What Is Radiation Oncology? Research Areas, Funding, and Career Paths

This page is an educational overview of a research and clinical field. It is not medical advice and does not describe how any individual patient should be treated.

Radiation oncology is the branch of medicine and biomedical science that uses ionizing radiation to treat cancer and, less often, certain non-malignant conditions. Treatment, usually called radiation therapy or radiotherapy, works by delivering a carefully planned dose of radiation to a defined target so that the cancer cells there are damaged beyond repair while the surrounding normal tissue is spared as far as possible. The physicians who direct this work are radiation oncologists. They work in a team with medical physicists, dosimetrists, radiation therapists, nurses, and the medical and surgical oncologists who treat the same patients with drugs and operations.

As a research field, radiation oncology sits at an unusual intersection. It is a clinical specialty, but it also draws on physics (how radiation is produced, shaped and measured), radiation biology (how cells and tissues respond), engineering and computing (treatment machines, imaging, planning software and, increasingly, machine learning), and clinical trial science. This guide explains what the field covers, its main techniques and subspecialties, how its research is organized and funded, which societies and journals shape it, how radiation safety touches research work, and how people train for careers in it. Terms such as radiology and radiotherapy are often confused, so the FAQ at the end sets out the differences.

What Radiation Oncology Covers

The core question of the field is the therapeutic ratio: how much tumour control can be achieved for an acceptable risk of damage to healthy tissue. Almost every research programme in radiation oncology is, in some way, an attempt to widen that ratio. There are three broad ways to do it:

• Deliver the dose more precisely. Better imaging, better treatment planning and better machines let the high-dose region conform more tightly to the target.
• Change how the dose is given. Fractionation (the number and size of treatment sessions), total dose, and the timing of treatment relative to other therapies can all change the balance between tumour effect and normal-tissue effect.
• Change the biology. Combining radiation with drugs that sensitize tumour cells, protect normal tissue, or engage the immune system is a major area of translational research.

Radiation is used with different goals. Curative treatment aims to eradicate a localized cancer, sometimes alone and sometimes combined with surgery or systemic therapy. Adjuvant or neoadjuvant treatment is given after or before surgery to lower the chance of recurrence or to make an operation easier. Palliative treatment aims to relieve symptoms such as pain from bone metastases or obstruction, usually with shorter courses. Each setting generates its own research questions and its own trial endpoints.

Main Treatment Approaches

External beam radiotherapy

The most common form is external beam radiotherapy, in which a machine outside the body directs radiation at the target. The workhorse is the medical linear accelerator, which produces high-energy X-ray (photon) beams and electron beams and has been the standard clinical machine since the second half of the twentieth century. Modern delivery techniques build on it: intensity-modulated radiotherapy (IMRT) and volumetric modulated arc therapy shape the dose with great precision; image-guided radiotherapy (IGRT) uses imaging at the treatment machine to verify target position before and during treatment; and stereotactic techniques, such as stereotactic radiosurgery for the brain and stereotactic body radiotherapy (SBRT, also called SABR) for tumours elsewhere, deliver a small number of very high-dose fractions with tight margins. The adoption and optimal use of these techniques has been the subject of a long sequence of clinical trials.

Particle therapy

Proton therapy and other charged-particle therapies use the physical property that these beams deposit most of their energy at a depth set by the beam energy and then stop, which can reduce dose to tissue beyond the target. Particle facilities are capital-intensive, so a central research question is for which patients and tumour types the dosimetric advantage translates into a meaningful clinical benefit. Comparative trials and registries are the main way this is being tested.

Brachytherapy and radiopharmaceuticals

Brachytherapy places sealed radioactive sources inside or next to the tumour, which gives a very steep dose fall-off and is established in the treatment of cervical and prostate cancers, among others. Radiopharmaceutical (targeted radionuclide) therapy instead gives a radioactive drug that seeks out tumour cells throughout the body. This second area overlaps with nuclear medicine and is one of the faster-growing parts of the field, which also brings it into contact with the imaging research described in What Is Radiology? and with the isotope handling rules discussed later on this page.

Emerging areas

Active research areas include adaptive radiotherapy (re-planning during the course of treatment as the anatomy changes), MR-guided delivery, combinations of radiation with immunotherapy, ultra-high dose-rate (“FLASH”) delivery, which is still investigational, and the use of artificial intelligence to automate contouring and planning.

Research Methods in Radiation Oncology

Four methodological traditions meet in this field.

Radiation biology studies how radiation damages DNA and how cells and tissues repair, repopulate and respond. Laboratory work uses cell lines, three-dimensional culture, and animal models to test how dose, fractionation and drug combinations change tumour and normal-tissue response. Animal studies of this kind fall under the oversight described in animal research ethics.

Medical physics and dosimetry research develops and validates the machines, measurement methods and computational models that make planning and delivery accurate. Treatment-planning data are exchanged in the DICOM standard and its radiotherapy extensions, and dose-volume data are used to build models that estimate the probability of tumour control and of normal-tissue complications.

Clinical trials test whether a change in technique, dose or combination improves outcomes. Radiation oncology trials have features that differ from drug trials: the intervention is a technical process that must be delivered consistently across sites, so protocol compliance depends on credentialing and review of the radiation plans themselves. Typical endpoints include local control, progression-free and overall survival, and rates of acute and late toxicity. Because late effects can emerge years after treatment, long follow-up is a standing feature. The general design questions are covered in What Makes Oncology Clinical Trials Different: RECIST, Endpoints, and the NCTN, and the statistical logic of margins and comparisons is explained in non-inferiority versus superiority trial design, which matters whenever a trial asks whether a shorter or less intensive radiation schedule can be as good as the standard.

Outcomes and health-services research uses registries, claims data and comparative-effectiveness methods to study access, cost, quality and disparities in radiotherapy. Much of this work depends on sound data stewardship, including the requirements in the NIH Data Management and Sharing Plan guide.

Cooperative Groups, the NCTN and NRG Oncology

Large practice-changing radiation trials are usually too big for a single institution, which is why the cooperative group model matters. In the United States, the National Cancer Institute (NCI) funds a network of academic and community sites that run multi-institution trials under shared protocols. That network is now the National Clinical Trials Network (NCTN), which NCI launched in 2014 to consolidate the earlier Cooperative Group Program.

NRG Oncology is the NCTN group with the deepest roots in radiation oncology. It was formed in 2012 through the combination of three legacy groups: the National Surgical Adjuvant Breast and Bowel Project (NSABP), the Radiation Therapy Oncology Group (RTOG) and the Gynecologic Oncology Group (GOG). Its trials span radiation, surgery and systemic therapy, with particular strength in breast, gynecologic, prostate, brain, head and neck, lung and gastrointestinal cancers. The other adult NCTN groups, including ECOG-ACRIN, SWOG and Alliance, and the pediatric Children’s Oncology Group also run trials with radiation components. A separate group of quality-assurance centres, the Imaging and Radiation Oncology Core (IROC), provides radiotherapy and imaging quality assurance for NCI trials, including facility qualification, credentialing and review of treatment data. The administrative machinery around these trials, including the central billing and regulatory support provided through the Cancer Trials Support Unit (CTSU), is a good example of how clinical research administration supports a technical specialty.

Outside the United States, comparable collaboration happens through groups such as the European Organisation for Research and Treatment of Cancer (EORTC), the Canadian Cancer Trials Group, and national networks in the United Kingdom and elsewhere, often with ESTRO (below) providing technical guidance.

How Radiation Oncology Research Is Funded

In the United States the dominant public funder is the NIH, and within it the National Cancer Institute. NCI supports radiation oncology through investigator-initiated project grants, cancer centre support, the NCTN and its quality-assurance infrastructure, and a dedicated Radiation Research Program that sets priorities for radiation biology, physics and clinical research. For how NCI mechanisms and paylines actually work, see NCI Funding and the wider cancer research funding landscape. Imaging-heavy and technology-heavy work may also fit the National Institute of Biomedical Imaging and Bioengineering (NIBIB). Early-career investigators commonly use the pathway described in K99/R00 Pathway to Independence awards, and multi-site trials often run on cooperative agreements of the kind defined in the dictionary entry for the U01 NIH cooperative agreement.

Other sources include the Department of Defense and other federal programmes for selected topics, cancer charities and foundations, professional-society research awards, industry funding for devices, software and radiopharmaceuticals, and institutional funds. In the United Kingdom, Cancer Research UK, the National Institute for Health and Care Research and the UKRI councils (see MRC funding) fund radiotherapy research. Because industry is deeply involved in machines, planning software and isotopes, conflict-of-interest management and contract structure are routine administrative concerns in radiation oncology grants. For a broader grounding in these functions, see the research administration hub.

Societies, Journals and Standards Bodies

The American Society for Radiation Oncology (ASTRO) is the field’s principal professional society in the United States. It was founded on November 18, 1958, as the American Club of Therapeutic Radiologists, later became the American Society for Therapeutic Radiologists, and in 1983 took the name American Society for Therapeutic Radiology and Oncology, from which the ASTRO acronym comes; it has since been renamed to its current form. ASTRO holds a large annual meeting, publishes clinical practice guidelines and consensus statements, and publishes journals. The American Association of Physicists in Medicine (AAPM) is the corresponding society for medical physicists, and the American College of Radiology (ACR) contributes practice parameters and accreditation programmes. In Europe, the European Society for Radiotherapy and Oncology (ESTRO) plays a parallel role, and in the United Kingdom the Royal College of Radiologists oversees training in clinical oncology.

The principal journals include the International Journal of Radiation Oncology • Biology • Physics, known as the Red Journal and ASTRO’s official scientific journal, together with Practical Radiation Oncology and Advances in Radiation Oncology from ASTRO, Radiotherapy and Oncology from ESTRO, Medical Physics from AAPM, and Radiation Research from the Radiation Research Society.

Medical Physics: The Engine Room of the Field

Medical physics is not a side topic in radiation oncology; it is built into every treatment. Clinical medical physicists commission and calibrate treatment machines, verify that each patient’s plan can be delivered as calculated, run routine quality assurance, and lead investigation when something goes wrong. Medical physics research develops new dose-calculation algorithms, motion-management methods, imaging for treatment guidance, and the dosimetry standards that let a dose measured in one centre mean the same thing in another. The unit of absorbed dose is the gray (Gy), and standardising how dose is specified and reported is a recurring technical concern in trial protocols.

In the United States, medical physics training is typically a graduate degree in medical physics or a related physical science followed by a clinical residency, and the American Board of Radiology certifies medical physicists. Many educational programmes are accredited by the Commission on Accreditation of Medical Physics Education Programs (CAMPEP). The discipline is closely tied to physics, nuclear physics and biomedical engineering.

Radiation Safety in Radiation Oncology Research

Radiation oncology research handles radiation and radioactive material in several ways, and each has a compliance layer.

• Radioactive materials. Sealed sources for brachytherapy, and unsealed radionuclides used in laboratory work or radiopharmaceutical studies, fall under licensing. In the United States, the Nuclear Regulatory Commission (NRC) regulates byproduct material, including its medical use under 10 CFR Part 35, and many states regulate on the NRC’s behalf as Agreement States. Institutions typically hold a licence overseen by a radiation safety officer; see What a Radiation Safety Officer Does and the dictionary entry for the radiation safety committee.
• Radiation-producing machines. Linear accelerators and similar devices produce radiation only when energized and are generally regulated at state level rather than as licensed material, but they carry the same shielding, access control and survey requirements.
• Worker protection. Occupational exposure is governed by dose limits and the ALARA principle (as low as reasonably achievable). The practical rules are laid out in Occupational Radiation Dose Limits Under 10 CFR 20, Time, Distance, Shielding: Applying ALARA and How Dosimetry Badges Work.
• Waste. Radioactive waste from isotope work has to be segregated and handled correctly; see Radioactive Waste Disposal in the Lab.
• Human participants. When radiation is the study intervention, the protocol must describe dose and risk to the IRB, and trials add central review of the radiation plans. When radiation is given only for research purposes, such as additional imaging, review bodies commonly examine the dose and the justification separately from routine care.

This is a summary, not a compliance manual. The licence, the state or national regulator and the institution’s own radiation safety programme determine what applies to a specific project.

A Short History

The field’s origins are in the discovery of X-rays by Wilhelm Conrad Röntgen in 1895 and of radium by Marie and Pierre Curie and their collaborators a few years later. Therapeutic use followed quickly, though early practice was empirical and hazards to patients and practitioners were not well understood. The twentieth century added standardised dose measurement, the development of megavoltage machines, and the linear accelerator; later decades brought computed-tomography-based planning, three-dimensional conformal treatment, IMRT, image guidance and stereotactic delivery.

Training and Career Pathways

In the United States, becoming a radiation oncologist requires a medical degree (MD or DO), followed by an ACGME-accredited radiation oncology residency of four years, usually taken after a preliminary or transitional clinical year, and board certification through the American Board of Radiology (ABR). Some graduates take additional fellowship or research training, and physician-scientists often pursue MD-PhD training or protected research time. Medical physicists, dosimetrists and radiation therapists follow separate education and credentialing routes. Other countries organise training differently; in the United Kingdom, for example, the equivalent specialty is called clinical oncology and covers both radiotherapy and systemic anticancer therapy.

Research careers include the clinical trialist who leads protocols within a cooperative group, the translational scientist working in radiation biology, the physicist developing new delivery and planning methods, the outcomes researcher using registry data, and the research administrators and regulatory staff who keep trials compliant. Anyone in a supporting role will find the surrounding disciplines useful, including hematology (blood cancers and total body irradiation before transplant), immunology (the basis of radiation-immunotherapy combinations), biostatistics and genomics.

Explore More Branches of Science

This guide belongs to CASRAI’s Branches of Science hub, which organizes guides to individual disciplines with the research-administration detail (funders, methods, career paths) that general encyclopedia entries leave out. Related guides include radiology, medical imaging and hematology.

Frequently Asked Questions

What is the difference between radiation oncology and radiology?

Radiology uses imaging, such as X-ray, CT, MRI, ultrasound and nuclear medicine, to diagnose disease and guide procedures. Radiation oncology uses radiation to treat cancer. The specialties share physics foundations and often work together on treatment planning, but they have separate residencies and board certification. See What Is Radiology?.

Are radiotherapy and radiation therapy the same thing?

Yes. Radiotherapy and radiation therapy are two names for the same treatment, with radiotherapy more common in British usage and radiation therapy in American usage. “Radiation oncology” names the medical specialty that prescribes and oversees it. In some countries the specialty is called clinical oncology or therapeutic radiology.

What is the difference between radiation oncology and medical oncology?

Radiation oncologists treat cancer with radiation, while medical oncologists treat it mainly with drugs such as chemotherapy, targeted therapy and immunotherapy. Many patients see both, and many clinical trials combine the two modalities.

What does NRG Oncology do?

NRG Oncology is an NCI-funded NCTN group that designs and runs multi-institution cancer clinical trials, with strong roots in radiation therapy, surgical oncology and gynecologic oncology through its legacy groups NSABP, RTOG and GOG.

Who funds radiation oncology research?

In the United States the main funder is the NIH, chiefly NCI, with NIBIB and other institutes funding related work. Foundations, professional societies, industry and, outside the US, bodies such as Cancer Research UK also contribute. See NCI Funding.

How long does it take to become a radiation oncologist in the United States?

After a bachelor’s degree, it takes four years of medical school and then a four-year ACGME-accredited residency, usually following a one-year preliminary or transitional clinical year, so about nine years of training after a bachelor’s degree. Optional fellowships add more time.

Do radiation oncology researchers need a radiation safety licence?

It depends on what they handle. Work with radioactive materials generally runs under an institutional licence and a radiation safety programme, and machine-produced radiation is governed by shielding, survey and state requirements. Your institution’s radiation safety officer determines what applies to a specific project.