Single-dose Irradiation Research Articles

Deleting Trim33 in myeloid cells improves the efficiency of radiotherapy through an interferon beta dependent anti-tumor immune response.

Radiotherapy (RT) triggers an immune response that contributes to anti-tumor effects. Induction of interferon beta (IFN-β) is a key event in this immunogenicity of RT. We have previously shown that TRIM33, a chromatin reader, restrains IFN-β expression in Toll-like receptor-activated myeloid cells. Here, we explored whether deleting Trim33 in myeloid cells might improve the radio-induced immune response, and subsequent efficiency of RT. We first established that Trim33-/- bone marrow-derived macrophages showed increased expression of IFN-β in response to direct irradiation, or to treatment with irradiated cancer cells, further supporting our hypothesis. We then tested the efficiency of a single dose RT in three subcutaneous and one orthotopic tumor models. In all situations, myeloid deletion of Trim33 led to a significantly improved response after RT, leading to a complete and durable response in most of the treated mice bearing orthotopic oral tumors. This effect required the IFN-I pathway, and the presence of CD8+ T lymphocytes, but not NK cells. In addition, cured mice were capable of rejecting a secondary tumor challenge, demonstrating an in situ vaccination effect. We conclude that deleting Trim33 in myeloid cells improves RT efficiency, through a mechanism involving the IFN-I pathway and the immune response. Our work suggests that myeloid Trim33 is a host factor affecting the tumor response to RT, thus representing a new potential therapeutic target for modifying RT responses.

Magnetic resonance imaging-guided single-fraction preoperative radiotherapy for early-stage breast cancer (the RICE trial): feasibility study

BackgroundOver the past decade, the adoption of screening programs, digital mammography, and magnetic resonance imaging (MRI) has increased early-stage breast cancer diagnosis rates. Mortality rates have decreased due to early detection and improved treatments, including personalized therapies. Accelerated partial-breast irradiation (APBI) is emerging as a convenient and effective treatment for some patients, with studies exploring its preoperative use. Preoperative APBI, especially with MRI guidance, offers improved tumor targeting and potentially reduced side effects. Magnetic Resonance Imaging-Guided Single-Fraction Pre-Operative Radiotherapy for Early-Stage Breast Cancer (RICE trial) aims to assess the feasibility and efficacy of MRI-guided single-dose radiotherapy (RT) for early-stage breast cancer.MethodsThe RICE study is a prospective, single-arm study evaluating single-fraction preoperative, APBI treatment for patients with early-stage breast cancer using a magnetic resonance imaging linear accelerator (MRI linac). Eligible patients enrolled in this study will have a core biopsy to confirm estrogen receptor-positive and HER2-negative sub-type. RT planning will use a planning computed tomography (CT) co-registered with a MRI with the patient in either the supine or prone position. For the diagnostic workup, [18F] fluorodeoxyglucose positron emission tomography/CT ([18F] FDG PET/CT) and [18F] fluoroestradiol positron emission tomography/CT ([18F] FES PET/CT) will be performed prior to treatment. Thirty patients will receive a single ablative RT dose of 21 Gray to the tumor. Pre-treatment and post-treatment MRI scans will be acquired at baseline and 5 weeks post-RT respectively. Breast-conserving surgery will be scheduled for 6 weeks after APBI treatment using the MRI linac.The primary study endpoint is the successful administration of a single fraction of preoperative breast RT under the guidance of an MRI linac. Secondary endpoints include evaluating the utility of MRI, [18F] FDG PET/CT, and [18F] FES PET/CT as a non-invasive method for assessing treatment response in patients undergoing single-fraction preoperative APBI.ConclusionThe RICE trial represents a significant step in breast cancer treatment, offering insights that could lead to treatment protocols with minimized RT appointments and enhanced patient outcomes.Trial registrationThis trial is registered with the Australian New Zealand Clinical Trials Registry (ANZCTR). Registered 31st of May 2021. Registration number: ACTRN12621000659808.

Elevated α/β ratio after hypofractionated radiotherapy correlated with DNA damage repairment in an experimental model of prostate cancer.

Our previous study demonstrated that the linear quadratic model appeared to be not well-suited for high dose per fraction due to an observed increase in α/β ratio as the dose per fraction increased. To further validate this conclusion, we draw the cell survival curve to calculate the α/β ratio by the clone formation experiment and then convert the fractionated radiation dose into an equivalent single hypofractionated radiation dose comparing with that on the survival curve. Western Blot and laser confocal immunofluorescence were used to detect the expression of γ-H2AX and RAD51 after different fractionated modes of radiation. We constructed a murine xenograft model, and changes in transplanted tumor volume were used to evaluate the biological effects after different fractionated radiation. The results demonstrated that when fractionated radiation dose was converted into equivalent single hypofractionated radiation dose, the effectiveness of hypofractionated radiation was overestimated. If a larger α/β ratio was used, the discrepancy tended to become smaller. γ-H2AX was higher in 24h after a single high dose radiation than the continuous expression of the DNA repair marker RAD51. This implies more irreparable damage in a single high dose radiation compared with fractionated radiation. In the murine xenograft model, the effectiveness of hypofractionated radiation was also overestimated, and additional fractions of irradiation may be required. The conclusion is that after single hypofractionated radiation, the irreparable damage in cells increased (α value increased) and some repairable sublethal damage (β value) was converted into irreparable damage (α value). When α value increased and β value decreased, the ratio increased.

Metabolomic changes in preterminal serum samples of rhesus macaques exposed to two different lethal doses of total-body gamma-radiation

Exposure to ionizing radiation induces cellular and molecular damage leading to a cascade of events resulting in tissue and organ injury. Our study strives to characterize and validate metabolomic changes in preterminal stage (immediately prior to death) samples collected from rhesus macaques lethally irradiated with one of two different doses of radiation. Peripheral blood samples were collected pre-exposure, post-exposure, and at the preterminal stage of nonhuman primates (NHPs that did not survive exposure with 7.2 Gy or 7.6 Gy total-body radiation (LD60-80/60)). We analyzed global metabolomic alterations using ultra-performance liquid chromatography (UPLC) quadrupole time-of-flight mass spectrometry (QTOF-MS) in serum samples collected at various timepoints in relation to radiation exposure. The goal of this study was to validate the metabolic shifts present in samples collected just prior to death, which were reported earlier in a preliminary study with a limited number of samples and a single dose of radiation. Here, we demonstrate that radiation exposure induced significant time-dependent metabolic alterations compared with pre-exposure samples. We observed significant metabolite dysregulation in animals exposed to 7.6 Gy compared to 7.2 Gy. Greater metabolic disruption was observed in the preterminal groups than all of the other post-irradiation timepoints in both cohorts. Metabolomic shifts in these preterminal groups also revealed consistent disturbances in sphingolipid metabolism, steroid hormone biosynthesis, and glycerophospholipid metabolism pathways. Overall, the sphingolipid metabolism pathway appears to be representative of the preterminal phenotype, confirming the results of our preliminary study. These results offer important and novel insights for identification and validation of biomarkers for lethality, and such observations would be valuable for triage during a radiological/nuclear mass casualty scenario.

Evidence of Alveolar Macrophage Metabolic Shift Following Stereotactic Body Radiation Therapy -Induced Lung Fibrosis in Mice

Radiation-induced pneumopathy is the main dose-limiting factor in cases of chest radiation therapy. Macrophage infiltration is frequently observed in irradiated lung tissues and may participate in lung damage development. Radiation-induced lung fibrosis can be reproduced in rodent models using whole thorax irradiation but suffers from limits concerning the role played by unexposed lung volumes in damage development. Here, we used an accurate stereotactic body radiation therapy preclinical model irradiating 4% of the mouse lung. Tissue damage development and macrophage populations were followed by histology, flow cytometry, and single-cell RNA sequencing. Wild-type and CCR2 KO mice, in which monocyte recruitment is abrogated, were exposed to single doses of radiation, inducing progressive (60 Gy) or rapid (80 Gy) lung fibrosis. Numerous clusters of macrophages were observed around the injured area, during progressive as well as rapid fibrosis. The results indicate that probably CCR2-independent recruitment and/or in situ proliferation may be responsible for macrophage invasion. Alveolar macrophages experience a metabolic shift from fatty acid metabolism to cholesterol biosynthesis, directing them through a possible profibrotic phenotype. Depicted data revealed that the origin and phenotype of macrophages present in the injured area may differ from what has been previously described in preclinical models exposing large lung volumes, representing a potentially interesting trail in the deciphering of radiation-induced lung damage processes. Our study brings new possible clues to the understanding of macrophage implications in radiation-induced lung damage, representing an interesting area for exploration in future studies.

High doses of radiation cause cochlear immunological stress and sensorineural hearing loss

Radiotherapy is a crucial treatment for head and neck malignancies, but it can sometimes cause sensorineural hearing loss (SNHL). Changes in the immune microenvironment and sensory neuroepithelium of the inner ear after radiation exposure remain poorly understood. This study investigated cochlear morphology and macrophages in the inner ear after high-dose irradiation. The heads of heterozygous 8-week-old Cx3cr1GFP/+ male mice were irradiated with 30Gy of X-rays and biological samples were collected on days 1, 7, and 10 after irradiation. Auditory brainstem responses were used to assess auditory function in the mice. Changes in basilar membrane hair cells, spiral ganglion neurons (SGN), and inner ear macrophages were observed using hematoxylin-eosin (HE) staining and immunofluorescence staining. The expression of inflammatory mediators in the inner ear was detected by quantitative real-time reverse transcription-polymerase chain reaction (RT-qPCR) in cochlear tissue. The results showed no significant hair cell loss after a single high dose of radiation. However, the mice developed pantonal hearing loss on day 10 when HE staining revealed SGN atrophy and immunofluorescence showed decreased neurofilament expression. The number of macrophages in the inner ear reduced over time. RT-qPCR showed that cochlear inflammatory factors and chemokines were briefly upregulated on day 1st after irradiation and then decreased over time. In conclusion, high-dose irradiation causes acute SNHL that is not associated with hair cell loss and may be related to SGN changes. Radiation-induced SNHL is associated with a reduction in cochlear macrophages and changes in the immune microenvironment, but the relationship between the two remains to be investigated.

962: Preoperative MR-guided single-dose partial breast irradiation: the ABLATIVE-2 trial (NCT05350722)

962: Preoperative MR-guided single-dose partial breast irradiation: the ABLATIVE-2 trial (NCT05350722)

Immune effects of α and β radionuclides in metastatic prostate cancer.

External beam radiotherapy is used for radical treatment of organ-confined prostate cancer and to treat lesions in metastatic disease whereas molecular radiotherapy with labelled prostate-specific membrane antigen ligands and radium-223 (223Ra) is indicated for metastatic prostate cancer and has demonstrated substantial improvements in symptom control and overall survival compared with standard-of-care treatment. Prostate cancer is considered an immunologically cold tumour, so limited studies investigating the treatment-induced effects on the immune response have been completed. However, emerging data support the idea that radiotherapy induces an immune response in prostate cancer, but whether the response is an antitumour or pro-tumour response is dependent on the radiotherapy regime and is also cell-line dependent. In vitro data demonstrate that single-dose radiotherapy regimes induce a greater immune-suppressive profile than fractionated regimes; less is known about the immune response induced by molecular radiotherapy agents, but evidence suggests that these agents might induce an immune-suppressive systemic immune response, indicated by increased expression of inhibitory checkpoint molecules such as programmedcelldeath 1ligand 1 and 2, and that these changes could be associated with clinical response. Different radiotherapy modalities can induce distinct immune profiles, which can either activate or suppress immune-mediated tumour killing and the current preclinical models used for prostate cancer research are not yet optimal for studying the complexity of the radiotherapy-induced immune response.

Loss of Lkb1 cooperates with BrafV600E and ultraviolet radiation, increasing melanoma multiplicity and neural-like dedifferentiation.

The mechanisms that work alongside BRAFV600E oncogene in melanoma development, in addition to ultraviolet (UV) radiation (UVR), are of great interest. Analysis of human melanoma tumors [data from The Cancer Genome Atlas (TCGA)] revealed that 50% or more of the samples expressed no or low amounts of serine/threonine protein kinase STK11 (also known as LKB1) protein. Here, we report that, in a mouse model, concomitant neonatal BrafV600E activation and Lkb1 tumor suppressor ablation in melanocytes led to full melanoma development. A single postnatal dose of UVB radiation had no effect on melanoma onset in Lkb1-depleted mice compared with BrafV600E-irradiated mice, but increased tumor multiplicity. In concordance with these findings and previous reports, Lkb1-null irradiated mice exhibited deficient DNA damage repair (DDR). Histologically, tumors lacking Lkb1 were enriched in neural-like tumor morphology. Genetic profiling and gene set enrichment analyses of tumor sample mutated genes indicated that loss of Lkb1 promoted the selection of altered genes associated with neural differentiation processes. Thus, these results suggest that the loss of Lkb1 cooperates with BrafV600E and UVR, impairing the DDR and increasing melanoma multiplicity and neural-like dedifferentiation.

A single dose of radiation elicits comparable acute salivary gland injury to fractionated radiation.

The salivary glands are often damaged during head and neck cancer radiotherapy. This results in chronic dry mouth, which adversely affects quality of life and for which there is no long-term cure. Mouse models of salivary gland injury are routinely used in regenerative research. However, there is no clear consensus on the radiation regime required to cause injury. Here, we analysed three regimes of γ-irradiation of the submandibular salivary gland. Transcriptional analysis, immunofluorescence and flow cytometry was used to profile DNA damage, gland architecture and immune cell changes 3 days after single doses of 10 or 15 Gy or three doses of 5 Gy. Irrespective of the regime, radiation induced comparable levels of DNA damage, cell cycle arrest, loss of glandular architecture, increased pro-inflammatory cytokines and a reduction in tissue-resident macrophages, relative to those observed in non-irradiated submandibular glands. Given these data, coupled with the fact that repeated anaesthetic can negatively affect animal welfare and interfere with saliva secretion, we conclude that a single dose of 10 Gy irradiation is the most refined method of inducing acute salivary gland injury in a mouse model.

Uncovering the connection between Ly6ChiCD103+ myeloid cells and radiation-induced cardiac fibrosis by CyTOF

Several immune cell populations participate in the development of radiation-induced cardiac fibrosis. However, the underlying mechanism remains to be elucidated. Male C57BL/6 mice (8–12 weeks old) were anesthetized and exposed to a single cardiac radiation dose of 20 Gy using the small-animal radiation research platform. We conducted echocardiography and histological analysis to identify cardiac fibrosis from a functional and pathological perspective. Time-of-flight mass cytometry (CyTOF) was used to describe the compositional changes of immune cells 1, 4, and 8 weeks after cardiac irradiation in mouse peripheral blood and cardiac tissue samples. Real-time quantitative polymerase chain reaction (RT-qPCR) was used to measure CD14 and CD105 mRNA levels from peripheral blood cells in eight patients who received thoracic radiotherapy 6 months ago. We observed reduced cardiac systolic function and increased collagen deposition in cardiac tissue after irradiation. Transforming growth factor-β, tumor necrosis factor-α, and interleukin-6 expression significantly elevated in the plasma. We identified a significant increase in CD45+ immune cell levels four weeks after cardiac irradiation using CyTOF, and neutrophil, monocyte, and macrophage levels elevated in blood samples after cardiac irradiation (four weeks). In cardiac tissue samples, monocyte and macrophage levels increased after cardiac irradiation (four weeks) compared with control group. Macrophages and monocytes were further analyzed, and the proportion of Ly6ChiCD103+ myeloid cells increased after cardiac irradiation in tissue samples (four weeks). RT-qPCR revealed that CD14 expression was higher in patients with cardiac injured group than in the control group (Previous studies reported that Ly6Chi monocytes in mice are similar to CD14 + CD16− monocytes in humans). We found that Ly6ChiCD103+ myeloid cells are critical subsets in radiation-induced cardiac fibrosis and might play protective roles in the process. Ly6ChiCD103+ myeloid cells may be considered an early biomarker for detecting radiation-induced cardiac fibrosis.

Multi-omics analysis to evaluate the effects of solar exposure and a broad-spectrum SPF50+ sunscreen on markers of skin barrier function in a skin ecosystem model.

Sun exposure induces major skin alterations, but its effects on skin metabolites and lipids remain largely unknown. Using an original reconstructed human epidermis (RHE) model colonized with human microbiota and supplemented with human sebum, we previously showed that a single dose of simulated solar radiation (SSR) significantly impacted the skin metabolome and microbiota. In this article, we further analyzed SSR-induced changes on skin metabolites and lipids in the same RHE model. Among the significantly altered metabolites (log2-fold changes with p ≤ 0.05), we found several natural moisturizing factors (NMFs): amino acids, lactate, glycerol, urocanic acid, pyrrolidone carboxylic acid and derivatives. Analyses of the stratum corneum lipids also showed that SSR induced lower levels of free fatty acids and higher levels of ceramides, cholesterols and its derivatives. An imbalance in NMFs and ceramides combined to an increase of proinflammatory lipids may participate in skin permeability barrier impairment, dehydration and inflammatory reaction to the sun. Our skin model also allowed the evaluation of an innovative ultraviolet/blue light (UV/BL) broad-spectrum sunscreen with a high sun protection factor (SPF50+). We found that using this sunscreen prior to SSR exposure could in part prevent SSR-induced alterations in NMFs and lipids in the skin ecosystem RHE model.

FLASH proton reirradiation, with or without hypofractionation, mitigates chronic toxicity in the normal murine intestine, skin, and bone.

The normal tissue sparing afforded by FLASH radiotherapy (RT) is being intensely investigated for potential clinical translation. Here, we studied the effects of FLASH proton RT (F-PRT) in the reirradiation setting, with or without hypofractionation. Chronic toxicities in three murine models of normal tissue toxicity including the intestine, skin, and bone were investigated. In studies of the intestine, single-dose irradiation was performed with 12 Gy of Standard proton RT (S-PRT), followed by a second dose of 12 Gy of F-PRT or S-PRT. Additionally, a hypofractionation scheme was applied in the reirradiation setting (3 x 6.4 Gy of F-PRT or S-PRT, given every 48 hrs). In studies of skin/bone of the murine leg, 15 Gy of S-PRT was followed by hypofractionated reirradiation with F-PRT or S-PRT (3 x 11 Gy). Compared to reirradiation with S-PRT, F-PRT reduced intestinal fibrosis and collagen deposition in the reirradiation setting and significantly increased survival rate, demonstrating its protective effects on intestinal tissues. In previously irradiated leg tissues, reirradiation with hypofractionated F-PRT created transient dermatitis that fully resolved in contrast to reirradiation with hypofractionated S-PRT. Lymphedema was also alleviated after a second course of radiation with F-PRT, along with significant reductions in the accumulation of fibrous connective tissue in the skin compared to mice reirradiated with S-PRT. The delivery of a second course of fractionated S-PRT induced tibial fractures in 83.3% of the mice, whereas only 20% of mice reirradiated with F-PRT presented with fractures. These studies provide the first evidence of the sparing effects of F-PRT, in the setting of hypofractionated reirradiation. The results support FLASH as highly relevant to the reirradiation regimen where it exhibits significant potential to minimize chronic complications for patients undergoing RT.

A comparison of ultrasound volume navigation, O-arm navigation, and X-ray guidance for screw placement in minimally invasive transforaminal lumbar interbody fusion: a randomized controlled trial.

To compare the differences between Ultrasound Volume Navigation (UVN), O-arm Navigation, and conventional X-ray fluoroscopy-guided screw placement in Minimally Invasive Transforaminal Lumbar Interbody Fusion (MIS-TLIF) surgeries. A total of 90 patients who underwent MIS-TLIF due to lumbar disc herniation from January 2022 to January 2023 were randomly assigned to the UVN group, O-arm group, and X-ray group. UVN, O-arm navigation, and X-ray guidance were used for screw placement in the respective groups, while the remaining surgical procedures followed routine MIS-TLIF protocols. Intraoperative data including average single screw placement time, total radiation dose, and average effective radiation dose per screw were recorded and calculated. On the 10th day after surgery, postoperative X-ray and CT examinations were conducted to assess screw placement accuracy and facet joint violation. There were no significant differences in general characteristics among the three groups, ensuring comparability. Firstly, the average single screw placement time in the O-arm group was significantly shorter than that in the UVN group and X-ray group (P<0.05). Secondly, in terms of total radiation dose during surgery, for single-level MIS-TLIF, the O-arm group had a significantly higher radiation dose compared to the UVN group and X-ray group (P<0.05). However, for multi-level MIS-TLIF, the X-ray group had a significantly higher radiation dose than the O-arm group and UVN group (P<0.05). In terms of average single screw radiation dose, the O-arm group and X-ray group were similar (P>0.05), while the UVN group was significantly lower than the other two groups (P<0.05). Furthermore, no significant differences were found in screw placement assessment grades among the three groups (P>0.05). However, in terms of facet joint violation rate, the UVN group (10.3%) and O-arm group (10.7%) showed no significant difference (P>0.05), while the X-ray group (26.7%) was significantly higher than both groups (P<0.05). Moreover, in the UVN group, there were significant correlations between average single screw placement time and placement grade with BMI index (r = 0.637, P<0.05; r = 0.504, P<0.05), while no similar significant correlations were found in the O-arm and X-ray groups. UVN-guided screw placement in MIS-TLIF surgeries demonstrates comparable efficiency, visualization, and accuracy to O-arm navigation, while significantly reducing radiation exposure compared to both O-arm navigation and X-ray guidance. However, UVN may be influenced by factors like obesity, limiting its application.

Cerium oxide nanoparticles display antioxidant and antiapoptotic effects on gamma irradiation-induced hepatotoxicity.

Throughout radiotherapy, radiation of the hepatic tissue leads to damage of the hepatocytes. We designed the current study to examine how cerium oxide nanoparticles (CONPs) modulate gamma irradiation-induced hepatotoxicity in rats. Animals received CONPs (15 mg/kg body weight [BW], ip) single daily dose for 14 days, and they were exposed on the seventh day to a single dose of gamma radiation (6 Gy). Results showed that irradiation increased serum aspartate aminotransferase, alanine aminotransferase, and alkaline phosphatase activities. Furthermore, it elevated oxidative stress biomarker; malondialdehyde (MDA) and inhibited the activities of antioxidant enzymes (superoxide dismutase and glutathione peroxidase) in hepatic tissues homogenate. Additionally, hepatic apoptotic markers; caspase-3 (Casp-3) and Casp-9 were elevated and the B-cell lymphoma-2 (Bcl-2) gene level was decreased in rats exposed to radiation dose. We observed that CONPs can modulate these changes, where CONPs reduced liver enzyme activities, MDA, and apoptotic markers levels, in addition, it elevated antioxidant enzyme activities and Bcl-2 gene levels, as well as improved histopathological changes in the irradiated animals. So our results concluded that CONPs had the ability to act as radioprotector defense against hepatotoxicity resulted during radiotherapy.

Radiation-Induced DNA Damage in Uveal Melanoma Is Influenced by Dose Delivery and Chromosome 3 Status.

The purpose of this study was to analyze the extent of DNA breaks in primary uveal melanoma (UM) with regard to radiotherapy dose delivery (single-dose versus fractionated) and monosomy 3 status. A total of 54 patients with UM were included. Stereotactic radiotherapy (SRT) was performed in 23 patients, with 8 undergoing single-dose SRT (sdSRT) treatment and 15 receiving fractionated SRT (fSRT). DNA breaks in the enucleated or endoresected tumors were visualized by a TUNEL assay and quantified by measuring the TUNEL-positive area. Protein expression was analyzed by immunohistochemistry. Co-detection of chromosome 3 with proteins was performed by immuno-fluorescent in situ hybridization. The amount of DNA breaks in the total irradiated group was increased by 2.7-fold (P < 0.001) compared to non-irradiated tissue. Tumors treated with fSRT were affected more severely, showing 2.1-fold more DNA damage (P = 0.007) compared to the cases after single (high) dose irradiation (sdSRT). Monosomy 3 tumors showed less DNA breaks compared to disomy 3 samples (P = 0.004). The presence of metastases after radiotherapy correlated with monosomy 3 and less DNA breaks compared to patients with non-metastatic cancer in the combined group with fSRT and sdSRT (P < 0.05). Fractionated irradiation led to more DNA damage than single-dose treatment in primary UM. As tumors with monosomy 3 showed less DNA breaks than those with disomy 3, this may indicate that they are less radiosensitive, which may influence the efficacy of irradiation.

Stereotactic Radiosurgery with Volumetric Modulated Arc Radiotherapy: Final Results of a Multi-arm Phase I Trial (DESTROY-2)

AimsTo present the final results of a phase I trial on stereotactic radiosurgery (SRS) delivered using volumetric modulated arc therapy (VMAT) in patients with primary or metastatic tumors in different extracranial sites. Materials and methodsThe DESTROY-2 trial, planned as a prospective dose escalation study in oligometastatic (one to five lesions) cancer patients relied on the delivery of a single high dose of radiation utilizing high-precision technology. The primary study endpoint was the definition of the maximum tolerated dose (MTD) of SRS-VMAT. The secondary objectives of the study were the evaluation of safety, efficacy, and long-term outcomes. All patients consecutively observed at our radiotherapy unit matching the inclusion criteria were enrolled. Each enrolled subject was included in a different phase I study arm, depending on the tumor site and the disease stage (lung, liver, bone, other), and sequentially assigned to a particular dose level. ResultsTwo hundred twenty seven lesions in 164 consecutive patients (male/female: 97/67, median age: 68 years; range: 29–92) were treated. The main primary tumors were: prostate cancer (60 patients), colorectal cancer (47 patients), and breast cancer (39 patients). The maximum planned dose level was achieved in all study arms, and the MTD was not exceeded. 34 Gy, 32 Gy, 24 Gy, and 24 Gy were established as the single-fraction doses for treating lung, liver, bone, and other extracranial lesions, respectively. The prescribed BED 2Gyα/β:10 to the planning target volume ranged from 26.4 Gy to 149.6 Gy. Twenty-seven patients (16.5%) experienced grade 1–2 and only one grade 3 acute toxicity, which was a pulmonary one. In terms of late toxicity, we registered only 5 toxicity>G2: a G3 gastro-intestinal one, three G3 bone toxicity, and a G3 laryngeal toxicity. The overall response was available for 199 lesions: 107 complete response (53.8%), 50 partial response (25.1%), and 31 stable disease (15.6%), leading to an overall response rate of 94.5%. Progression was registered only in 11 cases (5.5%). The overall response rate in each arm ranged from 88.6% to 96.4%. The overall two-year local control, distant metastasis free survival, disease free survival, and overall survival were 81.7%, 33.0%, 25.4%, and 78.7% respectively. ConclusionIn conclusion, the planned doses of 34 Gy, 32 Gy, 24 Gy, and 24 Gy were successfully administered as single-fractions for the treatment of lung, liver, bone, and other extracranial lesions, respectively, in a prospective SRS dose-escalation trial. No dose-limiting toxicities were registered, and minimal acute and late toxicity were reported. New indications for SRS are currently being studied in oligoprogressive patients receiving targeted drugs or in combination with immunotherapy. The DESTROY-2 trial represents, in our opinion, a credible starting point for future modern radiosurgery trials.

Retrospective study on the profile of patients undergoing intraoperative radiotherapy with INTRABEAM for breast cancer treatment at a Brazilian cancer center.

e12538 Background: Conservative breast therapy combined with adjuvant radiotherapy has been the preferred treatment for early-stage breast cancer for many decades. Considering that most breast cancer recurrences occur near the original tumor site, partial breast radiotherapy has become an alternative for patients in this scenario, allowing for a single-dose radiation application directly to the tumor site. This technique has advantages such as reducing local toxicity and improving the quality of life for treated patients, in addition to decreasing the waiting time for radiotherapy treatment in developing countries like ours. Our case series is the largest in Latin America to date, and we believe that reporting the results of our experience will be valuable for the scientific community and aid in treatment decision-making in low- and middle-income countries. Methods: This is a retrospective study based on data from the medical records of 209 patients with early-stage breast cancer undergoing conservative surgery and intraoperative radiotherapy at A.C. Camargo Cancer Center (São Paulo, Brazil) from 2016 to 2023. Results: In our cohort, 88.5% of tumors were invasive ductal carcinomas. The majority were T1b (41.8%), had histological grade 2 (45.4%), nuclear grade 2 (62.7%), and showed no axillary involvement (87.6%). All patients received intraoperative radiotherapy in a single dose of 20 Gy radiation at the tumor site with a voltage of 50 kV. In our study, 17.7% of patients required additional external radiotherapy due to postoperative histopathological findings inconsistent with treatment indication criteria, including 35.3% for micrometastasis and 32.4% for nodal macrometastasis, 10.8% for narrow or compromised margins, 10.8% for histological types not covered in the final report, 2.7% for multifocality, 2.7% for extensive ductal carcinoma in situ, 2.7% for negative progesterone receptor, and 2.7% for the presence of lymphatic vascular invasion. The average follow-up time for patients was 36 months. The local recurrence rate was 0.5%. Conclusions: The results of this study support established data indicating the efficacy of intraoperative radiotherapy in early-stage breast cancer treatment. Therefore, for carefully selected patients, this technique with should be considered as a treatment option. We will continue to follow this patient cohort to identify the occurrence of late recurrences and publish long-term follow-up data.

Combination of proton- or X-irradiation with anti-PDL1 immunotherapy in two murine oral cancers

Combining radiation therapy with immunotherapy is a strategy to improve both treatments. The purpose of this study was to compare responses for two syngeneic head and neck cancer (HNC) tumor models in mice following X-ray or proton irradiation with or without immune checkpoint inhibition (ICI). MOC1 (immunogenic) and MOC2 (less immunogenic) tumors were inoculated in the right hind leg of each mouse (C57BL/6J, n = 398). Mice were injected with anti-PDL1 (10 mg/kg, twice weekly for 2 weeks), and tumors were treated with single-dose irradiation (5–30 Gy) with X-rays or protons. MOC2 tumors grew faster and were more radioresistant than MOC1 tumors, and all mice with MOC2 tumors developed metastases. Irradiation reduced the tumor volume in a dose-dependent manner. ICI alone reduced the tumor volume for MOC1 with 20% compared to controls, while no reduction was seen for MOC2. For MOC1, there was a clear treatment synergy when combining irradiation with ICI for radiation doses above 5 Gy and there was a tendency for X-rays being slightly more biologically effective compared to protons. For MOC2, there was a tendency of protons being more effective than X-rays, but both radiation types showed a small synergy when combined with ICI. Although the responses and magnitudes of the therapeutic effect varied, the optimal radiation dose for maximal synergy appeared to be in the order of 10–15 Gy, regardless of tumor model.

Abstract PS01-09: Early Results of a Phase I Pre-Operative Single Fraction Ablative Trial for Early Stage Breast Cancer

Abstract Objective(s): To explore the impact of pre-operative single fraction stereotactic ablative partial breast irradiation (SPBI) dose escalation (30, 34, or 38Gy) on toxicity and tumor response for early-stage hormone receptor (HR)+ breast cancer in an interim analysis of an expanded cohort phase I dose escalation study (NCT04040569). Methods: Eligible patients (pts) have &amp;lt; 3 cm, HR+, Her2 -, cN0 invasive breast carcinomas not requiring chemotherapy. Patients are treated on either MR LINAC, robotic radiosurgery, or cobalt stereotactic breast units. Endocrine therapy is started two weeks after SPBI. Surgery is completed 2-12 months after SPBI. The primary objective is to escalate single fraction SPBI to an ablative dose without exceeding maximum tolerable dose (MTD). Secondary endpoints include pathologic complete response (pCR), local control, toxicity, cosmesis, and distant disease-free survival. Near complete response (nCR) is defined as RCB 1 and Miller-Payne 4/5. Dose limiting toxicity (DLT) is defined as grade ≥3 toxicity or any grade 4/5 toxicity attributed to SPBI. Each dose cohort enrolls 7-15 pts. Dose escalation is permitted if 0/7, 2/9, ≤3/12, or ≤4/15 patients experienced a DLT within 90 days of SPBI. MTD is exceeded if more DLTs occur in any cohort. Results: From 12/2019 to 6/2023, 11 and 15 pts were treated with 30Gy and 34Gy, respectively. Rates of pCR/nCR are 37.5% for 30Gy versus 92.8% 34 Gy (p=0.01). At 30Gy, 8/11 pts (73%) underwent surgery with a median 4.3 (range 2.8-5.9) month interval from SPBI to surgery: 0/8 (0%) had a pCR and 3/8 (37.5%) had a nCR. At dose level 34Gy, 14/15 pts (93%) underwent surgery with a median 7.3 (range 5.9-12) month interval from SPBI to surgery: 6/14 (42.8%) had a pCR while 7/14 (50%) had a nCR. Of the 8 pts with a nCR, 50% had only 1-3mm of residual disease. The mean ki67 for the entire cohort was 12.0% +/- 6.9% at diagnosis and decreased to 1.4 +/-2.3% at surgery. 13/14 (92.8%) pts with residual disease had a ki67 &amp;lt; 3% after surgery and SPBI. There were 33 acute grade 1; 2 acute grade 2 (breast pain and dermatitis); and 10 late grade 1 [1 grade 2 (breast pain), and 1 grade 3 (slow healing wound) in an uncontrolled diabetic] toxicities. Conclusion: First study to show pre-operative SPBI up to 34Gy in a single fraction was safe and effective for early-stage HR+ breast cancer. Escalating the dose has achieved a dramatic improvement in pCR/nCR (92.8%) suggesting this is an exciting approach for potentially eliminating tumor with radiation/endocrine therapy alone in early stage breast cancer and potentially paving a path towards non-surgical management in highly selected patients. Citation Format: Asal Rahimi, A Marilyn Leitch, Baṣak Dogan, Prasanna Alluri, Deborah Farr, Mona Arbab, Stephen Seiler, Nathan Kim, Rachel Wooldridge, Nisha Unni, Chika Nwachukwu, Ina Patel, You Zhang, David Parsons, Anvy Nguyen, Howard E Morgan, Heather McArthur, Sunati Sahoo, Robert Timmerman. Early Results of a Phase I Pre-Operative Single Fraction Ablative Trial for Early Stage Breast Cancer [abstract]. In: Proceedings of the 2023 San Antonio Breast Cancer Symposium; 2023 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2024;84(9 Suppl):Abstract nr PS01-09.