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Frequently Asked Questions About Radiation Therapy

COVID-19 update: We know that our patients and their families have questions related to care during this time. Please see COVID-19 Information and FAQs for Patients With Cancer for the latest updates.

Radiation therapy—sometimes called radiotherapy, X-ray therapy or irradiation—uses high doses of radiation energy to destroy or damage cancer cells. Radiation damages the DNA inside cancer cells, preventing them from dividing and spreading. Although surrounding normal cells may be affected by radiation, most of them recover and resume their regular functions. Unlike infusion therapy, which exposes the entire body to cancer-fighting drugs, radiation therapy is a localized, targeted treatment. Radiation therapy is a common treatment modality for many types of cancer. 

For more information on radiation therapy approaches used at UC San Diego Health, see Types of Radiation Therapy.


Is radiation therapy painful?

Not usually, but if you feel uncomfortable during the procedure, tell the radiation therapist.

What are the side effects of radiation therapy?

  • Nausea, diarrhea
  • Red, itching and peeling skin in the treatment area
  • Fatigue
  • Loss of appetite
  • Hair loss at the treatment site

Side effects often go away over time. If they do not, your doctor may recommend a break or change in your treatment.

Will radiation therapy make me radioactive?

External radiation therapy will not make you radioactive. If you are having internal radiation therapy, even though the radiation is contained at the tumor site, the seeds are radioactive and will emit therapeutic levels of radiation for a period of time. The radiation in seeds implanted to treat prostate cancer, for example, typically lasts for 60 days. If you are having prostate brachytherapy, your doctor may advise you to stay away from pregnant women and children and to wear a condom if you are sexually active.

Who gives radiation therapy?

Although the radiation therapist is the person who gives the radiation treatment, a team of other professionals will be involved in your radiation therapy.

  • Radiation oncologist: The doctor who specializes in using radiation to treat cancer and develops a radiation treatment plan
  • Dosimetrist: Assists the radiation oncologist with the treatment plan and determines dosage
  • Radiation physicist: Works the equipment to ensure that the right amount of radiation goes to the targeted spot
  • Radiation therapy nurse: Specializes in cancer treatment and provides information about radiation treatment and side effects

What is treatment simulation?

If you are having external radiation, you will go through a process called simulation to determine exactly where to aim the radiation. The simulation takes one to three hours. The radiation therapist will position you on the table and take X-rays, CT scans and other images to confirm the treatment area, called the port or field. Once the images are approved, the radiation therapist will mark reference points on your skin with a permanent marker. Body molds and shields are often made to keep you from moving and to protect parts of your body.

Appointments & Referrals

Radiation Oncology Locations

La Jolla


Chula Vista

4S Ranch

  • 6918 Dove Canyon Rd, Suite 103
    San Diego, CA 92127

El Centro

  • Imperial Valley Radiation Oncology
    1410 S La Brucherie Rd, Suite B
    El Centro, CA 92243

Sorrento Valley

  • California Protons Cancer Therapy Center
    9730 Summers Ridge Road
    San Diego, CA 92121

Patient Guide

Radiation Oncology Patient Handbook 

Radiation Oncology Patient Handbook Spanish 

Patient Education