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NCCN Guidelines for Patients



Rectal Cancer, Version 1.2017


Treatment planning

Imaging tests

Some imaging tests use contrast. Contrast is a dye

that will be injected into your bloodstream. It makes

the pictures clearer. Some people have an allergic

reaction to the dye. Tell your doctor if you’ve had

problems with contrast in the past.

CT with contrast

CT (




omography) takes many pictures of

a body part using x-rays. A computer combines the

x-rays to make one detailed picture. The picture is

saved for later viewing by the radiologist.

CT is advised to see if the cancer has spread. Get

scans of your chest, abdomen, and pelvis. Contrast

should be used. The radiologist will look for cancer in

nearby and distant sites.

During the scan, you will need to lie face up on a

table. The table will move through the machine. As

the machine takes pictures, you may hear buzzing,

clicking, or whirring sounds.

You will be alone in the room during the test. In

a nearby room, the technician will operate the

machine. He or she will be able to see, hear, and

speak with you at all times. One scan is completed in

about 30 seconds. You will likely be able to resume

your activities right away unless you took a sedative.








maging) uses a magnetic

field and radio waves to make pictures. There are

three reasons why you may receive an MRI. Your

doctor may order an MRI if the CT scan was unclear.

Contrast should be used. Second, MRI and chest

CT without contrast may be done if you can’t receive

CT contrast. Third, you may receive a pelvic MRI to

assess the extent of the cancer in your pelvis. The

scan can show the tumor depth and if cancer is in

lymph nodes.

Getting MRI is much like getting CT. Except, you will

lie on top of and wear a coil device. The latter coil will

cover your body from below your chest to the top of

your legs. Coils will send and receive radio waves.

Straps may be used to help you stay in place. MRI

may cause your body to feel a bit warm.

Endorectal ultrasound

Instead of pelvic MRI, you may receive an endorectal

ultrasound. This test can also show the extent of

cancer in your pelvis. A small probe will be inserted

into your rectum. The probe will emit sound waves

that will bounce off of tissue and make echoes. The

echoes will make a picture that will be seen by your

doctor on a screen.


Sometimes CT is combined with PET (






omography). When used together, they

are called a PET/CT scan. PET/CT scan is not often

used to plan treatment for rectal cancer.

There are three reasons why you may have a PET/

CT scan. PET/CT can show how big a tumor is if you

have metastases. PET/CT can also find metastases

other than in the liver that would exclude surgery.

Last, PET/CT may be received if the CT scan is

unclear or you can’t receive contrast.

PET/CT may be done with one or two machines

depending on the cancer center. For PET, a sugar

radiotracer will first be injected into your body. The

radiotracer will be detected with a special camera

during the scan. Cancer cells will appear brighter

than normal cells because they use sugar more

quickly. PET can show even small amounts of