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32

NCCN Guidelines for Patients

®

:

Colon Cancer, Version 1.2017

Radiation therapy

Radiation therapy uses high-energy, highly focused

rays to treat cancer. The rays damage DNA. This

either kills the cancer cells or stops new cancer cells

from being made.

Radiation therapy is not often used to treat colon

cancer. You may receive radiation therapy as part of

a clinical trial. Otherwise, Parts 4 and 5 explain when

radiation therapy is an option.

External radiation

Most often, EBRT (

e

xternal

b

eam

r

adiation

t

herapy) is the method used to treat colon cancer.

This method delivers radiation from outside your

body using a large machine.

See Figure 13

.

The radiation passes through your skin and other

tissue to reach the tumor.

A planning session is needed to receive the best

treatment. This session is called simulation. First, you

will be guided and adjusted into the position needed

for treatment. After this, pictures of the cancer sites

will be made with an imaging test.

Using the pictures, your radiation team will plan

treatment. A team consists of doctors, medical

physicists, and technical experts in radiation

planning. They will plan the best dose, number and

shape of radiation beams, and number of treatments.

Conformal techniques are used for colon cancer.

These techniques shape the radiation dose to the

cancer site to spare healthy tissue. However, some

healthy tissue still gets radiated. The radiation dose

is shaped with computer software and hardware

added to the machine. The types of conformal

radiation include:

†

†

3D-CRT (

three

-

d

imensional

c

onformal

r

adiation

t

herapy) delivers, from different

angles, a photon beam that matches the shape

of the tumor. Treatment is completed in about 6

weeks.

†

†

IMRT (

i

ntensity-

m

odulated

r

adiation

t

herapy)

is a form of 3D-CRT that further modifies the

beam’s intensity during treatment. Treatment is

completed in about 6 weeks. IMRT should be

used only for a second treatment with radiation

or for cancer in an uncommon site.

†

†

SBRT (

s

tereotactic

b

ody

r

adiation

t

herapy)

treats cancer with very precise, high-dose

photon beams. Receiving SBRT is much like

other conformal techniques except treatment

is finished in about 5 visits. At this time, SBRT

should only be used to treat colon cancer in the

liver or lungs.

3

Overview of cancer treatments

Radiation therapy

Figure 13

External beam radiation therapy

Radiation therapy is often delivered from a

large machine. The rays pass through skin and

travel to the tumor. Healthy tissue is protected

using modern types of treatment.