Radiation Therapy

Radiation therapy (also known as radiotherapy) is a type of cancer treatment that uses high-powered energy beams—X-rays most commonly but other types of energy as well—to kill cancer cells and shrink tumors in their path while doing the least damage to the surrounding healthy tissue. Radiation therapy is used in a number of ways. How it is used depends on a patient's type and stage of lung cancer and medical and other factors:

  • as a patient's primary treatment (e.g., when a patient's health cannot tolerate surgery or if a patient chooses not to have surgery)
  • before surgery to help reduce the size of a tumor to make it easier to remove
  • after surgery to kill any remaining cancer cells
  • as a treatment for lung cancer that has spread to another area of the body, such as the brain
  • to relieve symptoms in advanced lung cancer, such as pain or shortness of breath, by shrinking the tumor1,2,3,4,5,6

Radiation therapy may potentially be used at all stages of both non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC).

How does radiation therapy work?

Radiation therapy works by damaging the cancer cells’ ability to grow and multiply; it attacks the DNA within the cells that control these functions. When the cancer cells die, the body naturally eliminates them. Unlike systemic chemotherapyTreatment with drugs that kill cancer cells, which kills cancer cells wherever they are throughout the body, radiation only kills cancer cells directly in the path of the radiation beam. Radiation therapy damages cancer cells, which divide rapidly, more than normal, healthy cells, but it does damage the normal, healthy cells in its path as well. Fortunately, these normal, healthy cells are often able to repair a large part of the damage caused by the radiation therapy. The goal in radiation therapy is to give doses of radiation that are large enough to kill as many of the cancer cells as possible but at the same time do as little damage to the normal, healthy cells in the area where the radiation is given.7,8,9

Radiation therapy does not work immediately, and it varies in its effectiveness by patient. It takes days or weeks before the damage to the DNA is enough for the cells to die. After radiation therapy ends, the cancer cells continue to die for up to months after.7,9

Radiation therapy can cause side effects. Common side effects and their management are discussed later in this section.

Who is on the radiation therapy team, and what are their roles?

A patient’s radiation therapy team includes a number of professionals. Among them are these key team members:23,24,25,26,27

  • Radiation oncologist: The radiation oncologist has overall responsibility for a patient’s radiation therapy treatment. It is the radiation oncologist who determines, based on consultation with the patient’s other doctors and other medical information, whether a patient might be a candidate for radiation therapy and what treatment might be the best. The radiation oncologist develops and prescribes the radiation therapy plan, makes sure that the treatment is given accurately, monitors the patient’s progress, and adjusts the plan as necessary to make sure it is the most effective plan possible. The radiation oncologist meets regularly with patients.
  • Radiation therapist: The radiation therapist delivers the radiation treatments, keeps records, and makes sure that the machine delivering the radiation is working properly. The radiation therapist also lets the radiation oncologist know if the patient is experiencing any problems with the treatment.
  • Medical physicist: The medical physicist is responsible for the quality control of the radiation equipment and the radiation treatment procedures. The medical physicist ensures that the equipment is working as it should by conducting safety tests regularly, including measuring the radiation beam itself. The medical physicist works closely with the dosimetrist.
  • Dosimetrist: Although it is the radiation oncologist who prescribes the radiation dose for a patient, it is the dosimetrist’s job to make the very complex and technical calculations that determine a patient’s personalized radiation treatment plan.
  • Radiation oncologist nurse: The radiation oncology nurse cares for a patient during the entire course of the radiation treatment: before, during, and after. The radiation oncology nurse is there to answer any questions, monitor a patient’s health, and help manage any side effects. 

How is radiation therapy administered?

Radiation can come from a machine outside the body (external beam radiation therapy) or from radioactive material placed inside the body (internal radiation therapy). Before any radiation treatment is decided on, the radiation oncologist may do a physical exam, take a medical history, and consider other factors.

External Beam Radiation Therapy (EBRT)

When radiation therapy is directed at the lung cancer from outside the body, it is called external beam radiation therapy (EBRT). This is the type of radiation therapy most often used to treat both non-small cell lung cancer and small cell lung cancer. The radiation machine used most often is a linear accelerator, also known as a "linac."5,6,28

Body moldSimulation

Before EBRT is started, during a planning session known as "simulation," measurements are taken to determine the proper dose of radiation and the correct angles for aiming the radiation beams. Imaging tests, such as CT scans, are used to pinpoint the precise area of the body to be treated.The patient may be fitted with a body mold that restricts movement; it also helps ensure that the patient stays immobilized and so maintains the same position for each treatment. Likewise, small dots (that can be either temporary or permanent) are put on the patient's skin; these serve as guides to make sure that the treatment area is consistent for all of the radiation sessions.3,5,6,8,9

►Timing of radiation treatments

Radiation treatments do not begin right away after the simulation. It takes time, up to a week or two, for the medical physicist and dosimetrist to make and then check all of the calculations, based on the results from the simulation, that are to be used in the precise set-up of the radiation machine for a patient. Treatments start after the radiation oncologist gives final approval.29,30

► What happens during radiation treatments?

During the treatment, radiation beams are targeted at the marked area from the machine, which is large and can be noisy. While the machine does not touch the patient's body, it may move around it. Radiation therapy is painless. Each session lasts 10-30 minutes.5,6,8,9

EBRT machine
Image credit: National Cancer Institute

A radiation therapy schedule usually consists of a specific number of treatments given over a set period of time; this varies by circumstance. For example, a course for lung cancer could consist of sessions 5 days per week (Monday-Friday) for 6 to 7 weeks, for a total of 30 to 35 treatments.5,6,8

Radiation therapy schedule

In addition to the 5 weekly radiation sessions, a patient has a weekly meeting with the radiation oncologist and oncology nurse. These are called on-treatment visits, or OTVs. At the OTV, patients can be assessed for side effects from treatment and any other concerns discussed. The OTV takes place even when a patient is feeling good. Based on the radiation oncologist's appraisal at the OTVs, a patient's treatment plan may be adjusted.31,32,33

After the radiation treatments have ended, a patient continues to see the radiation oncologist for follow-up observation and care; the radiation oncologist determines how often and for how long this will be necessary.32,33

Types of EBRT

The radiation oncologist determines which EBRT technique may be best for a patient.  These techniques include:

  • Three-dimensional conformal radiation therapy (3D-CRT): Three-dimensional conformal radiation therapy, 3D-CRT, uses imaging technology (CT, MRI, PET, or PET-CT) to generate 3D images of a patient's tumor and the surrounding area. This level of detail allows for a stronger dose of radiation to be administered to the tumor while causing less damage to the normal, healthy tissue around the tumor.5,6,10,14
  • Four-dimension conformal radiation therapy (4D-CRT): This technique goes further than 3D-CRT by also measuring and taking into account the motion that tumors might naturally make while a patient is undergoing treatment, e.g., from breathing.34

  • Intensity-modulated radiation therapy (IMRT): IMRT also uses three-dimensional imaging. Coordinates of the tumor from the imaging are used to program a machine that can then deliver, from multiple angles, precisely shaped and higher doses of radiation to the tumor and lower doses to the surrounding  normal, healthy tissue.  Because of the precision, IMRT is an especially useful technique for use when a tumor is situated near a vital structure, such as the spine. There is a version of IMRT, volumetric modulated arc therapy (VMAT), that uses a machine that requires only one rotation around the body to deliver radiation, which means that the treatment time is shorter. 5,6,11,12,13,14

  • Image-guided radiation therapy (IGRT): A specialized form of IMRT used in NSCLC, IGRT uses sophisticated imaging testsAny test that uses a form of energy, such as X-rays, ultrasounds, radio waves, or radioactive substances, to make detailed pictures of areas inside the body to verify the position of the patient and the location of the tumor both prior to and during the delivery of the treatment. This leads to less normal, healthy tissue being harmed.12,13,14

  • Stereotactic body radiation therapy (SBRT): Stereotactic body radiation therapy (SBRT), also called stereotactic ablative radiotherapy (SABR), is most often used to treat early-stage NSCLC when a patient’s health does not allow surgery or a patient does not want surgery. It can be used for tumors small in size (5 cm or less). It may also be used if an NSCLC patient has limited metastases. SBRT combines image-guided radiation therapy (IGRT) with even more advanced techniques to precisely deliver extremely high doses of radiation to the tumor while decreasing the dose to normal, healthy tissue nearby. Instead of giving small doses of radiation each day for several weeks, SBRT can be given in two to five treatments. When the treatment is delivered in only one session, it is referred to as stereotactic radiosurgery (SRS).3,5,16,17

  • Proton therapy: Proton therapy is a type of radiation therapy that uses protons instead of X-rays to treat cancer. Like X-rays, the proton beam damages the DNA within the cancer cells, leading to the cells' death. As with the other radiation therapy techniques, imaging is done to determine where exactly the radiation needs to go. The machine used, known as a cyclotron or synchotron, propels the protons at high speed. The main advantage of proton therapy is that all of the radiation is released when it gets to the tumor, so radiation damage to the normal, healthy tissue in the area is lessened; this may allow a higher radiation dose to be given to the tumor. However, proton therapy is very expensive and is not covered by all insurance companies for all diagnoses. In addition, it requires expensive and specialized equipment that only a handful of hospitals in the United States have.18,19

Internal Radiation Therapy

Radiation sources can be placed inside the body in solids or in liquids. Most often, they are placed in the form of solids. This type of internal radiation therapy is  brachytherapy.  During treatment, a small source of radioactive material, often in the form of small pellets or seeds, is inserted directly into the cancer or into the airway next to the cancer. This is usually done during bronchoscopyA procedure that uses a thin, tube-like instrument with a light and a lens to examine the inside of the trachea, bronchi, and lungs or during surgery. The radiation travels only a short distance from the implanted radiation source to the tumor, which limits damaging effects on surrounding normal, healthy tissue. The radioactive material may be removed after a short time—several minutes for high-dose-rate brachytherapy or up to a few days for low-dose-rate brachytherapy. Alternately, the “seeds” are left in place permanently, and the radiation gets weaker over time until it is all absorbed.5,7,9

Brachytherapy seeding

When is radiation therapy administered in non-small cell lung cancer (NSCLC) treatment?

The type of radiation therapy most often used to treat NSCLC is external beam radiation therapy (EBRT). In patients with early-stage NSCLC, in which there is only a single small nodule in the lung without any spread to nearby lymph nodes, stereotactic body radiation therapy (SBRT) is typically given. SBRT is recommended for patients who cannot be treated surgically.3

In more advanced stages of NSCLC, EBRT may be given alone or along with chemotherapy as the main treatment. It is also used after surgery, alone or along with chemotherapy, to try to kill any small deposits of cancer that surgery may have missed. EBRT may be used prior to surgery, as neoadjuvant therapyTreatment given prior to the main treatment in order to shrink a tumor, typically along with chemotherapy, to try to shrink a lung tumor to make it easier to operate on. Internal radiation therapy and EBRT are also used as palliative care to shrink tumors to relieve symptoms of advanced lung cancer, such as bleeding, trouble swallowing, cough, and shortness of breath.3

When is radiation therapy administered in small cell lung cancer (SCLC) treatment?

The type of radiation therapy most often used to treat SCLC is EBRT. Most often, radiation therapy administered as the initial treatment for small cell lung cancer is given once or twice daily, 5 days a week, for 3 to 7 weeks.6

Radiation therapy schedule

EBRT is most often given at the same time as chemotherapy in limited-stageCancer that is in the lung where it started and may have spread to the area between the lungs or to the lymph nodes above the collarbone disease to treat the tumor and lymph nodes in the chest. Sometimes it is given after chemotherapy, as adjuvantCancer treatment given after the primary treatment in order to kill unseen cancer cells or to lower the risk that the cancer will come back therapy, to try to kill any small areas of cancer that may remain.4,6

In extensive-stage small cell lung cancer (SCLC)Cancer that has spread widely throughout a lung, to the other lung, to lymph nodes on the other side of the chest, or to distant organs, EBRT may be used to shrink tumors to relieve symptoms of lung cancer such as bleeding, trouble swallowing, cough, and shortness of breath.4,6

Since the brain is a common place for metastasis in SCLC, radiation may be given to the brain after other treatments to help lower the chances that the cancer will spread there. This type of radiation is called prophylactic cranial irradiation.4,6

Radiation to relieve symptoms and prophylactic cranial radiation are given for shorter periods, usually less than 3 weeks.4,6

Managing common side effects of radiation therapy

Side effects from radiation therapy are caused by the damage to the normal, healthy cells that are near the cancer cells that are being treated. One major advantage of the more precise radiation therapy techniques that have been developed is that fewer of the normal, healthy cells are damaged so that the side effects are lessened.20

Side effects from radiation therapy for lung cancer are common, but just because a side effect is common does not mean that a patient will experience it. Before treatment begins, a patient should discuss with the radiation healthcare team what side effects might be expected and how to prevent or ease them. A patient should speak with the radiation healthcare team if and when new side effects begin, as treating them early on is often more effective than trying to treat them once they have already become severe. (The OTV is a handy time to have this discussion.) Although most radiation therapy side effects go away when treatment is over, some can last a long time or even be permanent.

The side effects and management techniques listed below are not all-inclusive. The radiation healthcare team will have a more comprehensive list of side effects and can offer a patient a personalized set of recommendations for their management.

Common side effects of radiation therapy and ways to manage them:2,5,9,20,21

  • Fatigue: Fatigue can be treated with plenty of sleep, rest betwen activities, exercise, relaxation techniques (e.g., medication or yoga), good nutrition, and treatments (if appropriate) for anemia or depression.
  • Sunburn-like skin changes, such as dryness, itching, or peeling: Symptoms may be relieved by washing with gentle soap and warm water (not hot) and using unscented creams/lotions.
  • Hair loss: Hair will only fall out in the area where the radiation enters the body. (If radiation therapy is only to the chest area, for example, there will be no loss of hair on the head.)
  • Cough, difficulty breathing, and shortness of breath: These symptoms can develop as “radiation pneumonitis” up to months after therapy and may require anti-inflammatory medication.
  • Sore throat and trouble swallowing: Pain and anti-inflammatory medications and speech pathology to learn different ways to swallow may help.
  • Loss of appetite and weight loss: Appetite stimulants and nutritional supplements may be given to improve appetite and reduce weight loss.
  • Nausea and vomiting when the treated area is near the stomach: Bland and easy-to-digest foods and frequent small meals and snacks may help prevent nausea. Techniques such as distraction, relaxation, and positive imagery can help change the expectation and fear of nausea and vomiting. In addition, there are multiple medications available to prevent and treat nausea and vomiting. If one anti-nausea medication does not work, a different one or an additional one can be prescribed.

What’s new in lung cancer radiation therapy research?

There are currently clinical trialsA type of research study that tests how well new medical approaches work in people under way that aim to further improve the precision of imaging and radiation delivery techniques. Researchers are looking into new imaging techniques, and radiation therapy is also being studied in combination with surgery, chemotherapy, immunotherapy, and targeted therapyA type of treatment that uses drugs to identify and attack specific types of cancer cells with less harm to normal cells.22

If you are considering participating in a clinical trial, start by asking your doctor whether there is one for which you might qualify in your area. In addition, here are several resources to help you find one that may be a good match for you:

Learn more about clinical trials here.

Questions to ask your healthcare team about radiation therapy

Print this list

  1. What kind of radiation therapy will I get?
  2. How can radiation therapy help?
  3. How many weeks will my course of radiation therapy last?
  4. What kinds of side effects should I expect during my course of radiation therapy?
  5. Will these side effects go away after radiation therapy is over?
  6. What kind of late side effects should I expect after radiation therapy is over?
  7. What can I do to manage these side effects?
  8. What will you do to manage these side effects?
  9. How can I learn more about radiation therapy?

Updated August 6, 2019


  1. Lung Cancer — Non-Small Cell:Types of Treatment. Cancer.Net website. https://www.cancer.net/cancer-types/lung-cancer-non-small-cell-types-treatment. Approved January 2019. Accessed June 25, 2019.
  2. Lung Cancer Treatment. RadiologyInfo.org. https://www.radiologyinfo.org/en/info.cfm?pg=lung-cancer-therapy#therapy-treatment. Reviewed July 16, 2018. Accessed June 25, 2019.
  3. Non-Small Cell Lung Cancer. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®). Version 4.2019. https://www.nccn.org/professionals/physicians_gls/pdf/nscl.pdf. Posted April 29, 2019. Accessed June 25, 2019.
  4. Small Cell Lung Cancer. NCCN Clinical Practice Guidelines in Oncology (NCCN Guidelines®). Version 1.2019. https://www.nccn.org/professionals/physician_gls/pdf/nscl.pdf. Posted April 9, 2019. Accessed June 25, 2019.
  5. Radiation Therapy for Non-Small Cell Lung Cancer. American Cancer Society website. https://www.cancer.org/cancer/non-small-cell-lung-cancer/treating/radiation-therapy.html. Revised May 16, 2016. Accessed June 25, 2019.
  6. Radiation Therapy for Small Cell Lung Cancer. American Cancer Society website. https://www.cancer.org/cancer/small-cell-lung-cancer/reating/radiation-therapy.html. Revised May 16, 2016. Accessed June 25, 2019.
  7. Radiation Therapy to Treat Cancer. National Cancer Institute website. https://www.cancer.gov/about-cancer/treatment/types/radiation-therapy. Revised January 8, 2019. Accessed June 25, 2019.
  8. Radiation therapy. Mayo Clinic website. https://www.mayoclinic.org/tests-procedures/radiation-therapy/about/pac-20385162. Updated March 28, 2018. Accessed June 25, 2019.
  9. Radiation Therapy and You: Support for People with Cancer. National Cancer Institute website. https://www.cancer.ogv/publications/patient-education/radiationtherapy.pdf. Accessed June 25, 2019.
  10. 3D CRT (Three-Dimensional Conformal Radiation  Therapy). Moffitt Cancer Center website. https://moffitt.org/treatments/radiation-therapy/3d-crt-three-dimensional-conformal-radiation-therapy/. Accessed June 25, 2019.
  11. IMRT (Intensity Modulated Radiation Thearpy). Moffit Cancer Center website. https://moffitt.org/treatments/radiation-therapy/imrt-intensity-modulated-radiation-therapy/. Accessed June 25, 2019.
  12. Image-guided Radiation Therapy (IGRT). RadiologyInfo.org website. https://www.radiololgyinfo.org/en/info.cfm?pg=igrt. Reviewed April 3, 2018. Accessed December 10, 2019.
  13. IMRT. UCLA Health website. https:/www.uclahealth.org/radonc/imrt-igrt. Accessed June 25, 2019.
  14. Hegi F, Atwood T, et al. Chapter 34: Technical Requirements for Lung Cancer Radiotherapy. In: Pass HI, Ball D, Scagliotti GV, eds. IASLC Thoracic Oncology, Second Edition. Philadelphia, PA: Elsevier; 2018. 318-329. Accessed June 25, 2019.
  15. FAQs: Stereotactic Body Radiation Therapy (SBRT); UCLA Health website. https://www.uclahealth.org/radonc/faqs-sbrt. Accessed June 26, 2019.
  16. SBRT (Stereotactic Body Radiation Therapy). Moffitt Cancer Center website. https://moffitt.org/treatments/radiation-therapy/sbrt-stereotactic-body-radiation-therapy/.  Accessed June 26, 2019.
  17. Non-Small Cell Lung Cancer Treatment (PDQ®)—Patient Version. National Cancer Institutewebsite. https://www.cancer.gov/types/lung/patient/non-small-cell-lung-treatment-pdq. Updated May 31, 2019. Accessed June 26, 2019.
  18. Proton Therapy. Cancer.Net website. https://www.cancer.net/navigating-cancer-care/how-cancer-treated/radiation-therapy/proton-therapy. Approved August 2018.  Accessed June 26, 2019.
  19. Stallard J. Proton Therapy: A Better Way to Destroy Tumors. Memorial Sloan Kettering Cancer Center website. https://www.mskcc.org/blog/proton-therapy-better-way-destroy-tumors. Posted February 17, 2015. Accessed June 26, 2019.
  20. Side Effects of Radiation Therapy. Cancer.Net website. https://www.cancer.net/navigating-cancer-care/how-cancer-treated/radiation-therapy/side-effects-radiation-therapy. Approved December 2018. Accessed June 26, 2019.
  21. Radiation Therapy Side Effects. National Cancer Institute website. https://www.cancer.gov/about-cancer/treatment/types/radiation-therapy/side-effects. Posted May 1, 2018. Accessed June 26, 2019.
  22. Clinicaltrials.gov. US National Institutes of Health website. http://clinicaltrials.gov. Accessed June 26, 2019.
  23. What to /Expect When Having Radiation Therapy. Cancer.Net website. https://www.cancer.net/navigating-cancer-care/how-cancer-treated/radiation-therapy/what-expect-when-having-radiation-theapy. Approved December 2018. Accessed August 6, 2019.
  24. Radiation Oncology Team. Targeting Cancer website. https://www.targetingancer.com.au/radiation-oncology-team/. Accessed August 6, 2019.
  25. Professions in Radiation Therapy. RadiologyInfo.org website. https://www.radiologyinfo.org/en/info.cfm?pg=professions-radiation-therapy. Copyright 2019. Accessed August 6, 2019.
  26. What is a Medical Dosimetrist? American Association of Medical Dosimetrists website. https://www.medicaldosimetry.org/about/medical-dosimetrist/. Accessed August 6, 2019.
  27. Radiation Oncology Treatment Team. UCLA Department of Radiation Oncology website. https://www.uclahealth.org/radonc/radiation-oncology-treatment-team. Accessed August 6, 2019.
  28. Understanding Radiation Therapy. Cancer.Net website. https://www.cancer.net/navigating-cancer-care/how-cancer-treated/radiation-therapy/understanding-radiation-therapy. Approved May 2018. Accessed August 6, 2019.
  29. Radiation Therapy Simulation: What to Expect. Sibley Memorial Hospital website. https://www.hopkinsmedicine.org/sibley-memorial-hospital/patient-care/specialty/cancer/treatments/radiation-oncology/radiation-therapy-simulation.html. Accessed August 6, 2019.
  30. Step-by-Step Through Treatment. UC Davis website. https://health.ucdavis.edu/radonc/patients/Rx_stepbystep.html. Copyright 2019. Accessed August 6, 2019.
  31. FAQs: What is Radiation Therapy? Beth Israeel Deaconess Medical Center website. https://www.bidmc.org/centers-and-departments/radiation-oncology-faqs .Copyright 2018. Accessed August 6, 2019.
  32. Pictorial Overview of the Radiation Therapy Treatment Process. OncoLink website. https://www.oncolink.org/cancer-treatment/radiation/introduction-to-radiation-therapy/pictorial-overview-of-the-radiation-therapy-process. Reviewed July 5, 2018. Accessed August 6, 2019.
  33. About Your Treatment. Washington University School of Medicine in St. Louis Department of Radiation Oncology website. https://radonc.wustl.edu/patient-care/about-your-treatment. Copyright 2019. Accessed August 6, 2019.
  34. 3D & 4D Conformal Radiation Therapy and Intensity Modulated Radiation Therapy (IMRT). The Angeles Clinic and Research Institute website. http://www.theangelesclinic.org/Home/PatientEdcarionLibrary/tabid/19283/ctl/View/mid/35200/Default.aspx?ContentPubID=419. Copyright 2019. Accessed August 6, 2019.