Along with chemotherapy and surgery, radiation therapy is one of the main treatments for many cancers. Here are some things you should know about this therapy, how it works, and its side effects.

2. What is radiation therapy?
• There are two main approaches to radiation therapy:
— external-beam radiation therapy, during which a machine called
a linear accelerator delivers radiation to the cancer site through
multiple beams
— internal radiation therapy, or brachytherapy, where tiny pellets
of radioactive material are placed directly inside the body near
cancer cells
• Radiation cannot be felt, seen, heard, or otherwise
perceived during treatment

3. Radiation creates small breaks within
the DNA of cancer cells, preventing the
cells from growing and dividing, and
often causing them to die.

4. External-beam radiation is given using a linear accelerator
(linac)
source of radiation
robotic table

5. Radiation oncologists aim beams using “tattoos” on patients
Source: xkcd.com/933

6. Radiation oncologists use regular imaging scans to assure
treatment accuracy and precision
X-rays for daily
verification of
positioning CT for weekly
Confirmation of
target localization

7. Positioning
X-rays
CT:
Plan
CT:
Week 5
Example scans in lung cancer

8. When patients receive radiation,
surrounding organs are often at risk for
unnecessary treatment, which can cause
side effects.

9. In lung cancer, for example, radiation may reach the
healthy lung, esophagus, or spinal cord.
right
lung
left
lung
esophagus
spinal cord

10. The challenge:
unavoidable
overlap of
target volume
and esophagus

11. Radiation beams come from various angles and at
varying intensities to target the tumor and avoid as
many other organs as possible.

12. For lung cancer, side effects caused by radiation
reaching other organs may include
skin reddening
very rare risk of
spinal cord injury
pain with swallowing
lung
inflammation

13. A course of radiation lasts
anywhere from a single treatment
for symptom relief, up to seven
weeks of daily treatment.

14. Dividing radiation into multiple
sessions of lower doses, in a practice
called fractionation, spares more
healthy issues, but in the long run
may decrease survival.

15. Many patients wonder…
Am I radioactive after treatment? Is it safe to be
around young children?
“Radioactivity” lasts about 0.000000000000000001 seconds
after treatment, so you are perfectly safe

16. Can you tell if the tumor is shrinking?
— Daily X-rays and/or weekly CT scans are mostly to
verify positioning and tumor targeting
— Tumors continue to shrink for weeks after the final treatment
— Radiation oncologists typically perform scans about two months
after completion of therapy to assess the tumor’s size

17. Will you be repeating the treatment?
— Unlike chemotherapy, radiation oncologists typically administer
a single course of treatment
— If needed, additional treatment can be given on a case-by-case
basis after weighing the benefits and risks with your care team

18. Is all this radiation, including X-rays and
CT scans, safe?
— The rate of secondary cancers due to radiation is less than 1 in
100, and likely closer to 1 in 1000
— Side effects depend on the area of the body that is treated;
treatment will only be given if the benefits will likely outweigh
the risks and the risks are acceptable to both the patient
and provider

19. Resources
Dana/Farber/Brigham and Women’s Department of
Radiation Oncology
American Society for Radiation Oncology
How Long Does Radiation Stay in Your Body After Treatment?