2001 - Worldwide Utilization of Stereotactic Ablative Radiotherapy for Early-Stage Non-Small Cell Lung Cancer: Are We All in Sync?

S. Alfaifi^1,2, A. V. Louie³, S. Siva⁴, M. Guckenberger⁵, G. M. Videtic⁶, K. Higgins⁷, F. Alshafa², H. AlGhamdi², E. F. Gillespie⁸, K. L. Stephans⁶, L. Mula-Hussain⁹, S. Harrow¹⁰, and D. A. Palma¹¹; ¹Cleveland Clinic, Cleveland, OH, ²King Faisal Medical City, Abha, Saudi Arabia, ³Sunnybrook Health Sciences Centre, University of Toronto, Toronto, ON, Canada, ⁴Peter MacCallum Cancer Centre, Melbourne, VIC, Australia, ⁵University Hospital of Zurich, University of Zurich, Zurich, Switzerland, ⁶Department of Radiation Oncology, Cleveland Clinic, Cleveland, OH, ⁷City of Hope Atlanta, Newnan, GA, ⁸University of Washington School of Medicine, Seattle, WA, ⁹Dalhousie University, Halifax, NS, Canada, ¹⁰Edinburgh Cancer Centre, Edinburgh, United Kingdom, ¹¹London Health Sciences Centre, London, ON, Canada

Purpose/Objective(s): This study aims to generate an understanding of the similarities and variations in international practice patterns for stereotactic ablative radiotherapy (SABR) in early-stage non-small cell lung cancer (NSCLC). Materials/

Methods: In this IRB approved study, an online survey was conducted from Oct to Dec 2023 covering general clinical and technical considerations for SABR, and common practice for 5 different anatomical NSCLC locations (table). Invitations to participate were extended through email and were distributed on social media platforms. ?² and ? tests were used. p <0.05 was significant.
Results: 255 radiation oncologists (one per institution) representing 51 countries across 6 continents completed the survey (North America (NA) 34%, Europe 32%, Asia 20%, South/Central America 7%, Oceania 5%, Africa 2%). Respondents reported treating a median of 20 NSCLC SABR patients per year. Across the 5 clinical scenarios, 58 different dose regimes were recommended. Utilization of a single fraction was significantly higher in NA centers in comparison to other regions (57% of practitioners vs. 29%, p<0.01). Two third of practices recommend BED_10Gy < 100 for one or more anatomical locations. Prescribing a BED_10Gy = 100 was significantly more frequent in NA centers for ultra-central (81% vs. 55%, p<0.01) and apical (93% vs. 82%, p=0.04) tumors. Heterogeneity corrections were used by 85% (99% in NA vs. 78% elsewhere, p=<0.01). An upper limit of the Dmax was used by 58% of participants, but this limit varied between different regions, with 86% of NA centers using upper Dmax limit at 130% Rx or higher vs. 49% of respondents elsewhere (p<0.01). The number of annual treated cases per participant was correlated with higher Dmax values (?=0.23, p<0.01). Conversely, a 120% Rx Dmax lower limit was used by 61% of NA centers vs. only 33% elsewhere (p<0.01). CI and R50 plan evaluation metrics were used by 65% and 56% of respondents, respectively, and they were more frequently used by NA practices (80% vs. 57% and 71% vs. 48% respectively; both p<0.01). PTV coverage was less frequently compromised in NA practices than other regions when chest wall dose exceed constraints for peripherally abutting chest wall tumors (19% vs. 48%, p<0.01).
Conclusion: Our findings demonstrate significant clinical variation in global SABR practice, particularly in dose selection, determining the desired level of plan heterogeneity “hotness" within the target, plan evaluation metrics, and PTV coverage. More data are needed to help inform prescription decisions, and international experts’ consensus may be beneficial to standardize practice. Abstract 2001 – Table 1

2 cm NSCLC; locations:	Most common dose	PTV coverage compromise*
Peripheral	54 Gy in 3 fx (40%)	51%
Peripheral abutting chest wall	50 Gy in 5 fx (25%)	38%
Central	50 Gy in 5 fx (47%)	87%
Ultra-central	60 Gy in 8 fx (41%)	97%
Apical	50 Gy in 5 fx (39%)	89%
* if OARs exceed constrains.