the 1-month post-STAR safety, as complete STAR delivery and no acute treatment-related adverse events more than G3, assessed according to the Common Terminology Criteria for Adverse Events (version 5.0). Secondary endpoints were: reductions in AF episodes and in AAT, overall survival. The sample planning is 20 cases based on 95% success for the primary endpoint, with a significant level of 5% and a power of 90%. The date of the last follow-up was September 2022. The STAR treatment was performed in free breathing with a PTV prescription total dose of 25Gy in 1 fraction. Results Patient enrollment was closed in July 2022 with an accrual of 20/20 (100%), of these 18 patients were treated, 1 withdrew consent for treatment and 1 was excluded due to unfavorable anatomy. All patients completed STAR. No acute treatment related adverse events ( ≥ G2) at 1-month from procedure were registered. At a median follow up time of 7 months (range 12-2), 4 patients (25%) developed acute G1 esophagitis, resolved with local lenitive oral treatment and 2 patients (12%) reported a mild asymptomatic pericarditis to the 6-months control chest CT. In 1 patient, cardiac arrest occurred 15 minutes after the procedure, requiring cardiopulmonary resuscitation, without subsequent sequelae. No late side effects were reported. Eight patients, at 6-months from treatment, developed a relapse of AF, in the other 10 no AF episodes and no AAT use were reported. Mean 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 31.2 Gy, respectively. Regarding organ at risk, average heart and left anterior descending artery (LAD) Dmean were 3.9 and 6.3 Gy, respectively; while mean Dmax for LAD, spinal cord, left and right bronchus and esophagus were 11.2, 7.5, 14.3, 12.4 and 13.6 Gy respectively. The Overall Treatment Time (OTT) was 3minutes. Conclusion Clinical data suggest that LINAC-based STAR for AF could represent a valid non-invasive alternative therapy for elderly who were excluded from catheter ablation. 1 University College London Hospital, Radiotherapy, London, United Kingdom; 2 University College London Hospital, Radiotherapy Physics, London, United Kingdom Purpose or Objective Evaluate the inter and intrafraction motion of patients with bone oligometastasis from pre- and post-treatment CBCTs, to determine systematic and random sources of error that can be corrected and accounted for. Materials and Methods For oligometastatic bone patients the current IGRT strategy is a pre-treatment CBCT (online bone match), followed by a post-treatment CBCT to check for intrafraction motion. Bony oligometastasis are all treated with 3 fractions, using a 3mm CTV-PTV margin and are immobilised with long vacuum bags. This work was approved as a departmental evaluation to determine intrafraction motion for use in the Marcel Van Herk (MVH) margin calculation for hypo-fractionated data. The interfraction setup was also evaluated. The uncorrected pre-treatment CBCT shifts were used to calculate the group-wise mean [M] and systematic error [ ∑ ] to ensure M was small (< 1/3) compared to ∑ , or to indicate if any processes were causing systematic errors. The post treatment CBCT M, ∑ and random error [ σ ] were calculated. Again, M and ∑ were compared to ensure M was small (< 1/3) compared to ∑ . σ was recorded for use in margin calculation. Data were stratified to site and time to test for trends. Results 230 CBCTs (115 pre, 115 post) were retrospectively reviewed from 30 patients (37 treatment plans) treated from 2019 2020. Table 1 summarises the calculated M, ∑ and σ . The post-treatment results have been stratified into sites and image PO-1612 Inter and intrafraction motion in SABR patients treated for bone oligometastasis H. Hawes 1 , H. Grimes 2 , S. Moinuddin 1 , S. Petkar 1 , A. Webster 1