Background/Objectives: Over the past decade, significant advances have been made in image-guided radiotherapy (RT) particularly with the introduction of magnetic resonance (MR)-guided radiotherapy (MRgRT). However, the optimal clinical applications of MRgRT are still evolving. The intent of this analysis was to describe our institutional MRgRT utilization patterns and evolution therein, specifically as an early adopter within a center endowed with multiple other technology platforms.Materials/Methods:We retrospectively evaluated patterns of MRgRT utilization for patients treated with a 0.35-Tesla MR-Linac at our institution from April 2018 to April 2024. We analyzed changes in utilization across six annualized periods: Period 1 (April 2018–April 2019) through Period 6 (April 2023–April 2024). We defined ultra-hypofractionation (UHfx) as 5 or fewer fractions with a minimum fractional dose of 5 Gy. Electronic health records were reviewed, and data were extracted related to patient, tumor, and treatment characteristics.Results: A total of 823 treatment courses were delivered to 712 patients treated for 854 lesions. The most commonly treated sites were the pancreas (242 [29.4%]), thorax (172; 20.9%), abdominopelvic lymph nodes (107; 13.0%), liver (72; 8.7%), and adrenal glands (68; 8.3%). The median total prescribed dose of 50 Gy in five fractions (fxs) was typically delivered in consecutive days with automatic beam gating in inspiration breath hold. The median biologically effective dose (α/β = 10, BED10) was 94.4 Gy with nearly half (404, 49.1%) of all courses at a prescribed BED10 ≥ 100 Gy, which is widely regarded as a highly effective ablative dose. Courses in Period 6 vs. Period 1 more often had a prescribed BED10 ≥ 100 Gy (60.2% vs. 41.6%;p= 0.004). Of the 6036 total delivered fxs, nearly half (2643, 43.8%) required at least one fx of on-table adaptive radiotherapy (oART), most commonly for pancreatic tumors (1081, 17.9%). UHfx was used in over three quarters of all courses (630, 76.5%) with 472 (57.4%) of these requiring oART for at least one fraction. The relative utilization of oART increased significantly from Period 1 to Period 6 (37.6% to 85.0%;p< 0.001); a similar increase in the use of UHfx (66.3% to 89.5%;p< 0.001) was also observed. The median total in-room time for oART decreased from 81 min in Period 1 to 45 min in Period 6, while for non-oART, it remained stable around 40 min across all periods.Conclusions: Our institution implemented MRgRT with a priority for targeting mobile extracranial tumors in challenging anatomic locations that are frequently treated with dose escalation, require enhanced soft-tissue visualization, and could benefit from an ablative radiotherapy approach. Over the period under evaluation, the use of high-dose ablative doses (BED10 ≥ 100 Gy), oART and UHfx (including single-fraction ablation) increased significantly, underscoring both a swift learning curve and ability to optimize processes to maximize throughput and efficiency.
背景/目的：过去十年间，图像引导放射治疗（RT）领域取得显著进展，尤其是磁共振引导放射治疗（MRgRT）技术的引入。然而，MRgRT的最佳临床应用模式仍在持续探索中。本研究旨在描述我院作为早期应用单位（同时配备多种其他技术平台）的MRgRT临床应用模式及其演变过程。 材料/方法：我们回顾性分析了2018年4月至2024年4月期间在我院0.35特斯拉MR-Linac系统接受治疗患者的MRgRT应用模式。将研究时段划分为六个年度周期（周期1：2018年4月-2019年4月；周期6：2023年4月-2024年4月）进行分析。定义超大分割（UHfx）为≤5次分割且单次剂量≥5 Gy的治疗方案。通过电子健康记录提取患者、肿瘤及治疗特征相关数据。 结果：共对712名患者的854个病灶实施823个治疗疗程。最常见治疗部位包括胰腺（242例，29.4%）、胸部（172例，20.9%）、腹盆腔淋巴结（107例，13.0%）、肝脏（72例，8.7%）和肾上腺（68例，8.3%）。中位处方总剂量为50 Gy/5次分割，通常在连续治疗日内通过吸气屏气自动门控技术实施。中位生物有效剂量（α/β=10，BED10）为94.4 Gy，近半数疗程（404例，49.1%）处方BED10≥100 Gy（该剂量被广泛认为是高效消融剂量）。与周期1相比，周期6中处方BED10≥100 Gy的疗程比例显著增加（60.2% vs 41.6%；p=0.004）。在全部6036次分割治疗中，近半数（2643次，43.8%）需要至少一次在线自适应放疗（oART），其中胰腺肿瘤占比最高（1081次，17.9%）。超过四分之三的疗程（630例，76.5%）采用UHfx方案，其中472例（57.4%）需要至少一次oART。从周期1到周期6，oART的相对使用率显著提升（37.6%至85.0%；p<0.001），UHfx使用率也呈现相似增长趋势（66.3%至89.5%；p<0.001）。oART治疗的中位室内总时间从周期1的81分钟缩短至周期6的45分钟，而非oART治疗在各周期均稳定维持在40分钟左右。 结论：我院实施MRgRT时优先选择治疗具有挑战性的颅外活动性肿瘤，这些肿瘤常需剂量递增、依赖优质软组织显像，且可能从消融性放疗中获益。评估期间，高剂量消融（BED10≥100 Gy）、oART及UHfx（包括单次消融）的应用显著增加，这既体现了快速的学习曲线，也证明了优化流程以提升治疗通量和效率的能力。
肿瘤(癌症)患者之家