Planning on a static dataset that reflects the simulation day anatomy is routine for SBRT. We hypothesize the quality of on-table adaptive plans is similar to the baseline plan when delivering stereotactic MR-guided adaptive radiotherapy (SMART) for pancreatic cancer (PCa). Sixty-seven inoperable PCa patients were prescribed 50 Gy/5-fraction SMART. Baseline planning included: 3-5 mm gastrointestinal (GI) PRV, 50 Gy optimization target (PTV_opt) based on GI PRV, conformality rings, and contracted GTV to guide the hotspot. For each adaptation, GI anatomy was re-contoured, followed by re-optimization. Plan quality was evaluated for target coverage (TC = PTV_opt V_100%/volume), PTV D_90% and D_80%, homogeneity index (HI = PTV_opt D_2%/D_98%), prescription isodose/target volume (PITV), low-dose conformity (D_2cm = maximum dose at 2 cm from PTV_opt/Rx dose), and gradient index (R_50%=50% Rx isodose volume/PTV_opt volume).A novel global planning metric, termed the Pancreas Adaptive Radiotherapy Score (PARTS), was developed and implemented based on GI OAR sparing, PTV/GTV coverage, and conformality. Adaptive robustness (baseline to fraction 1) and stability (difference between two fractions with highest GI PRV variation) were quantified. OAR constraints were met on all baseline (n = 67) and adaptive (n = 318) plans. Coverage for baseline/adaptive plans was mean ± SD at 44.9 ± 5.8 Gy/44.3 ± 5.5 Gy (PTV D_80%), 50.1 ± 4.2 Gy/49.1 ± 4.7 Gy (PTV_opt D_80%), and 80%±18%/74%±18% (TC), respectively. Mean homogeneity and conformality for baseline/adaptive plans were 0.87 ± 0.25/0.81 ± 0.30 (PITV), 3.81 ± 1.87/3.87 ± 2.0 (R_50%), 1.53 ± 0.23/1.55 ± 0.23 (HI), and 58%±7%/59%±7% (D_2cm), respectively. PARTS was found to be a sensitive metric due to its additive influence of geometry changes on PARTS' sub-metrics. There were no statistical differences (p > 0.05) for stability, except for PARTS (p = 0.04, median difference -0.6%). Statistical differences for robustness when significant were small for most metrics (<2.0% median). Median adaptive re-optimizations were 2. We describe a 5-fraction ablative SMART planning approach for PCa that is robust and stable during on-table adaption, due to gradients controlled by a GI PRV technique and the use of rings. These findings are noteworthy given that daily interfraction anatomic GI OAR differences are routine, thus necessitating on-table adaptation. This work supports feasibility towards utilizing a patient-independent, template on-table adaptive approach.

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.

Purpose: While magnetic resonance-guided radiation therapy (MRgRT) may provide significant clinical advantages, delivery times tend to be longer than other radiation therapy (RT) modalities and published data on these times are limited. We evaluated longitudinal treatment times across our 8-year institutional MRgRT experience. Methods/Materials: A retrospective analysis of patients treated at our institution on a 0.35-Tesla MR-Linac between April 2018 and April 2026 was performed. All fractions were delivered with continuous intrafraction cine-MRI, soft tissue tracking, automatic beam gating, and online adaptive radiation therapy (oART) when indicated. The primary objective was to characterize changes in total in-room time (TIRT), treatment delivery time (TDT), and total adaptive time (TAT). For analysis of efficiency gains, our overall experience was separated into early (2018–2022) and late (2022–2026) periods. Results: A total of 1026 patients, 1203 treatment courses, and 7665 fractions were included. The median age was 69 years (range: 19–94) and the most commonly treated sites by treatment course were pancreas (n = 430; 35.7%), thorax (n = 203; 16.9%), abdominopelvic lymph nodes (n = 181; 15.0%), liver (n = 138; 11.5%), and adrenal gland (n = 83; 6.9%). The median prescription dose was 50 Gy (range: 16.0–76.0) in a median of five fractions (range: 1–36). Breath-hold and stereotactic body radiation therapy (SBRT) were used in 87.9% and 88.5% of treatment courses, respectively. From the early (2018–2022) to late (2022–2026) study period, the proportion of fractions utilizing SBRT (49.9% vs. 81.1%; p < 0.001), oART (32.9% vs. 80.2%; p < 0.001), respiratory gating (75.9% vs. 88.8%; p < 0.001), and elective nodal coverage (61.8% vs. 78.2%; p < 0.001) increased, as did the proportion of pancreatic treatments (20.4% vs. 38.4%; p < 0.001) and the utilization of single-fraction courses (3.4% vs. 10.3%; p < 0.001). Despite this increasing complexity between study periods, median oART TIRT decreased from 67.0 to 48.0 min (28.4% reduction; p < 0.001), driven primarily by a reduction in TAT from 20.0 to 7.0 min, p < 0.001. Pancreatic oART fractions showed the greatest improvement (median TIRT, 70.0 to 47.0 min; p < 0.001). In 2022–2026, 78.1% of oART fractions were completed within 60 min vs. 35.5% in 2018–2022 (p < 0.001). Conclusions: Ablative MRgRT, with or without oART, can often be delivered in 60 min or less, including for mobile and anatomically unfavorable tumors. Future software and hardware advances are expected to further improve MRgRT treatment efficiency.

Total body irradiation (TBI) is used with chemotherapy to induce immunosuppression for hematopoietic cell transplantation and is often administered using lead blocks to minimize lung dose in adults and children. This technique is challenging in infants and young children. A 13-month-old female with acute lymphoblastic leukemia (ALL) was treated with fractionated TBI to a dose of 12 Gy in eight fractions delivered twice daily. Multiple TBI techniques for delivering treatment were considered. Ultimately, treatment using helical tomotherapy was selected in order to spare and accurately quantify the dose to the lung, meet lung dose constraints, and ensure adequate TBI dose coverage. With anesthesia, this technique provided a comfortable and reproducible set-up for the young child. The treatment plan was delivered with intensity-modulated radiotherapy, where 96.4% of the target volume received a prescription dose with a total beam-on time of 16.8 minutes. The mean lung dose was 7.7 Gy for a total lung volume of 245cc. This report describes the challenges faced during the treatment planning and delivery, and how they were resolved.