International Journal of Radiation Oncology*Biology*Physics

Purpose: Elective nodal (EN) irradiation (ENI) during radiotherapy for locally advanced head-and-neck squamous cell carcinoma (LA-HNSCC) influences hematotoxicity, anti-tumor immunity, and synergy with immunotherapy. We evaluated whether EN-sparing upfront boosts affect DNA damage, systemic immune signaling in peripheral blood lymphocytes (PBLs), and radiation-induced lymphopenia (RIL). Methods and Materials: Twenty-eight patients with LA-HNSCC were randomized to either adjuvant or definitive chemoradiotherapy with standard ENI or EN-sparing upfront boost (adjuvant: 2x2 Gy; definitive: 5x2 Gy). Blood was collected pre-radiotherapy, 15 min, and 24 h after the first fraction, and before the sixth fraction. DNA damage in PBLs was assessed via {gamma}H2AX and 53BP1 foci and dicentric chromosome (DIC) assay. RNA sequencing was performed in two patients per group (definitive setting) at pre-CRT, before the sixth fraction, and at therapy end. Absolute lymphocyte counts (ALCs) were monitored weekly to assess RIL. Results: DNA damage in PBLs correlated with planning target volume and whole-body dose, both of which were reduced by EN-sparing by 9.9-fold and 4.4-fold, respectively (p < 0.001 each). Correspondingly, EN-sparing significantly reduced radiation-induced foci and DIC levels in PBLs (3-4-fold, p < 0.001) and lowered the fraction of radiation-damaged PBLs per fraction (11% vs. 23% with ENI, p < 0.001). EN-sparing preserved baseline ALCs during week 1 of chemoradiotherapy and delayed RIL, whereas ENI caused an immediate ALC decline and RIL. Lymphocyte counts after week 1 negatively correlated with planning target volume, whole-body dose, and DNA damage in PBLs (p < 0.01). Transcriptomics showed metabolic and interferon signaling associated with EN-sparing, versus sterile inflammatory and damage-associated patterns with ENI. Conclusions: EN-sparing by an upfront boost significantly reduced PBL damage and early RIL with distinct immune responses associated with lymphocyte viability and immune maturation. These findings support upfront EN-sparing strategies to mitigate RIL and improve radiotherapy-immunotherapy synergy in HNSCC.

PurposeRecurrence in high-grade glioma (HGG) predominantly occurs within the high-dose radiation field, raising the question of whether treatment failure reflects limitations in radiation target delineation or is driven by intrinsic tumor biology. This study evaluated recurrence patterns following standard chemoradiotherapy and their treatment implications. Material and MethodsThis retrospective single-center study included 41 patients with histologically confirmed HGG treated with surgery followed by radiotherapy with concurrent and adjuvant temozolomide (TMZ). Patients were followed through August 2018; those with recurrence were included in the analysis. Recurrence patterns were classified based on their spatial relationship to the 60 Gy isodose line as central, in-field, marginal, or distant. Survival outcomes were estimated using the Kaplan-Meier method and compared using the log-rank test. ResultsThe most common pattern of recurrence was central (15 patients, 36.5%), followed by in-field (11, 26.8%), distant (6, 14.6%), marginal (5, 12.1%), and multicentric (4, 9.8%). Central and in-field recurrences (local failures) accounted for 26 patients (63%). Median overall survival (OS) was 27 months, and median progression-free survival (PFS) was 12 months. Survival differed significantly by recurrence pattern (log-rank p = 0.018), with marginal recurrence associated with more favorable outcomes. ConclusionThe predominance of central and in-field recurrences within the high-dose region suggests that treatment failure in HGG is not solely explained by inadequate target delineation and may also be driven, in part, by intrinsic tumor biology, including radioresistant subpopulations and tumor heterogeneity. Future strategies may benefit from incorporating biologically guided approaches alongside optimization of radiation treatment parameters.

Background: Reirradiation (reRT) is increasingly offered following progression in diffuse intrinsic pontine glioma (DIPG) and diffuse midline glioma (DMG), though optimal patient selection remains a challenge. This study evaluated clinical outcomes after reRT in a contemporary cohort of patients with DIPG/DMG. Methods: Patients <26 years old with DMG/DIPG treated with radiation therapy between 2011-2025 were retrospectively reviewed. Primary endpoints included overall survival (OS2) and progression-free survival (PFS2), measured from first progression, and change in neurologic symptoms after reRT. Survival was estimated using Kaplan Meier methods, with Cox proportional hazards modeling for prognostic factors. Results: Fifty eight patients were included; 37 (63.8%) underwent reRT. Tumors were predominantly pontine (74.1%). ReRT was associated with improvement in motor function (51.4% vs. 9.5%, p=0.002), cranial nerve function (29.7% vs. 4.8%, p=0.044), and gait ataxia (35.1% vs. 9.5%, p=0.059). Median OS2 and PFS2 were improved with reRT (OS2: 9.67 vs. 2.57 months, p<0.001; PFS2: 5.63 vs. 1.57 months, p<0.001). OS2 was independently associated with reRT (HR 0.27, p<0.0001), pontine location (HR 2.94, p=0.004), and steroid use at progression (HR 4.12, p=0.001). PFS2 was independently associated with reRT (HR 0.23, p < .0001) and distant pattern of failure (HR 2.83, p=.037). Among reRT patients, non-pontine location was associated with improved OS2 (p=0.02), and local failure was associated with improved PFS2 (p=0.003). Conclusion: ReRT was associated with neurologic improvement and prolonged survival. Patients with non-pontine tumors or local-only failure might derive the greatest benefit. Prospective studies are warranted to define optimal dose/fractionation and refine patient selection.

Purpose: Manual verification of AI-based auto-contouring is labor-intensive and prone to fatigue-related errors. This study developed the large language model (LLM)-based automated Quality Assurance (QA) for auto-contouring (LAQUA) system using a multimodal LLM, Gemini 2.5 Pro, and evaluated its feasibility as a clinical primary screening tool to streamline the QA workflow. Methods: Twenty male pelvic CT scans from an open dataset were utilized. Three distinct auto-contouring software packages (OncoStudio, RatoGuide prototype and syngo.via) were evaluated. Auto-contouring results for each slice were exported as PDF images with overlaid contours and input into Gemini 2.5 Pro. The LLM was instructed to rate the contour quality on a 5-point clinical scale (5: Optimal; 4: Acceptable; 3: Suboptimal; 2: Unacceptable; redraw from scratch; 1: Unacceptable; organ not detected). Using evaluations by two board-certified radiation oncologists as ground truth, Spearman's rank correlation coefficients ({rho}) and weighted kappa coefficients ({kappa}) were calculated. Additionally, to assess screening performance, sensitivity and specificity were calculated by dichotomizing the scores into "Pass" and "Fail" using two different cutoffs (scores [&ge;] 3 and [&ge;] 4 as "Pass"). Finally, the alignment of the rationales provided by the LLM with the auto-contouring quality was evaluated by two board-certified radiation oncologists. This was conducted using a Likert scale assessing four domains (error detection, hallucination, clinical relevance, and anatomical understanding), each scored out of 2 points. Results: The LAQUA system demonstrated moderate to strong agreement with expert judgments across all evaluated organs ({rho}: 0.567 - 0.835; quadratic weighted {kappa} : 0.639 - 0.804), with the rectum showing the highest correlation. Regarding screening performance, a cutoff of [&ge;]3 as "Pass" achieved the highest sensitivity and specificity in specific subgroups, but with wide 95% confidence intervals (CIs). A cutoff of [&ge;]4 as "Pass" narrowed the CIs, yielding the highest sensitivity in the rectum (0.976) and the highest specificity in the left femoral head (0.933). Qualitatively, the LLM's rationales achieved an overall mean score of 1.70 {+/-} 0.48 (out of 2), with 155 of 291 outputs receiving perfect scores across all criteria. Conclusions: The LAQUA system demonstrated substantial agreement with expert evaluations in AI-based auto-contouring quality assessment. While potential overestimation bias (risk of missing "Fail" cases) warrants caution, the observed sensitivity suggests its feasibility as a primary screening QA tool to efficiently filter acceptable contours, thereby reducing the clinical workload.

Clinical studies of prostate cancer treated with radically hypofractionated highdose-rate brachytherapy (HDR-BT) have reported a significant loss of tumor control that contradicts the standard linear-quadratic (LQ) and low /{beta} ratio paradigm for prostate cancer. In a previous study by our group, we showed that the linear-quadraticlinear (LQL) model could describe this response, but the underlying biological drivers remained unclear. In this follow-up study, we further investigate whether the interplay between hypoxia and reoxygenation kinetics can explain the poor response to extreme hypofractionation. We analyzed a large dataset of 3,239 patients (44 schedules) using a three-compartment reoxygenation model (the MSK model) that simulates the dynamics of oxic, intermediate, and hypoxic cell populations. Results show that the MSK model achieves an excellent fit to the clinical data (p > 0.99) while maintaining a biologically plausible low /{beta} ratio ([&le;] 8 Gy). The reoxygenation model provided a performance comparable to the LQL model for low-risk prostate cancer, being slightly inferior to the LQL model to describe the response of intermediate-risk. This suggests that the observed reduction in tumor control is not necessarily a failure of the LQ formalism, but rather a consequence of oxygen dynamics associated with ultra-fractionated schedules, and provides a mechanistic basis for designing clinical trials exploring the response of prostate cancer to ultra-hypofractionation and the role of reoxygenation.

Background Cardiovascular adverse events (CVAEs) after chemoradiotherapy (CRT) for lung cancer are major concerns in Appalachia due to high rates of smoking and pre-existing cardiovascular diseases (CVD). The objectives of this study were to characterize the incidence of CVAEs in this population and evaluate machine learning (ML) models for CVAEs risk stratification and mortality prediction. Methods A retrospective study was conducted among Appalachian patients with lung cancer treated with definitive CRT at a single institution between 2013 and 2025. Baseline clinical variables, including demographics, smoking status, pre-existing CVD, and post-CRT CVAEs were collected. Heart dosimetric parameters were also obtained. ML models [Random Forest (RF), Gradient Boosting (GBM), Support Vector Machine (SVM), Logistic Regression (LR)] were trained using 5 fold cross validation and evaluated using AUC, sensitivity, specificity, and F1 score. Feature importance was assessed using permutation analysis. Wilcoxon and Chi-squared tests were used for descriptive comparisons. Results Eighty-six patients (mean age 66 years, 47% male) were included. At diagnosis, 80% (n=69) had NSCLC and 20% (n=17) had LS-SCLC. CVAEs occurred in 51 patients (59%). The most frequent events were NSTEMI (n=15, 29.4%), pericardial disease (n=15, 29.4%), and arrhythmia (n=8, 15.7%). Mean heart dose was higher in the CVAE group (13.4 vs 9.4 Gy, p=0.27). For CVAE prediction, GBM achieved the highest AUC (0.55, 95% CI 0.44-0.69) and sensitivity (75%), while RF showed the highest sensitivity (80%, 95% CI 69-90%). Key predictors included age and cardiac dosimetrists (Heart V20, V40, V50, and mean heart dose). For mortality prediction, RF achieved the highest discrimination (AUC = 0.63, 95% CI 0.496-0.750). Age, cardiac dosimetry, disease stage, and cardiovascular comorbidity were the most influential predictors. Conclusion High incidence of CVAEs occurred among patients with lung cancer treated with CRT in this Appalachian cohort. While ML models demonstrated modest predictive performance, tree-based approaches demonstrated high sensitivity for identifying patients at risk for CVAEs and mortality. Age and cardiac radiation dose metrics consistently emerged as key predictors, highlighting the importance of cardiac dose optimization and ML-based risk stratification for cardio-oncology surveillance.

BACKGROUNDSubcutaneous white adipose tissue (scWAT), a key metabolic and endocrine organ, is inevitably exposed during radiotherapy (RT). While RT is a cornerstone of cancer treatment, its efficacy is limited by toxicity to surrounding healthy tissues. Ultra-high dose rate (FLASH) RT has emerged as a promising modality capable of preserving tumor control while reducing normal tissue damage - the so-called FLASH effect. Clinical evidence indicates that childhood exposure to conventional (CONV) RT is associated with long-term dysmetabolism and WAT dysfunction. However, the impact of FLASH-RT on WAT has not been investigated. AIMTo compare the effects of FLASH- and CONV-RT on adipocyte function and scWAT homeostasis, and to identify molecular and structural changes associated with each modality. METHODSWe evaluated the effects of FLASH- and CONV-RT on adipocytes and scWAT using a dedicated linear accelerator capable of delivering both modalities. Experiments were performed in the human SGBS preadipocyte/adipocyte cell line and in a mouse model subjected to proximal hind limb irradiation, with analyses conducted 70 days post-exposure. RESULTSRT impaired adipogenic differentiation in a dose-dependent manner, with a relative sparing effect of FLASH at 4-8 Gy. Mature adipocytes exhibited radioresistance, with protection by FLASH at 8 Gy. In vivo, both regimens reduced fat mass without affecting body weight, with greater loss following CONV-RT. Transcriptomic profiling of scWAT revealed inflammatory and neurodegenerative signatures after CONV-RT, whereas FLASH-RT induced minimal transcriptional changes. Histological and ultrastructural analyses confirmed increased cellular damage, vacuolization, lipid spill-over, and reduced PLIN1 expression, predominantly in CONV-treated mice. CONCLUSIONSWAT homeostasis is sensitive to conventional RT, whereas FLASH-RT better preserves tissue structure and function, with implications for long-term metabolic health in cancer survivors.

PurposeGlioblastoma (GBM) is characterized by poor clinical outcomes and marked resistance to radiotherapy. Because effective radiosensitizing strategies for GBM remain limited, we investigated whether inhibition of KRAS/RAS signaling could enhance radiation response in GBM. In particular, we evaluated the radiosensitizing potential of RMC-6236, an RAS(ON) multiselective inhibitor that suppresses active RAS signaling across multiple RAS-dependent states. Experimental DesignHuman GBM cell lines (U251, LN-18, ACPK1, and OSU61) were treated with radiation, with or without genetic or pharmacological KRAS inhibition. KRAS signaling was suppressed by siRNA-mediated knockdown or RMC-6236 treatment. Radiation-induced KRAS activation and downstream MAPK signaling were assessed by Raf-RBD pull-down assays and immunoblotting. Radiosensitivity was evaluated using clonogenic survival assay. DNA damage persistence, cell cycle distribution, and mitotic catastrophe were analyzed by {gamma}H2AX immunofluorescence, flow cytometry, and nuclear morphology assessment, respectively. In vivo therapeutic efficacy was examined in an orthotopic U251 xenograft model. ResultsRadiation-induced transient activation and increased KRAS protein expression of KRAS, accompanied by activation of ERK, JNK, and p38 signaling in GBM cells. siKRAS suppressed radiation-induced KRAS and MAPK activation, and significantly enhanced radiosensitivity in all four GBM cell lines. Similarly, RMC-6236 inhibited radiation-induced KRAS activation and attenuated downstream MAPK signaling without reducing the total KRAS protein expression. RMC-6236 significantly increased the radiosensitivity across all GBM cell lines, with dose enhancement factors ranging from 1.33 1.46. Mechanistically, combined treatment with RMC-6236 and radiation increased persistent {gamma}H2AX foci and enhanced mitotic catastrophe without producing consistent redistribution of cells into radiosensitive cell cycle phases. In an orthotopic GBM model, the combination of RMC-6236 and radiation significantly prolonged survival compared to that of the control and radiation alone. ConclusionsThese findings indicate that radiation-induced KRAS signaling is a functionally important mediator of radioresistance in GBM and demonstrate that inhibition of KRAS/RAS signaling enhances the radiation response in vitro and in vivo. RMC-6236 may represent a promising radiosensitizing strategy for GBM by suppressing adaptive RAS/MAPK signaling and promoting persistent DNA damage and mitotic catastrophe following irradiation. However, clinical trials of this combination are warranted.

It has been hypothesized that effective cellular internalization is required for the retention of 225Ac daughter radionuclides. The complex decay chain of 225Ac and recoil-mediated release of daughters, particularly 213Bi (half-life (t1/2) = 46 min), raise concerns about redistribution that may reduce tumor absorbed dose (TAD) and increase off-target radiation exposure. Because somatostatin receptor subtype 2 (SSTR2) antagonists such as SSO110 are not internalized, it has been proposed that the daughter radionuclides are less effectively retained compared to internalizing agonists such as DOTA-TATE. We therefore performed a direct and quantitative comparison of daughter radionuclide redistribution following administration of [225Ac]Ac-SSO110 and [225Ac]Ac-DOTA-TATE. MethodsBiodistribution and 213Bi redistribution were evaluated in Balb/c nude mice bearing NCI-H69 small cell lung cancer xenografts. Repeated gamma counting combined with bi-exponential modeling was used to quantify 225Ac and 213Bi activity in tumor, blood, bone marrow, kidneys, liver, and intestines up to 96 h post-injection. TAD was calculated with and without accounting for experimentally-derived 213Bi redistribution. Real-time in vitro binding assays were conducted to characterize cellular retention of [225Ac]Ac-SSO110. Results[225Ac]Ac-SSO110 demonstrated higher tumor uptake and prolonged retention compared with [225Ac]Ac-DOTA-TATE, resulting in a 1.9-fold higher tumor-to-kidney ratio at 96 h and a 2.8-fold higher TAD. Redistribution of 213Bi from tumor was minimal and comparable between agonist and antagonist, with maximum tumor loss of 3.5% for [225Ac]Ac-SSO110 and 2% for [225Ac]Ac-DOTA-TATE. Accounting for daughter redistribution reduced TAD by less than 5% for both radioconjugates. No sustained 213Bi accumulation was observed in blood, kidneys, or liver, and only minimal activity was detected in bone marrow and intestines. Real-time binding studies demonstrated sustained cell-associated {beta}- signal following incubation with [225Ac]Ac-SSO110. ConclusionReceptor-mediated internalization is not required for effective retention of 225Ac daughter radionuclides. Despite negligible internalization, [225Ac]Ac-SSO110 achieved superior TAD and higher tumor-to-kidney ratio without increased daughter redistribution compared with the internalizing agonist [225Ac]Ac-DOTA-TATE. These findings question the necessity of internalization for daughter retention and support further evaluation of antagonist-based 225Ac radioligand therapy.

Humanized mice (hu-mice), which recapitulate the human immune system, have become increasingly important for preclinical immunotherapy studies. Among these models, the human peripheral blood mononuclear cells (PBMC)-engrafted hu-mice model is the simplest and fastest. However, its utility is hindered by the development of lethal graft-versus-host disease (GvHD) and the insufficient reconstitution of human leukocytes. To address these limitations, we developed PBMC hu-mice models using a novel strain, NOD-CD47nullRag2nullIL-2r{gamma}null (RTKO) focusing on the immunological defects of the NOD strain and the immunotolerance provided by CD47 deficiency. Six-week-old female NOD-Rag2nullIL-2r{gamma}null (RID) and RTKO mice were intravenously injected with three different PBMC doses (3x106, 5x106, and 1x107 cells). At standard doses (5x106 and 1x107 cells), RTKO mice exhibited enhanced engraftment of human leukocytes, though GvHD was more severe compared to the RID strain, resulting in a limited experimental window. However, in a subsequent trial using a lower dose of PBMCs (3 x 106 cells), RTKO mice demonstrated notable advantages, including stable reconstitution of human leukocytes, milder GvHD symptoms without life-threatening lesions, and a markedly prolonged experimental window. Considering the difficulties in generating hematopoietic stem cell (HSC)-engrafted hu-mice, the extended experimental window provided by this model, which is comparable to HSC hu-mice, is a significant improvement. Moreover, the radiation tolerance conferred by the Rag gene mutation in this model offers another advantage for radiotherapy research. Consequently, the low-dose PBMC RTKO model serves as a versatile and valuable platform for a broad spectrum of immunotherapy studies, especially in the field of immuno-oncology.

Patients with Fanconi anemia (FA) are particularly susceptible to developing squamous cell carcinoma of the head and neck due to impaired DNA repair pathways. However, their hypersensitivity to DNA damaging agents can limit effective treatment with standard radiotherapy due to severe side effects and complications. In pre-clinical models, ultra-rapid FLASH radiotherapy (FLASH) reduces radiation-induced toxicity in normal tissues while maintaining similar tumor control compared to conventional dose rate radiotherapy (CONV). Here, we investigated the safety of FLASH for treatment of the head and neck in a mouse model of FA. 129/Sv wild-type (WT) and Fanca-deficient (Fanca-/-) mice received single-dose oral cavity irradiation with electron beam FLASH or CONV to evaluate radiation-induced toxicity in non-tumor-bearing mice. Fanca WT and Fanca-/- mice were irradiated with 25 and 18 Gy, respectively, of FLASH (190 Gy/sec) or CONV (0.2 Gy/sec), with tongues harvested at 12 hours (hpi) and 10 days (dpi) post-irradiation. At 10 dpi, FLASH-irradiated tongues in both genetic backgrounds demonstrated reduced ulceration at the dorsal tongue surface compared to CONV-irradiated counterparts. Histopathological analysis of the tongue revealed lower mucositis severity scores with decreased epithelial thinning and ulceration in FLASH-irradiated tongues compared to CONV-irradiated ones. Analysis of {gamma}-H2AX foci formation at 12 hpi demonstrated fewer foci in WT mice treated with FLASH compared to CONV, with a similar trend observed in Fanca-/- mice. These findings suggest a potential normal tissue-sparing effect with FLASH and hold important clinical implications for the treatment of patients with Fanconi anemia and head and neck cancers.

Our study evaluated whether a deep learning auto segmentation model combined with machine learning triage can streamline radiotherapy clinical trial quality assurance (QA). We analyzed 107 stereotactic ablative radiotherapy (SABR) cases from a multi-institutional phase II clinical trial of neurovascular sparing prostate SABR, focusing on physician contours of the internal pudendal artery (IPA) as a novel organ-at-risk with substantial interobserver variability. Contours were scored by the trial principal investigator as Per-Protocol or Minor Deviation/Unacceptable. We applied a deep learning model for IPA auto-segmentation. Agreement between human and AI contours was then quantified using 14 overlap, distance, and surface metrics, and a supervised classifier was trained on these metrics to flag clinical trial protocol deviations. While AI segmentation achieved only modest geometric accuracy with mean Dice similarity coefficient of 0.446 and 95th percentile Hausdorff distance of 14.23, when incorporating all 14 metrics, a machine learning classifier yielded AUROC of 0.836, flagging all Minor Deviation/Unacceptable cases with 100% sensitivity on the 27 case hold-out set with 6 false positives and no false negatives. AI segmentation combined with metrics-based machine learning can triage protocol deviations within a multi-institution radiotherapy clinical trial, supporting prospective evaluation of AI-assisted trial QA.

BackgroundFLASH-RT defines a promising treatment modality against medulloblastoma, as it minimizes treatment-related complications. To support its clinical translation, we dissected the cellular and molecular determinants of the FLASH response in the tumor-microenvironment (TME) and healthy hippocampus using an orthotopic human medulloblastoma mouse model treated with a hypo-fractionated FLASH regimen. MethodsFive cohorts of 4 weeks-old UW228-MB-bearing female nude mice (n=57) were irradiated, or sham-irradiated using 3x10 Gy (BED=60), delivered 48h apart at 0.1 Gy/s (CONV) or 5.5x106 Gy/s (FLASH) using an electron beam (eRT6). Digital spatial profiling (DSP) was performed 24h after radiotherapy in one cohort, while the four other cohorts were followed for long-term tumor response, cognition, and neuroinflammation. ResultsBoth CONV and FLASH-RT induced a complete and long-lasting anti-tumor response in 100% of animals associated with cognitive decline. However, more mice maintained a very good discrimination score after FLASH exposure (38%) than CONV (7%). DSP revealed a sustained microglial activation in the cerebellar tumor micro-environment, where FLASH enhanced expression of genes with phagocytic and proteolytic activity. In the tumor free hippocampus, FLASH exposure induced a preferential neuron/astrocyte transcriptional crosstalk, which manifested over protracted times to minimize neuroinflammation and cognitive complications. ConclusionThe study shows the tumor-ablative efficacy of hypo-fractionated FLASH-RT in a human medulloblastoma mouse model. It is associated with qualitatively distinct transcriptional signatures prone to tumor and debris clearance mediated by microglial cells of the TME. Moreover, in the hippocampus, FLASH mitigates radiation-induced neurotoxicity by enhancing genes involved in synaptic plasticity, attenuating neuroinflammation, and preserving metabolic function. Key PointsO_LIComplete response of medulloblastoma and reduction of neurotoxicity with hypo-fractionated FLASH regimen. C_LIO_LIClearance-prone phagocytic and proteolytic activity in the microglia of the TME. C_LIO_LINeuron/astrocyte transcriptional crosstalk in the hippocampus. C_LI Importance of the studyThis study constitutes a milestone for the future implementation of FLASH-RT in the treatment of children with brain cancer. It shows that FLASH does not protect medulloblastoma and on the contrary can be ablative when delivered in 3 fractions of 10 Gy. FLASH promotes a metabolically active, phagocytosis-prone phenotype in microglial cells consistent with immune activation and tumor surveillance, in contrast to the proliferative and immunosuppressive signaling programs induced by CONV. It also shows how FLASH may differentially shape long-term brain function in patients with brain tumors by modifying the transcriptional program of hippocampal subregions known to be critical for memory encoding, pattern separation, and consolidation. In summary, this study supports the idea that FLASH has the potential to shift treatment paradigms and change the dismal therapeutic outcome in patients with brain cancer.

Background and purposePrecise manual annotation of the left ventricular myocardial (LVM) wall is essential for cardiac substructure research, wall-specific radiation dosimetry, and segmentation model development. However, existing radiotherapy-oriented atlases and conventional CT viewing planes lack an explicit framework for reproducible, wall-level LVM delineation. To address this gap, we developed an anatomy-guided manual segmentation protocol for delineating the five LVM walls on non-contrast-enhanced CT (NECT) or contrast-enhanced CT (CECT) scans. Materials and methodsThis protocol was developed using 60 chest CT scans from two prospective cohorts at Heidelberg University Hospital, including 50 CECTs from IMRT-MC2 cohort and 10 NECTs from MAGELLAN cohort. Manual contouring was performed in 3D Slicer. Segmentation rules were established through review by a radiation oncologist and a cardiology expert, based on the American Heart Association 17-segment model, and were tested on additional CT scans before final protocol definition. ResultsThe protocol centers on three geometric steps: (1) defining the LV long axis using the endocardial apex and the center of the mitral annulus; (2) constructing an apical delimitation plane based on LV geometry; and (3) partitioning wall regions via intersections of the right ventricular and LV cavity centers in the short-axis view. This workflow enables structured segmentation of the anterior, septal, lateral, inferior, and apical LVM walls, supporting anatomically coherent 3D reconstruction. ConclusionThis study provides contouring steps and a representative atlas as a methodological basis for standardized annotation, with potential applications in dose-mapping cardiotoxicity analysis and deep-learning modeling for radiotherapy.

BackgroundATR activation following DNA damage from cancer treatments such as radiation can mitigate anticancer efficacy, making ATR inhibitors (ATRi) an attractive therapeutic. In vivo and in vitro studies have shown enhanced tumor cell radiosensitivity with the ATRi ceralasertib, elimusertib, and berzosertib, however, the potentiating effect of ATRi on ionizing radiation (IR) through immune-based mechanisms has only been studied with ceralasertib. MethodsWe aimed to determine if antitumor immune responses observed with ceralasertib in combination with IR extend to the other ATRi class members in the preclinical CT26 mouse model. We also examined the relationship between exposure and immune stimulation, efficacy and survival outcomes of each ATRi when combined with IR. ResultsCeralasertib and elimusertib, not berzosertib, synergized with IR in a dose and schedule-dependent manner to modify tumor antigen-specific CD8+ T cell populations in the draining lymph node. Transient ATRi therapy, combined with IR, enhances antitumor efficacy, promoted tumor shrinkage, and increased survival. ATRi elicited differential inflammatory gene induction and dose-dependent unique cytotoxicity profiles in vitro. ConclusionThe immune mediated antitumor effect of ATRi combined with radiation is dose and schedule dependent, and while likely a class effect, may differ between ATRi compounds.

Optimizing radiotherapy dose distributions remain a resource-intensive bottleneck. Existing AI-based dose prediction methods often have limited generalizability because they rely on small, heterogeneous datasets. We present nnDoseNetv2, an auto-configured, end-to-end framework for dose prediction across diverse disease sites (head and neck, prostate, breast, and lung), prescription levels (1.5-84 Gy), and treatment modalities (IMRT, VMAT, and 3D-CRT). By integrating machine-specific beam geometry with 3D structural information, the framework is designed to generalize across varied clinical scenarios. A single multi-site model was trained on 1,000 clinical plans. On sites seen during training, performance was comparable to specialized site-specific models. On unseen sites (liver and whole brain), the model outperformed site-specific models, with mean absolute errors of 2.46% and 6.97% of prescription, respectively. These results suggest that geometric awareness can bridge disparate anatomical domains while eliminating the need for site-specific model maintenance, providing a scalable and high-fidelity approach for personalized radiotherapy planning.

Definitive radiotherapy (RT) for prostate cancer (PC) with dose intensification and/or focal boosting has excellent oncologic outcomes, but many patients experience adverse events. Dose escalation to the whole prostate improves outcomes at the expense of increased late adverse events. Intraprostatic recurrence after definitive RT typically occurs at the site of the primary tumor, suggesting that dose to the site of the dominant lesion is an important predictor of future failure. The efficacy and safety of tumor-focused RT compared to that of standard RT for definitive treatment of localized PC has not been assessed. RadTARGET (RAdiation Dose TAiloRing Guided by Enhanced Targeting) is a phase II randomized trial that aims to demonstrate superior safety of image-guided, tumor-focused RT compared to standard RT for acute genitourinary (GU) or gastrointestinal (GI) in the setting of definitive RT for intermediate- and high-risk PC. The study intervention is image-guided, tumor-focused RT with dose intensification of cancer visible on imaging and dose de-intensification to remaining prostate. Patients will be randomized to two arms: those who receive standard RT dose and those that receive tumor-focused RT. The study population will be patients with intermediate- or high-risk PC planning to undergo definitive RT with or without systemic therapy. The primary endpoint to compare between randomized arms is acute GU or GI grade [&ge;]2 adverse events. Participant and study duration are 5 years and 8 years, respectively. RadTARGET will compare the efficacy and safety of tumor-focused RT to that of standard RT for definitive treatment of localized PC. We hypothesize that the tumor-focused approach will substantially reduce adverse events after prostate RT while retaining high efficacy. If this hypothesis is confirmed, we will conclude that a phase III randomized control trial is warranted to formally establish oncologic non-inferiority compared to the current standard of whole-gland dose escalation.

The purpose of this work is to analyze the 2-year overall survival (OS2y) of limited-stage small cell lung cancer (LS-SCLC) treated with chemoradiotherapy (CRT), aiming at characterizing the response of LS-SCLC, and in particular the /{beta} value and proliferation parameters. Through a systematic analysis of the literature, we collated a dataset containing 57 entries (3363 patients) of response of LS-SCLC treated with CRT. Radiotherapy schedules ranged from hyper- to hypofractionation. Four radiobiological models to describe the OS2y were investigated, with progressive levels of complexity including the effect of radiotherapy, chemotherapy, treatment year and toxicity. The Akaike Information Criterion (AIC) was used to compare models, and the profile likelihood methodology to compute confidence intervals. Model 4, which includes the effect of radiotherapy, chemotherapy, treatment year and dose-dependent toxicity, provided the best fits of the experimental data (lowest AIC value). While being the best model, model 4 still fails to provide a good prediction of the OS2y, in particular failing to predict the survival of the schedules achieving the lower/higher survivals. The radiobiological analysis of the dose-response of LS-SCLC to CRT does not allow to narrowly constrain the value of response parameters. We attribute this limitation to the large heterogeneity of this disease. Nonetheless, our analysis shows a large /{beta} value (>9 Gy, 95% CI), which implies a low fractionation effect in the radiotherapy of LS-SCLC. and an accelerated proliferation of tumor cells, {lambda}' > 1.6 Gy/day (95% CI), after a kick-off time of ~4-5 weeks, which supports the use of accelerated protocols to avoid the effect of tumor proliferation on the clinical outcome.

Background: Prostate-specific membrane antigen (PSMA) PET/CT is central to prostate cancer staging and theranostic workflows. To our knowledge, no direct within-patient comparison of [18F]FC303 ([18F]Florastamin) and [68Ga]Ga-PSMA-11 has been reported. We performed a preliminary paired method-comparison study under non-harmonized acquisition protocols. Patients and Methods: Twenty patients with histologically confirmed prostate cancer underwent [68Ga]Ga-PSMA-11 PET/CT (185 +/- 37 MBq, 60 +/- 10 min) followed by [18F]FC303 PET/CT (370 +/- 37 MBq, 105 +/- 15 min) on the same PET/CT system within each patient (median interval, 29.5 days). Index targets were anatomically matched to the biopsied or surgically sampled lesion or target region. The primary malignant set included 18 histologically malignant targets; two histology-negative or indeterminate targets were included only in sensitivity analysis. Fixed [68Ga]Ga-PSMA-11-first scan order and the 45-min uptake-time difference were central interpretive constraints. Results: Across five predefined reference organs, [18F]FC303 showed lower SUVmean than [68Ga]Ga-PSMA-11 (all Benjamini-Hochberg-adjusted p < 0.001; [68Ga]/[18F]FC303 geometric mean ratio [GMR], 1.29-3.89). In the primary malignant set, [18F]FC303 lesion SUVmax was lower than [68Ga]Ga-PSMA-11 (median, 11.3 vs 18.1; paired median difference, -5.50; 95% CI, -6.85 to -2.90; Wilcoxon p = 8.4 x 10-4), with strong rank correlation (Spearman {rho} = 0.90). Passing-Bablok regression yielded {beta} = 1.13 (95% CI, 1.04-1.45), and log-Bland-Altman GMR (FC303/[68Ga]) was 0.75, consistent with proportional non-interchangeability. Tumor-to-liver and tumor-to-mediastinum ratios did not differ significantly (GMR, 1.17 [95% CI, 0.94-1.45] and 0.96 [0.80-1.15], respectively); the study was not powered for equivalence. The n = 20 sensitivity analysis showed consistent directionality. Conclusions: Under non-harmonized acquisition conditions, [18F]FC303 showed lower physiologic reference-organ SUVmean and malignant target-region SUVmax than [68Ga]Ga-PSMA-11, whereas tumor-to-liver and tumor-to-mediastinum ratios were not significantly different. Absolute SUVs were not interchangeable; [68Ga]Ga-PSMA-11-derived SUV thresholds should not be directly transferred to [18F]FC303 without tracer-specific calibration.

BackgroundRadiation therapy is integral to the curative treatment of childhood brain tumors but contributes to late neurocognitive impairment in survivors. FLASH (ultra-high dose rate, >40Gy/s) reduces normal-tissue toxicity in preclinical models, and proton-FLASH is currently the only modality capable of delivering ultra-high dose rates to the deep targets, such as pediatric brain tumors. However, two questions remain unresolved before clinical translation: (1) whether the FLASH effect can be achieved on synchrotron-based proton systems, which deliver protons in discrete spills that may be insufficient to cover a clinical target within a single delivery, and (2) which dose-rate metric, among the multiple definitions currently used in the field, best predicts the biological FLASH effect. MethodsC57BL/6 mice (7-8 weeks) received 10 Gy whole-brain RT via a clinical Hitachi ProBEAT synchrotron with CBCT-guided delivery, using three transmission-beam techniques: single-spill pencil beam scanning (SS PBS), multi-spill PBS with [~]2-second inter-spot delay (MS PBS), and passive scatter (PS), compared to conventional (CONV) delivery and unirradiated controls (n=24-28/group, equal sex distribution). Dose rate was quantified using three frameworks: field dose rate (FDR), PBS dose rate (PBSDR), and dose-averaged dose rate (DADR). Recognition memory was assessed by novel object recognition (NOR) at 6 weeks post-RT, and cognitive flexibility was assessed via touchscreen visual discrimination and reversal learning at 14 weeks. Hippocampal neuroinflammation was evaluated by immunofluorescence and immunohistochemistry for Iba1, NeuN, and GFAP. ResultsFLASH conditions were met by SS PBS and PS under all three dose-rate definitions, but MS PBS qualified as FLASH only by DADR. Despite this, neuroprotection was preserved across all three FLASH techniques: discrimination index was significantly higher for SS PBS (P=0.021), MS PBS (P=0.008), and PS (P<0.001) versus CONV, with no significant difference between FLASH techniques. On touchscreen testing, FLASH-treated females demonstrated preserved cognitive flexibility (P=0.047 vs. CONV on reversal learning correct trials). Iba1+ microglia were reduced in FLASH compared to CONV mice, with morphology suggestive of preserved homeostatic state. ConclusionsSynchrotron-based proton FLASH preserves neurocognitive function across all delivery techniques, including under multi-spill delivery essential for treating clinical-scale pediatric brain tumors. Critically, this neuroprotection was observed even for deliveries that qualified as FLASH only by DADR, identifying DADR as the dose-rate metric most relevant to the biological FLASH effect with direct implications for clinical trial design and dose-rate reporting standards.