3D CRT is a type of external beam radiation therapy, which involves the delivery of the radiation beams from a source outside the body to eradicate the cancer cells.
This technique is usually used in cases of tumors too close to the vital organs.
The different types of cancers that may be treated using 3D CRT include:

• Lung cancer
• Liver cancer 
• Brain cancer
• Prostate cancer
• Head and neck cancer

The following diagnostic tests are recommended before a 3D CRT procedure:

1. Physical examination: The patient’s symptoms, medical history, and overall physical health are assessed by the doctor.
2. Blood tests: Certain medical conditions can be detected with the help of blood tests.
3. Imaging tests: The three-dimensional image of the tumor is obtained following with the help of the following different types of imaging tests:
4. CT (computed tomography) scan: A combination of x-rays and computer technology are used to create pictures of the tumor.
5. MRI (magnetic resonance imaging) scan: Strong magnetic fields and radio waves to create detailed images of the tumor.
6. PET (positron emission tomography) scan: The biochemical or metabolic function of the tissues and organs can be assessed using this type of imaging test.
7. PET-CT scan: Two imaging techniques, which are the PET scan and the CT scan, are merged in this technique and each one of the above imaging tests records a different body part.
8. Endoscopy: An endoscope (a tube with a camera on one end) is used by the doctor for internally examining an organ.
9. Biopsy: The suspected tissue growth is surgically excised and sent to the laboratory for evaluation under the microscope to check for the presence of cancer cells and the type of cancer cells that may be present.

The doctor will set up the radiation therapy session according to the three-dimensional images of the tumor obtained, as well as the information from the simulation procedure.
You will be told to lie on the custom-fit mold, mask, or cast on the x-ray table.
A machine called a linear accelerator is then used to deliver the radiation beams.
The linear accelerator will move in a circular manner around the tumor region.
Radiation beams will be emitted from several directions to match the exact height, width, and depth of the tumor.
The actual radiation beam emission session lasts only for a few minutes.
However, the total time taken to complete a radiation therapy session may be approximately half an hour, which includes the preparation time needed for the radiation therapy session 
The doctor decides the treatment schedule of the patient, including how many times a week the radiation therapy session needs to be repeated in a particular patient. This may vary depending on the type of tumor being treated and the overall health status of the patient.

3D CRT may be associated with the following complications:

• Sore throat
• Changes in taste
• Loss of appetite
• Hair loss at the treatment site
• Tenderness at the treatment site
• Heartburn
• Difficulty in swallowing
• Nausea
• Vomiting
• Fatigue
• Lung problems
• Esophagitis (food pipe inflammation)