To use imaging data from stereotactic MR-guided online adaptive radiotherapy (SMART) of ultracentral lung tumors (ULT) for development of a safe non-adaptive approach towards stereotactic body radiotherapy (SBRT) of ULT. Analysis is based on 19 patients with ULT who received SMART (10 × 5.0–5.5 Gy) on a 0.35 T MR-Linac (MRIdian®) in the prospective MAGELLAN trial. 4D-planning CT data of six patients served to quantify proximal bronchial tree (PBT) breathing motion. Daily fraction MRIs are used to calculate interfractional translations (mediolateral (ML), anterior-posterior (AP), superior-inferior (SI)) and their dosimetric consequences for the PBT. A planning risk volume (PRV) is calculated for an assumed non-adaptive SBRT in deep-inspiration breath hold (DIBH) with surface-guidance (AlignRT®). Finally, non-adaptive volumetric modulated arc (VMAT) SBRT is simulated with and without a PRV for N = 10 patients (10 × 5.5 Gy). The PBT shows relevant breathing motion, especially in superior-inferior direction (median ML: 2.5 mm, AP: 1.9 mm and SI: 9.2 mm). Furthermore, moderate interfractional translations are observed (mean absolute translation ML: 1.3 mm, AP: 1.3 mm, SI: 1.1 mm), with an estimated 2 mm PRV margin for interfractional changes alone. Simulated non-adaptive SBRT leads to PBT overdoses in 60 % of patients (median overdosed fractions VMAT: 2.5, predicted MR-linac plans 4). Both MR-guided online plan adaptation (SMART) and PRV-based non-adaptive VMAT prevent PBT overdoses, but SMART yields significantly higher planning target volume (PTV) coverage (SMART: median 96 % [IQR 95–96], VMAT: median 89 % [IQR 77–94], p = 0.014). Both intrafractional breathing motion and interfractional translations may impact doses to the PBT during SBRT of ULT. SMART protects the PBT from overdoses while maintaining high PTV coverage. Non-adaptive SBRT appears safe with advanced breathing motion management and PRV, but yields inferior PTV coverage.

Background/Objectives: The implementation of tattoo-free radiotherapy (RT) for breast cancer reflects an effort to mitigate the psychological distress of permanent marks through surface-guided techniques, while simultaneously evaluating its utility in meeting setup precision requirements. Methods: In this prospective trial, patients were positioned for breast cancer RT including regional nodal irradiation exclusively using surface-guided RT (SGRT). Cone-beam computed tomography (CBCT) was acquired at each fraction as the ground truth to analyze translational setup deviations. Results: A total of 457 paired SGRT–CBCT data points in 30 patients were acquired. A residual translational setup deviation of ≤6 mm was achieved in 97.6% of all fractions with a median deviation of 2 mm (range: 0–12). Neither age, comorbidities, body mass index, extent of target volumes, choice of breathing technique, nor patient-reported symptoms (pain, dermatitis, anxiety) correlated significantly with setup deviations. The median in-room positioning time was 92 s (range: 20 s–6 min and 37 s) and significantly prolonged in patients with an elevated BMI and higher grades of pain and skin dermatitis, and for chest wall irradiation. Manual assessment of the accuracy of regional nodal CTVs in each CBCT relative to the planning CT showed good-to-minor deviations in 99.7% (Level 1/2), 95.0% (Supra-/infraclavicular), and 90.8% (Internal mammary), respectively, with major deviations in only 0.3% (Level 1/2), 5.0% (Supra-/infraclavicular) and 9.2% (Internal mammary). A forward dose calculation on CBCT geometries (n = 86) revealed high median CTV dose coverage of 100.0% (range: 57.1–107.7%) of the original target dose for all lymph node levels combined. Conclusions: The tattoo-free positioning setup for regional nodal irradiation in breast cancer patients exhibited pronounced robustness, maintaining its accuracy and reliability irrespective of patient-, tumor-, or treatment-specific variables with high clinical efficiency. However, larger cohorts are required to confirm whether these parameters genuinely operate independently of setup accuracy.

Whether FDG-PET–guided de-escalation of elective target volumes in radiotherapy of the head and neck reduces late toxicity remains uncertain. Therefore, we compared predicted toxicity of two de-escalation strategies—reduced elective nodal irradiation (RNI) and involved node irradiation (INI)—with standard elective nodal irradiation (ENI). In a within-patient plan comparison (n = 26), we generated RNI and INI plans using the same FDG-PET informed high-/intermediate-risk targets as ENI. RNI limited elective volumes to within 2 cm cranio-caudal from gross disease; INI omitted elective treatment. Proton plans were created in representative oropharyngeal cases. Co-primary outcomes were six-month normal-tissue complication probabilities (NTCPs) for dysphagia, feeding-tube dependence, and xerostomia. Median total planning target volume decreased from 540 cm³ (ENI) to 418 cm³ (RNI) and 173 cm³ (INI). RNI and INI reduced modeled dysphagia risk by 5.9 percentage points (pp) (95% CI 2.3 to 9.6 pp; p_adj = 0.005) and 11.0 pp (6.9 to 15.2 pp; p_adj < 0.001), feeding-tube dependence by 2.8 pp (1.2 to 4.5 pp; p_adj = 0.005) and 4.2 pp (2.5 to 6.0 pp; p_adj < 0.001), and xerostomia by 2.8 pp (0.0 to 5.7 pp; p_adj = 0.054) and 8.8 pp (5.5 to 12.2 pp; p_adj < 0.001), respectively. Predicted benefits were greatest in hypopharyngeal and laryngeal cancers. In selected cases, de-escalated proton therapy further reduced organ-at-risk dose. FDG-PET–guided volumetric de-escalation was associated with lower modeled late swallowing-related toxicity. These findings support the rationale for ongoing and future trials investigating volumetric de-escalation strategies.