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The ultimate goal of radiation oncology is to eradicate tumours without toxicity to non-malignant tissues. FLASH radiotherapy, or the delivery of ultra-high dose rates of radiation (>40 Gy/s), emerged as a modality of irradiation that enables tumour control to be maintained while reducing toxicity to surrounding non-malignant tissues. In the past few years, preclinical studies have shown that FLASH radiotherapy can be delivered in very short times and substantially can widen the therapeutic window of radiotherapy. This ultra-fast radiation delivery could reduce toxicity and thus enable dose escalation to enhance antitumour efficacy, with the additional benefits of reducing treatment time and organ motion-related issues, eventually increasing the number of patients who can be treated. At present, FLASH is recognized as one of the most promising breakthroughs in radiation oncology, standing at the crossroads between technology, physics, chemistry and biology; however, several hurdles make its clinical translation difficult, including the need for a better understanding of the biological mechanisms, optimization of parameters and technological challenges. In this Perspective, we provide an overview of the principles underlying FLASH radiotherapy and discuss the challenges along the path towards its clinical application.FLASH radiotherapy involves delivering ultra-high dose rates of radiation, which enables sustained tumour control with reduced toxicity to surrounding tissues. The authors of this Perspective describe the principles underlying FLASH radiotherapy, present the available evidence from preclinical studies testing this modality and discuss the challenges for its application in routine clinical practice.

Ferroptosis, a form of regulated cell death caused by lipid peroxidation, was recently identified as a natural tumor suppression mechanism. Here, we show that ionizing radiation (IR) induces ferroptosis in cancer cells. Mechanistically, IR induces not only reactive oxygen species (ROS) but also the expression of ACSL4, a lipid metabolism enzyme required for ferroptosis, resulting in elevated lipid peroxidation and ferroptosis. ACSL4 ablation largely abolishes IR-induced ferroptosis and promotes radioresistance. IR also induces the expression of ferroptosis inhibitors, including SLC7A11 and GPX4, as an adaptive response. IR- or KEAP1 deficiency-induced SLC7A11 expression promotes radioresistance through inhibiting ferroptosis. Inactivating SLC7A11 or GPX4 with ferroptosis inducers (FINs) sensitizes radioresistant cancer cells and xenograft tumors to IR. Furthermore, radiotherapy induces ferroptosis in cancer patients, and increased ferroptosis correlates with better response and longer survival to radiotherapy in cancer patients. Our study reveals a previously unrecognized link between IR and ferroptosis and indicates that further exploration of the combination of radiotherapy and FINs in cancer treatment is warranted.

The past three decades have borne witness to many advances in the understanding of the molecular biology and treatment of nasopharyngeal carcinoma (NPC), an Epstein–Barr virus (EBV)-associated cancer endemic to southern China, southeast Asia and north Africa. In this Review, we provide a comprehensive, interdisciplinary overview of key research findings regarding NPC pathogenesis, treatment, screening and biomarker development. We describe how technological advances have led to the advent of proton therapy and other contemporary radiotherapy approaches, and emphasize the relentless efforts to identify the optimal sequencing of chemotherapy with radiotherapy through decades of clinical trials. Basic research into the pathogenic role of EBV and the genomic, epigenomic and immune landscape of NPC has laid the foundations of translational research. The latter, in turn, has led to the development of new biomarkers and therapeutic targets and of improved approaches for individualizing immunotherapy and targeted therapies for patients with NPC. We provide historical context to illustrate the effect of these advances on treatment outcomes at present. We describe current preclinical and clinical challenges and controversies in the hope of providing insights for future investigation.Nasopharyngeal carcinoma (NPC) is an Epstein–Barr virus (EBV)-associated malignancy endemic to southern China, southeast Asia and north Africa. The authors of this Review present a comprehensive overview of advances from the past three decades on the pathogenic role of EBV, and the genomic, epigenomic and immune landscape of NPC, which have led to the development of new biomarkers, therapeutic targets and improved treatment approaches for patients with NPC.

Radiopharmaceutical therapy (RPT) is emerging as a safe and effective targeted approach to treating many types of cancer. In RPT, radiation is systemically or locally delivered using pharmaceuticals that either bind preferentially to cancer cells or accumulate by physiological mechanisms. Almost all radionuclides used in RPT emit photons that can be imaged, enabling non-invasive visualization of the biodistribution of the therapeutic agent. Compared with almost all other systemic cancer treatment options, RPT has shown efficacy with minimal toxicity. With the recent FDA approval of several RPT agents, the remarkable potential of this treatment is now being recognized. This Review covers the fundamental properties, clinical development and associated challenges of RPT.Radiopharmaceutical therapy is emerging as a safe and effective approach for the treatment of cancer, offering several advantages over existing therapeutic strategies. Here, Sgouros and colleagues provide an overview of the fundamental properties of radiopharmaceutical therapy, discuss agents in use and in clinical development and highlight the associated translational challenges.

A variety of targeted anticancer agents have been successfully introduced into clinical practice, largely reflecting their ability to inhibit specific molecular alterations that are required for disease progression. However, not all malignant cells rely on such alterations to survive, proliferate, disseminate and/or evade anticancer immunity, implying that many tumours are intrinsically resistant to targeted therapies. Radiotherapy is well known for its ability to activate cytotoxic signalling pathways that ultimately promote the death of cancer cells, as well as numerous cytoprotective mechanisms that are elicited by cellular damage. Importantly, many cytoprotective mechanisms elicited by radiotherapy can be abrogated by targeted anticancer agents, suggesting that radiotherapy could be harnessed to enhance the clinical efficacy of these drugs. In this Review, we discuss preclinical and clinical data that introduce radiotherapy as a tool to elicit or amplify clinically actionable signalling pathways in patients with cancer.Targeted therapies have improved the outcomes of many patients with cancer, although many more lack targetable alterations or do not derive clinical benefit for other reasons. Radiotherapy can also provide benefit to many patients, although radioresistance often limits the effectiveness of this intervention. Here, the authors describe the potential for radiotherapy to promote non-oncogene dependence on targetable signalling pathways, thus extending the benefits of both targeted therapy and radiotherapy to greater numbers of patients.

Key Points Radiotherapy has proven potential to cure tumours by eradicating cancer stem cells. Current state-of-the-art techniques of photon-based radiotherapy are approaching the physical limits of shaping high doses to the target volume. Particle therapy reduces the volume of normal tissues irradiated with low or intermediate radiation doses and has the potential to reduce side effects in normal tissue as well as to escalate doses to radioresistant tumours. Photon and especially particle radiotherapy will benefit from further improvements to image guidance with full adaptation of dose delivery to motion and anatomical changes of tumours and normal tissues during treatment. Treatment planning algorithms that enable much faster planning and replanning, include uncertainties to improve robustness and enable optimization of multi-objective planning or plan comparison are on the verge of widespread clinical implementation. The basic biological mechanisms of radiosensitivity and radioresistance are known and part of today's population-based treatment strategies. Biomarkers and bio-imaging that enable mechanisms of radioresistance to be assessed in individual tumours and normal tissues are rapidly emerging. Biomarkers have unexplored potential for predicting the extent of subclinical spread of tumour cells to help define the clinical target volume. Biomarkers, when integrated into treatment planning, may potentiate the degree of personalization of radiotherapy that is already achieved today on a technological basis. Radiation oncology has high potential to showcase the efficacy of precision medicine in oncology. This Review discusses technological and biologically based advances in radiotherapy. The authors envisage that these two major strategies will act synergistically to further widen the therapeutic window of radiation oncology in the era of precision medicine. Technological advances and clinical research over the past few decades have given radiation oncologists the capability to personalize treatments for accurate delivery of radiation dose based on clinical parameters and anatomical information. Eradication of gross and microscopic tumours with preservation of health-related quality of life can be achieved in many patients. Two major strategies, acting synergistically, will enable further widening of the therapeutic window of radiation oncology in the era of precision medicine: technology-driven improvement of treatment conformity, including advanced image guidance and particle therapy, and novel biological concepts for personalized treatment, including biomarker-guided prescription, combined treatment modalities and adaptation of treatment during its course.

MRI can help to categorize tissues as malignant or non-malignant both anatomically and functionally, with a high level of spatial and temporal resolution. This non-invasive imaging modality has been integrated with radiotherapy in devices that can differentially target the most aggressive and resistant regions of tumours. The past decade has seen the clinical deployment of treatment devices that combine imaging with targeted irradiation, making the aspiration of integrated MRI-guided radiotherapy (MRIgRT) a reality. The two main clinical drivers for the adoption of MRIgRT are the ability to image anatomical changes that occur before and during treatment in order to adapt the treatment approach, and to image and target the biological features of each tumour. Using motion management and biological targeting, the radiation dose delivered to the tumour can be adjusted during treatment to improve the probability of tumour control, while simultaneously reducing the radiation delivered to non-malignant tissues, thereby reducing the risk of treatment-related toxicities. The benefits of this approach are expected to increase survival and quality of life. In this Review, we describe the current state of MRIgRT, and the opportunities and challenges of this new radiotherapy approach.In the past decade, treatment devices that combine imaging with targeted irradiation have been developed to deliver MRI-guided radiotherapy (MRIgRT). This treatment modality uses motion management and biological targeting to improve local control rates whilst reducing the radiation delivered to non-malignant tissues. The authors of this Review describe the current state of MRIgRT, and the opportunities and challenges of this radiotherapy approach.

More than 60 years ago, the effect whereby radiotherapy at one site may lead to regression of metastatic cancer at distant sites that are not irradiated was described and called the abscopal effect (from 'ab scopus', that is, away from the target). The abscopal effect has been connected to mechanisms involving the immune system. However, the effect is rare because at the time of treatment, established immune-tolerance mechanisms may hamper the development of sufficiently robust abscopal responses. Today, the growing consensus is that combining radiotherapy with immunotherapy provides an opportunity to boost abscopal response rates, extending the use of radiotherapy to treatment of both local and metastatic disease. In this Opinion article, we review evidence for this growing consensus and highlight emerging limitations to boosting the abscopal effect using immunotherapy. This is followed by a perspective on current and potential cross-disciplinary approaches, including the use of smart materials to address these limitations.

Key Points Radiotherapy is a common treatment option for cancer patients. However, many aspects of the tumour microenvironment (TME) can render a tumour resistant to radiotherapy de novo or can lead it to recur with a worse prognosis following therapy. Normal tissue toxicity limits the dose of radiotherapy that can be safely delivered. Combination strategies are required in order to achieve better tumour control. Radiotherapy-mediated immunogenic cell death (ICD) can elicit an immune response, but antitumour immunity may be limited owing to the presence of radioresistant suppressor cell types in the TME. Combining radiotherapy and immunomodulatory treatments may overcome adaptive immune suppression and holds great promise both locally in the primary tumour and abscopally. Hypoxia has a crucial role in radioresistance owing to reduced oxygen-mediated fixation of DNA damage and hypoxia induced factor 1α (HIF1α)-mediated cell survival. Attempts to increase oxygen delivery, normalize tumour vessels, inhibit HIF1α and prevent the recruitment of bone marrow-derived cells (BMDCs) required for vasculogenesis are all being tested to reduce tumour hypoxia, improve radiotherapy responses and prevent tumour recurrence after therapy. Tumour irradiation induces a wound healing response that is characterized by inflammation, cancer-associated fibroblast (CAF) modulation and extracellular matrix (ECM) remodelling, which may facilitate tumour recurrence. Targeting the initial inflammatory response may counteract attempts to boost the immune-mediated antitumour response following radiotherapy. Therefore, reducing ECM remodelling by inhibiting growth factors, receptor kinases or matrix enzymes may be more effective in preventing the post-irradiation stiffening of the TME that could facilitate tumour spread. Careful scheduling of tumour reoxygenation strategies with radiotherapy will be required to maximize tumour control. Subsequent inclusion of immunomodulatory and anti-fibrotic treatments should be considered to maximize therapeutic benefits and to prevent post-irradiation tumour recurrence and metastasis. In this Review, Barker and colleagues describe the mechanisms of radioresistance that are mediated by the tumour stroma and explore how these mechanisms can be targeted to improve radiotherapy responses. Radiotherapy plays a central part in curing cancer. For decades, most research on improving treatment outcomes has focused on modulating radiation-induced biological effects on cancer cells. Recently, we have better understood that components within the tumour microenvironment have pivotal roles in determining treatment outcomes. In this Review, we describe vascular, stromal and immunological changes that are induced in the tumour microenvironment by irradiation and discuss how these changes may promote radioresistance and tumour recurrence. We also highlight how this knowledge is guiding the development of new treatment paradigms in which biologically targeted agents will be combined with radiotherapy.

Head and neck cancers are a heterogeneous collection of malignancies of the upper aerodigestive tract, salivary glands and thyroid. In this Review, we primarily focus on the changing therapeutic landscape of head and neck squamous cell carcinomas (HNSCCs) that can arise in the oral cavity, oropharynx, hypopharynx and larynx. We highlight developments in surgical and non-surgical therapies (mainly involving the combination of radiotherapy and chemotherapy), outlining how these treatments are being used in the current era of widespread testing for the presence of human papillomavirus infection in patients with HNSCC. Finally, we describe the clinical trials that led to the approval of the first immunotherapeutic agents for HNSCC, and discuss the development of strategies to decrease the toxicity of different treatment modalities.The authors of this Review discuss treatments currently available for patients with head and neck squamous cell carcinomas (focusing in those of the oral cavity, oropharynx, hypopharynx and larynx). Advances in surgical and non-surgical approaches (mainly combinations of radiotherapy and chemotherapy) are discussed, including the first immunotherapeutic agents approved for these malignancies.