Background and purpose In the combined treatment of osteosarcoma with a carbon ion radiotherapy (CIRT) boost, large pelvic tumors are associated with significantly lower tumor control compared to craniofacial localization. This could be linked to lower dose-averaged linear energy transfer (LETd) values in the target and larger uncertainties related to the model used for relative biological effectiveness (RBE) calculation. This study aimed to bridge the difference between RBE-weighted doses from two clinically used models, the local effect model I (LEM-I) and the modified microdosimetric kinetic model (mMKM), using LETd optimization. Materials and methods Fifteen pelvic osteosarcoma CIRT plans, initially optimized with LEM-I, were re-optimized to achieve higher target LETd while preserving target and organ at risk (OAR) dose objectives. Both dose- and LET-optimized plans were recalculated with mMKM, and dose metrics were compared across the groups. Robustness against setup and range uncertainties and changes in patient anatomy (using control CTs) was investigated. Results LETd optimization resulted in target LETd escalation without compromising LEM-I target coverage. The LET-optimized group also demonstrated better mMKM dose coverage and a significant decrease (up to 9% of prescription) in the disparity between LEM-I and mMKM target dose. OAR doses remained largely unaffected by model choice or optimization strategy. The robustness loss with LETd optimization was minor (intra-patient dose variability increased by 0.3–2.3%) compared to the reduction in model-to-model variation. Conclusions When adequately balanced with physical uncertainties, LETd optimization could become a useful strategy for bridging RBE model predictions and increasing the efficacy of CIRT.
Ozcan and colleagues present an exploratory radiomic analysis of 24 surgically treated patients with pathologically confirmed mandibular osteoradionecrosis (ORN), including three with associated recurrence (Ozcan et al., 2026 [1]). While the clinical question is important, the validity of the underlying reference standard requires careful scrutiny before interpreting radiomic differences as indicators of recurrence within ORN.
Background and Purpose Magnetic resonance-guided radiotherapy systems require comprehensive quality assurance (QA) programs to ensure safe and precise treatment delivery. This study evaluates the long-term behavior and variability of linac-related QA results across three clinically operated 1.5 T MRI-linacs at a single institution and assesses compliance with tolerance limits. Materials and Methods QA data acquired over a six-year period from three clinically operated 1.5 T MRI-linacs were retrospectively analyzed. A range of linac-related dosimetric and mechanical QA tests was included. Performance envelopes (mean ± 2 SD) were constructed to characterize variability relative to tolerance limits. Results For 11 of 13 QA tests, performance envelopes for the associated metrics remained within the applied tolerance limits. For the two remaining tests, envelopes slightly extended beyond these limits. These deviations were not considered clinically relevant, and their underlying causes were understood. No progressive trends of clinical relevance were observed in the linac-specific time series. Conclusions Stability of linac-related QA results was demonstrated over six years across three MRI-linacs, supporting reconsideration of the QA program.
