PURPOSE:The lens of the eye has been recognized as one of the most radiosensitive tissues in the human body. Radiation-induced cataractogenesis is believed to arise through a complex interplay of molecular processes, including crystallin protein oxidation and aggregation, impaired antioxidant defenses, apoptosis of lens epithelial cells, and epithelial-mesenchymal transition. Nonetheless, the precise mechanisms responsible for these changes remain to be fully elucidated. Organoid model systems are an emerging tool that provide a novel approach for investigating disease processes. In this study, we examined transcriptional changes in lentoid bodies, an organoid-like model of the ocular lens, following exposure to ionizing radiation. MATERIALS AND METHODS:Lentoid bodies were generated from human pluripotent stem cells through a three-step differentiation protocol. Mature lentoid bodies were then subjected to an x-ray dose of 0.25 or 2 Gy and RNA was isolated 12, 24, and 48 hours post exposure for whole transcriptome RNA-sequencing. Genes were considered differentially expressed if they exhibited a fold change < -2.0 or >2.0, false discovery rate-corrected p-value <0.05, and a minimum average read count of 30 transcripts per million. RESULTS:Significant changes in gene expression profiles were observed post-irradiation with both dose and time post-exposure playing critical roles in the extent and nature of gene dysregulation. Differentially expressed genes were identified within key biological pathways implicated in cataract formation, including cell survival and proliferation, differentiation, migration, and epithelial-mesenchymal transition. CONCLUSIONS:These results advance our understanding of the molecular mechanisms underlying radiation-induced cataracts and demonstrate the value of lens organoid models as a physiologically relevant platform, offering insights beyond those achievable with conventional lens cell lines.

The anhydrobiotic (living without water) yeast Saccharomyces cerevisiae has gained considerable interest for its use in a variety of fields, from investigation of the biological effects of deep space radiation exposure to its utilization as a radiation dosimeter and its applicability in the study of preservation of microbial life in martian regolith. A complete radiobiological characterization of yeast during anhydrobiosis must be undertaken to ensure the informed interpretation of these works. This study investigated the radiobiological properties of a desiccated recombinational repair-deficient rad51 knockout strain of S. cerevisiae. We focused on radiation tolerance, oxygen enhancement ratio (OER), and relative biological effectiveness (RBE). Desiccation-induced radioresistance was significantly higher compared with hydrated yeast; it required a threefold higher dose for an equivalent biological response. Desiccated yeast exhibited no OER, which indicates the absence of oxygen-dependent radiosensitization due to the lack of indirect damage pathways. RBE measurements for a 74 MeV proton beam (1.10 ± 0.01) and a neutron beam (12.2 ± 0.7) align with prior studies and demonstrate consistency between desiccated and hydrated systems when appropriately scaled. These findings support the use of the desiccated yeast model as a robust and translatable system for addressing fundamental questions in astrobiology and radiobiology.

Radiation resistance presents a significant challenge in the treatment of triple-negative breast cancer (TNBC). To investigate the molecular adaptations associated with radiation therapy resistance, MDA-MB-231 cells were subjected to a repeated radiation (RR) regimen totaling 57 Gy over 11 weeks, followed by clonal selection. The resulting radiation-adapted cells (MDA-MB-231RR) were analyzed using whole-transcriptome RNA sequencing, revealing substantial dysregulation of pathways related to cell adhesion, mitochondrial function, and epithelial-mesenchymal transition (EMT). These transcriptional changes were corroborated by functional assays. MDA-MB-231RR cells exhibited reduced expression of adhesion receptors (ITGB1, ITGA2, ITGA6) and extracellular matrix proteins (fibronectin, collagen, laminins), accompanied by significantly impaired cell adhesion to fibronectin, collagen, and laminin substrates. Mitochondrial dysfunction was supported by downregulation of oxidative phosphorylation genes (MTCO1, MTND1) and confirmed by JC-1 dye assays demonstrating a marked reduction in mitochondrial membrane potential. EMT-associated changes included increased mesenchymal markers and loss of epithelial markers (CTNNB1, SNAI2, CK19), consistent with enhanced migratory potential. Taken together, this study delineates key molecular features of radiation adaptation in TNBC, providing a foundation for the development of targeted therapies to overcome treatment resistance.

Objective. Due to higher dose conformality to the target, proton radiotherapy for cancer has received rapidly-growing interest. However, uncertainties in thein vivoproton range and methods to reduce them remain active areas of research. Based on 20 patients with head-and-neck cancer, this study aims to quantify the benefits of proton range uncertainty reductions in terms of the resulting improvements in quality-adjusted life expectancy (QALE).Approach. For each patient, two different proton therapy treatment plans were created, which assumed a current clinical range uncertainty of approximately 3.5% (IMPT3.5%) and a potentially achievable range uncertainty of 1.0% (IMPT1%). A Markov model considering the probability of tumor control and the development of xerostomia, larynx edema, secondary cancer, and/or metastases as well as death from primary cancer, secondary cancer, metastases, or unrelated causes was constructed, and for every patient and treatment plan, 10 000 simulations of the patient's entire lifetime from the time of treatment until death were performed.Main results.A 3.5%-1% range uncertainty reduction increased QALE by up to 0.4 quality-adjusted life years (QALYs) in the nominal and up to 0.6 QALY in the worst-case scenario, equivalent to 4.8 months and 7.2 months of life in perfect health. This was largely the result of a reduction in healthy tissue toxicity rates, which were reduced by up to 8.5 percentage points (pp) and 10.0 pp in the nominal and worst-case scenario, respectively.Significance. The benefits of a 3.5%-1% range uncertainty reduction in 20 patients with head-and-neck cancer were quantified in terms of the associated improvement in QALE. The highest QALE improvements were observed in patients in the top quartile of youngest patients at the time of treatment, due to the longer potential lifespan over which prevented healthy tissue toxicities would have impacted the patients' quality of life.

Objectives Exposure of the developing fetus to high doses of ionizing radiation during prenatal development can result in growth restriction of the fetus, or a reduction in offspring growth. The developmental stage of the offspring at the time of irradiation is of interest, in order to characterize any potential periods of sensitivity for radiation-induced growth restriction effects. The goal of the present study was the development of a mouse model of radiation-induced growth restriction, following X-ray irradiation during late gestation. Methods Pregnant BALB/cAnNCrl mice were irradiated with different irradiation conditions from gestational day (GD) 14-17. Treatments included an acute dose of 1.82 Gy X-ray irradiation on GD 14, 15 or 16. The effects of dose fractionation were also studied with one group receiving 0.455 Gy x 4 daily fractions from GD 14-17 (cumulative dose of 1.82 Gy). Another group also received a pre-treatment with 61 mGy X-ray irradiation on GD 14, 24 h prior to the 1.82 Gy on GD 15, to test for the possibility of a radiation-induced adaptive response. Results Evidence for growth restriction was observed in all irradiation groups, with the greatest degree of growth restriction observed in the 1.82 Gy on GD 14 group. Evidence for growth restriction was based on a reduced gestational weight gain by pregnant dams and significant decrease in fetal weight and length measurements. Evidence for an adaptive response was not observed in the present study, as the combination group had similar outcomes to the group that only received the 1.82 Gy challenge irradiation dose. Conclusion The establishment of a mouse model of radiation-induced growth restriction during late gestation will facilitate the ability for future work into determining the precise cellular and physiological effects on offspring, and the development of future countermeasures to protect against such adverse effects.

High doses of ionizing radiation during prenatal development can cause growth restriction, or a decrease in growth of the developing offspring. This outcome of intrauterine growth restriction (IUGR) can predispose the offspring to lifelong health outcomes, which is referred to as developmental programming. The role of the placenta in radiation-induced IUGR was investigated using a mouse model. Pregnant BALB/cAnNCrl mice were externally irradiated with 1.82 Gy x-ray irradiation on gestational day 14.5. Fetoplacental units were collected on gestational day 18.5, and growth restriction was observed in irradiated offspring. Whole placenta samples from growth restricted and sham-irradiated groups were analyzed via RNA-sequencing analysis. Differential gene expression (DEG) analysis revealed a total of 166 DEGs in the irradiated samples. Validation of these DEG findings were completed using RT-qPCR analysis. Gene ontology (GO) analysis of the DEGs supported the involvement of autoimmune response and dysregulation in retinol (vitamin A) metabolism in the placenta. Upstream prediction analysis identified a number of potential regulators responsible for the DEG profiles including Nppb, Myod1 and genes of the classic complement system (Complement C1q chains C1qa, C1qb, C1qc). Overall, these findings present an overview of the dysregulation in the mouse placenta following an acute, high-dose radiation exposure.

Ionizing radiation exposure during perinatal development can produce various biological effects on the developing offspring. These effects are dependent on a number of factors, including total dose, dose rate and the developmental processes occurring at the time of irradiation. The present study conducted an analysis of historical radiobiological archived data involving 60Co-gamma irradiation of beagle dogs at specific periods of prenatal or postnatal development. The original studies were performed at two sites where animals were exposed to a single, acute dose of 0.2 or 1.0 Gy at six different stages of perinatal development or with protracted exposures ranging from 0.004 to 0.35 Gy per day, over multiple days of gestation. A number of outcomes were investigated after perinatal irradiation including changes in sex ratio, survival probability, disease incidence and growth of animals, based on collected size and weight measurements of animals and different tissues. Protracted irradiations with doses up to 0.35 Gy per day did not significantly affect survival in animals when irradiated prenatally, although significant increases in the incidence of neoplasms and diseases related to the cardiovascular and urogenital system were observed at the time of death. Dogs irradiated at a dose rate of 0.10 Gy per day, with the irradiations continuing after birth and resulting in the accumulation of large total doses, were observed to have chronic radiation syndrome symptoms based on pathologies related to the hematopoietic system. Acute irradiation with 0.2 and 1.0 Gy resulted in changes of different body or tissue sizes measured in animals terminally, with changes detected after irradiation at all tested prenatal and postnatal time points, with the exception of irradiation at 365 days after birth. The present analysis provides new information regarding the biological effects of ionizing radiation during perinatal development in offspring in the unique mammalian study model of the beagle dog.

PurposeFOS-like antigen 1 (FRA1), encoded by FOSL1, is an inducible subunit of the AP-1 transcription factor complex and regulates gene expression in response to proliferative and environmental cues. Although FRA1 has been linked to cancer progression, its role in early transformation and radiation responses remains unclear.MethodsCRISPR-engineered human CGL1 cells—a hybrid of HeLa and normal fibroblasts—were used to evaluate the impact of FRA1 overexpression and knockout on neoplastic transformation. Transformation frequency, clonogenic survival, DNA damage recognition and repair, and cell cycle distribution were assessed following irradiation. Transcriptomic profiling was performed under baseline and serum-stimulated conditions.ResultsFRA1 loss markedly increased both spontaneous and radiation-induced transformation frequency, while overexpression suppressed transformation under both conditions. FRA1-deficient cells were sensitized to radiation-induced cell killing, despite intact DNA damage recognition and repair. In contrast, FRA1 overexpression promoted G2/M accumulation post-irradiation, suggesting enhanced checkpoint activation. Transcriptomic profiling revealed that FRA1 remodels AP-1 complex composition and functions as a transcriptional repressor of mitogen- and stress-responsive genes. FRA1-mediated repression was observed across gene networks involved in extracellular matrix remodeling, hypoxia signaling, inflammation, and proliferation, under both baseline and serum-stimulated conditions.ConclusionThese findings establish FRA1 as a key modulator of neoplastic transformation and radiation response, acting primarily through transcriptional repression of pro-tumorigenic signaling pathways.

Breast cancer remains one of the most prevalent malignancies worldwide, and radiation therapy is a central component of its management. However, intrinsic or acquired resistance to radiation significantly compromises therapeutic efficacy. This systematic review aimed to identify and evaluate molecular mechanisms and interventions that influence radiation sensitivity in breast cancer models. A comprehensive PubMed search was conducted using the terms “breast cancer” and “radiation resistance” for studies published between 2002 and 2024. Seventy-nine eligible studies were included. The most frequently investigated mechanisms included the dysregulation of the PI3K/AKT/mTOR and MAPK signaling pathways, enhanced DNA damage repair via non-homologous end joining (NHEJ), and the overexpression of cancer stem cell markers such as CD44+/CD24−/low and ALDH1. Several studies highlighted the role of non-coding RNAs, particularly the lncRNA DUXAP8 and microRNAs such as miR-21, miR-144, miR-33a, and miR-634, in modulating radiation response. Components of the tumor microenvironment, including cancer-associated fibroblasts and immune regulators, also contributed to radiation resistance. By synthesizing current evidence, this review provides a consolidated resource to guide future mechanistic studies and therapeutic development. This review highlights promising molecular targets and emerging strategies to enhance radiosensitivity and offers a foundation for translational research aimed at improving outcomes in radiation-refractory breast cancer.

Objective MicroRNAs (miRNAs) are small, non-coding RNA molecules that regulate gene expression and remain stable in biological fluids, even under harsh conditions. Their stability and responsiveness to environmental stressors make them strong candidates for radiation biodosimetry. This study aimed to (1) establish a robust in vivo pipeline for miRNAome profiling and (2) identify plasma-based miRNA biomarkers of ionizing radiation at low and high doses. Methods BALB/c mice were exposed to sham, 100 mGy, or 2 Gy of X-rays. Plasma was collected 6 h post-irradiation. Total RNA was extracted, and next-generation sequencing was used to profile the plasma miRNAome. Differentially expressed miRNAs were identified relative to sham controls, and selected candidates were validated using RT-qPCR. Results A total of 630 unique miRNAs were detected. High-dose exposure (2 Gy) significantly upregulated 14 and downregulated 5 miRNAs. Seven miRNAs were significantly induced at 100 mGy, including miR-126a-5p and miR-133a-3p, which were exclusive to low-dose exposure. Five miRNAs were shared between both doses, indicating dose-independent responses. RT-qPCR confirmed expression trends. Conclusion This study identified distinct and shared circulating miRNA signatures for low- and high-dose radiation exposure. These findings support the potential of miRNAs as minimally invasive, dose-stratified biomarkers for radiation biodosimetry.

Natural background ionizing radiation is present on the earth's surface; however, the biological role of this chronic low-dose-rate exposure remains unknown. The Researching the Effects of the Presence and Absence of Ionizing Radiation (REPAIR) project is examining the impacts of sub-natural background radiation exposure through experiments conducted 2 km underground in SNOLAB. The rock overburden combined with experiment-specific shielding provides a background radiation dose rate 30 times lower than on the surface. We hypothesize that natural background radiation is essential for life and maintains genomic stability and that prolonged exposure to sub-background environments will be detrimental to biological systems. To evaluate this, human hybrid CGL1 cells were continuously cultured in SNOLAB and our surface control laboratory for 16 weeks. Cells were assayed every 4 weeks for growth rate, alkaline phosphatase (ALP) activity (a marker of cellular transformation in the CGL1 system), and the expression of genes related to DNA damage and cell cycle regulation. A subset of cells was also exposed to a challenge radiation dose (0.1 to 8 Gy of X rays) and assayed for clonogenic survival and DNA double-strand break induction to examine if prolonged sub-background exposure alters the cellular response to high-dose irradiation. At each 4-week time point, sub-background radiation exposure did not significantly alter cell growth rates, survival, DNA damage, or gene expression. However, cells cultured in SNOLAB showed significantly higher ALP activity, a marker of carcinogenesis in these cells, which increased with longer exposure to the sub-background environment, indicative of neoplastic progression. Overall, these data suggest that sub-background radiation exposure does not impact growth, survival, or DNA damage in CGL1 cells but may lead to increased rates of neoplastic transformation, highlighting a potentially important role for natural background radiation in maintaining normal cellular function and genomic stability.

We derived the first comprehensive organ dose library for Canadian pediatric and adult patients who underwent computed tomography (CT) scans between 1992 and 2019 to support epidemiological analysis of radiation risk. We calculated organ absorbed doses for Canadian CT patients in two steps. First, we modeled Computed Tomography Dose Index (CTDI) values by patient age, scan body part, and scan year for the scan period between 1992 and 2019 using national survey data conducted in Canada and partially the United Kingdom survey data as surrogates. Second, we converted CTDI values to organ absorbed doses using a library of organ dose conversion coefficients built in an organ dose calculation program, the National Cancer Institute dosimetry system for CT. In result, we created a library of doses delivered to 33 organs and tissues by different patient ages and genders, scan body parts and scan years. In the scan period before 2000, the organs receiving the greatest dose in the head, chest and abdomen-pelvis scans were the active marrow (3.7-15.2 mGy), lungs (54.7-62.8 mGy) and colon (54.9-68.5 mGy), respectively. We observed organ doses reduced by 24% (pediatric head and torso scans, and adult head scans) and 55% (adult torso scans) after 2000. The organ dose library will be used to analyse the risk of radiation exposure from CT scans in the Canadian CT patient cohort.

Ionizing radiation is one of the known risk factors for cataract development, however, there is still debate regarding the level of risk after low dose exposures. One of the largest sources of radiation exposure to the lens of the eye is diagnostic CT scans. The aim of this study was to examine whether ionizing radiation associated with head CT scans increases cataract risk in residents of Ontario, Canada. Data were collected from January 1, 1994 to December 31, 2015 (22 years) from anonymized Ontario Health Insurance Plan (OHIP) medical records for over 16 million subjects. A lens dose was estimated for each CT scan using the National Cancer Institute dosimetry system for CT (NCICT) program combined with Canada-specific CTDIvol data. Multivariate Cox proportional hazards analysis was performed with cataract extraction surgery as the primary outcome and lens dose as the main variable of interest, with inclusion of various medical and demographic covariates. Lag periods of 3, 5 and 7 years were incorporated. When lens dose was treated as a continuous variable, hazard ratios (per 100 mGy) ranged from 0.82 (0.80–0.84) to 1.10 (1.09–1.11) depending on the lag period. As a secondary analysis, when individuals were binned based on their total cumulative dose, no significant dose response pattern was observed in the low dose region. Overall, within the bounds of this study, the data do not support an increased risk of vision impairing cataracts after diagnostic head CT scan radiation exposure.

Objective. Proton therapy reduces the integral dose to the patient compared to conventional photon treatments. However, in vivo proton range uncertainties remain a considerable hurdle. Range uncertainty reduction benefits depend on clinical practices. During intensity-modulated proton therapy (IMPT), the target is irradiated from only a few directions, but proton arc therapy (PAT), for which the target is irradiated from dozens of angles, may see clinical implementation by the time considerable range uncertainty reductions are achieved. It is therefore crucial to determine the impact of PAT on range uncertainty reduction benefits. Approach. For twenty head-and-neck cancer patients, four different treatment plans were created: an IMPT and a PAT treatment plan assuming current clinical range uncertainties of 3.5% (IMPT3.5% and PAT(3.5%)), and an IMPT and a PAT treatment plan assuming that range uncertainties can be reduced to 1% (IMPT1% and PAT(1%)). Plans were evaluated with respect to target coverage and organ-at-risk doses as well as normal tissue complication probabilities (NTCPs) for parotid glands (endpoint: parotid gland flow <25%) and larynx (endpoint: larynx edema). Main results. Implementation of PAT (IMPT3.5%-PAT(3.5%)) reduced mean NTCPs in the nominal and worst-case scenario by 3.2 percentage points (pp) and 4.2 pp, respectively. Reducing range uncertainties from 3.5% to 1% during use of IMPT (IMPT3.5%-IMPT1%) reduced evaluated NTCPs by 0.9 pp and 2.0 pp. Benefits of range uncertainty reductions subsequently to PAT implementation (PAT(3.5%)-PAT(1%)) were 0.2 pp and 1.0 pp, with considerably higher benefits in bilateral compared to unilateral cases. Significance. The mean clinical benefit of implementing PAT was more than twice as high as the benefit of a 3.5%-1% range uncertainty reduction. Range uncertainty reductions are expected to remain beneficial even after PAT implementation, especially in cases with target positions allowing for full leveraging of the higher number of gantry angles during PAT.

ABSTRACT:Experiments that examine the impacts of subnatural background radiation exposure provide a unique approach to studying the biological effects of low-dose radiation. These experiments often need to be conducted in deep underground laboratories in order to filter surface-level cosmic radiation. This presents some logistical challenges in experimental design and necessitates a model organism with minimal maintenance. As such, desiccated yeast ( Saccharomyces cerevisiae ) is an ideal model system for these investigations. This study aimed to determine the impact of prolonged sub-background radiation exposure in anhydrobiotic (desiccated) yeast at SNOLAB in Sudbury, Ontario, Canada. Two yeast strains were used: a normal wild type and an isogenic recombinational repair-deficient rad51 knockout strain ( rad51 Δ). Desiccated yeast samples were stored in the normal background surface control laboratory (68.0 nGy h -1 ) and in the sub-background environment within SNOLAB (10.1 nGy h -1 ) for up to 48 wk. Post-rehydration survival, growth rate, and metabolic activity were assessed at multiple time points. Survival in the sub-background environment was significantly reduced by a factor of 1.39 and 2.67 in the wild type and rad51 ∆ strains, respectively. Post-rehydration metabolic activity measured via alamarBlue reduction remained unchanged in the wild type strain but was 26% lower in the sub-background rad51 ∆ strain. These results demonstrate that removing natural background radiation negatively impacts the survival and metabolism of desiccated yeast, highlighting the potential importance of natural radiation exposure in maintaining homeostasis of living organisms.

Background Oral mucositis is a painful and debilitating condition that occurs in the majority of head and neck cancer patients receiving radiation and/or chemotherapy. While some patient and treatment related factors are known to contribute to the incidence and severity of disease, reliable biomarkers remain elusive. In the following study, we investigated the association of salivary DNA methylation derived biological aging, cellular frequency and protein concentration measures with the severity of oral mucositis and overall survival in a cohort of head and neck cancer (HNC) patients (n = 103). Methods DNA methylation profiling was performed on saliva samples obtained prior to treatment. Biological aging measures included Horvath2, PhenoAge, FitAge and GrimAge, and cellular frequency included epithelial and specific immune cell populations. Results Severe mucositis (i.e. grade 3 or 4) occurred in nearly half of patients. For malignant HNC patients (n = 84), every 1-SD increase in GrimAge was associated with 2.62-times risk of severe mucositis (95 % CI: 1.38, 5.57), while a 1-SD increase in monocyte frequency was associated with a decreased risk (OR [95 %CI]: 0.40 [0.18, 0.80]). Over a median follow-up of 53 months, 39 of 103 participants died. Six protein scores (TNFSF14, GCSF, MATN3, GDF8, nCDase, TNF-β) were associated with survival at q < 0.15. Conclusion We provide evidence that the risk-related biological aging measure GrimAge may be a useful predictor of mucositis severity in HNC patients. Salivary monocyte frequency may be protective against mucositis, and this measure could be used as a predictive biomarker while also providing clues into the pathobiology of the disease.

Radiation therapy for abdominopelvic malignancies often results in damage to the gastrointestinal tract (GIT) and permanent changes in bowel function. An overlooked component of the pathophysiology of radiation-induced bowel injury is the role of the gut microbiome. The goal of this research was to identify the impacts of acute radiation exposure on the GIT and gut microbiome. C57BL/6 mice exposed to whole-body X-rays (0.1–3 Gy) were assessed for histological and microbiome changes 48 h post-radiation exposure. Within the ileum, a dose of 3 Gy significantly decreased crypt depth as well as the number of goblet cells, but increased overall goblet cell size. Overall, radiation altered the microbial distribution within each of the main phyla in a dose- and tissue-dependent manner. Within the Firmicutes phylum, high dose irradiation resulted in significant alterations in bacteria from the class Bacilli within the small bowels, and from the class Clostridia in the large bowels. The 3 Gy radiation also significantly increased the abundance of bacterial families from the Bacteroidetes phylum in the colon and feces. Overall, we identified various alterations in microbiome composition following acute radiation exposure, which could potentially lead to novel biomarkers for tracking patient toxicities or could be used as targets for mitigation strategies against radiation damage.

Purpose/Objective Proton therapy for cancer reduces the integral radiation dose to the patient compared to conventional photon treatments.1 The number of proton therapy centers globally has been growing rapidly as a result, but uncertainties in the in vivo proton range remain a considerable hurdle.2,3 A variety of different approaches to reduce proton range uncertainties are therefore currently being pursued.4,5,6,7,8,9,10 The associated benefits have been quantified previously but depend on clinical practices, including the number of gantry angles from which the tumor is irradiated.11,12,13,14 For conventional proton therapy techniques like intensity-modulated proton therapy (IMPT), the target is irradiated from only a few directions, but proton arc therapy (PAT), for which the target is irradiated from hundreds of angles, may see clinical implementation by the time considerable range uncertainty reductions are achieved.15,16,17,18,19 It is therefore crucial to determine the impact of PAT implementation on the importance of range uncertainty reductions. Material/Methods Five head-and-neck cancer patients were randomly selected from The Radiotherapy Optimization Test Set (TROTS).20 For each patient, four different radiotherapy treatment plans were created in Version 6.0 of RayStation (RaySearch Laboratories, Stockholm, Sweden): an IMPT and a PAT treatment plan assuming current clinical range uncertainties of 3.5% (IMPT3.5% and PAT3.5%), and an IMPT and a PAT treatment plan assuming that range uncertainties can be reduced to 1% (IMPT1% and PAT1%). Treatment plans were evaluated with respect to target coverage and organ-at-risk (OAR) doses as well as normal tissue complication probabilities (NTCPs) resulting from organ irradiation during radiotherapy delivery. NTCPs were determined for both parotid glands (endpoint: parotid gland flow < 25% compared to pre-treatment after one year (grade 4 xerostomia)) and the larynx (endpoint: grade ≥ 2 larynx edema).21,22,23 In accordance with clinical practice, radiotherapy treatment planning assumed a patient setup uncertainty of 3 mm, and dose calculations applied a constant relative biological effectiveness (RBE) value of 1.1 to account for differences between proton and photon irradiation.12 Results For all four types of treatment plans and all delineated organs, OAR doses are shown in Table 1. Values are given in the nominal delivery scenario (in which neither patient setup nor proton range errors occur) as well as in the worst-case scenario (in which errors in patient setup and/or the proton range do occur during treatment delivery) and constitute average values over all five patients. On average, implementation of PAT (IMPT3.5%-PAT3.5%) reduced NTCPs in the nominal and worst-case scenario by 2.51 percentage points (pp) and 3.96 pp, respectively. In comparison, reducing range uncertainties from 3.5% to 1% during continued use of IMPT (IMPT3.5%-IMPT1%) reduced evaluated NTCPs by 0.64 pp and 1.27 pp, respectively. Average benefits of range uncertainty reductions subsequently to PAT implementation (PAT3.5%- PAT1%) were 0.81 pp in the nominal and 1.78 pp in the worst-case scenario.Table 1 Organ-at-risk doses for all four types of treatment plans averaged over all five patients. Nom and WC refer to the nominal and the worst-case delivery scenario, respectively. All values are in units of Gy(RBE) and concern the mean dose within the organ in question, with the exception of the brainstem and the spinal cord, for which the maximum value within the organ is given. SMG refers to the submandibular glands while other abbreviations indicate swallowing muscles. Conclusion The average clinical benefit of implementing PAT was approximately three times higher than the benefit of a 3.5% to 1% range uncertainty reduction during continued use of IMPT. Reducing range uncertainties provided a similar clinical benefit for PAT and IMPT. Range uncertainty reductions are therefore expected to remain beneficial even when achieved subsequently to or in tandem with PAT implementation.

PURPOSE:Exposure to ionizing radiation is one of the known risk factors for the development of lens opacities. It is believed that radiation interactions with lens epithelial cells (LEC) are the underlying cause of cataract development, however, the exact mechanisms have yet to be identified. The aim of this study was to investigate how different radiation dose and fractionation impact normal LEC function. MATERIALS AND METHODS:A human derived LEC cell line (HLE-B3) was exposed to a single acute x-ray dose (0.25 Gy) and 6 fractionated doses (total dose of 0.05, 0.1, 0.25, 0.5, 1, and 2 Gy divided over 5 equal fractions). LEC were examined for proliferation using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and migration using a Boyden chamber assay at various time points (0.25, 0.5, 1, 2, 4, 7, 9, 11, and 14 d) post-irradiation. Transcriptomic analysis through RNA sequencing was also performed to identify differentially expressed genes and regulatory networks in cells following 4 different acute exposures and 1 fractionated exposure. RESULTS:Exposure to an acute dose of 0.25 Gy significantly increased proliferation and migration rates, peaking at 7 d post irradiation (20% and 240% greater than controls, respectively), before returning to baseline levels by day 14. Fractionated exposures had minimal effects up to a dose of 0.5 Gy, but significantly reduced proliferation and migration after 1 and 2 Gy by up to 50%. The largest transcriptional response occurred 12 h after an acute 0.25 Gy dose, with 362 genes up-regulated and 288 genes down-regulated. A unique panel of differentially expressed genes was observed between moderate versus high dose exposures, suggesting a dose-dependent transcriptional response in LEC that is more pronounced at lower doses. Gene ontology and upstream regulator analysis identified multiple biological processes and molecular functions implicated in the radiation response, in particular differentiation, motility, receptor/ligand binding, cell signaling and epithelial-mesenchymal cell transition. CONCLUSIONS:Overall, this research provides novel insights into the dose and fractionation effects on functional changes and transcriptional regulatory networks in LEC, furthering our understanding of the mechanisms behind radiation induced cataracts.