General Treatment: An Overview of the Radiation Therapy Treatment Process

The following information is provided in order to aid you in understanding the Radiation Therapy process as well as what to expect during that process. These may differ slightly depending of the protocol set in place for our specific treatment option. We hope you find this information useful and welcome any suggestions to improve it. We look forward to providing you with outstanding care at the Cancer Center of Irvine.

Treatment Planning

Complex Simulation:

Before radiation treatments begin, you will be scheduled for a treatment planning process called "CT simulation". This process is where your radiation treatment team will precisely identify the area on your body where you will receive radiation. Positioning is extremely important in radiation therapy and your body will be positioned carefully in order to get the best radiation treatment. You will be in the same position during every treatment, and you will need to remain still during the treatments. A CT scan of the region to be treated is done. The entire simulation takes approximately an hour, though the actual time may vary. Since you will be lying on a hard table under the simulator for most of this time, you may experience some pain or discomfort. Should this occur, tell the radiation therapist or imaging technologists. Keep in mind that the time necessary to deliver the actual radiation therapy treatments is only minutes, not nearly as long as the time required for the simulation. In certain cases, an MRI or a PET/CT scan will also be done the same day as the CT simulation.

During the simulation visit, it might be necessary to put marks on your skin to outline the treatment field(s). These marks are in the form of very small tattoos, the size of a pinpoint or freckle, made using tattoo ink. The process of tattooing causes some temporary discomfort. Generally, between 2 and 8 tattoo marks are made, but sometimes more or less are necessary. In some treatment plans, a second set of tattoos may be necessary. While the tattoos are permanent, because of their very small size, they are not very noticeable. The tattoos are necessary to make it possible for you to bathe or shower on a daily basis without worrying about removing these important marks that show where the radiation treatments are to be delivered. Also, if any additional radiation therapy is needed in the future, the tattoos serve as a permanent record of previous treatments. In very rare instances, tattoos will not be used.

CT and 3D Holographic Reconstruction:

After simulation, details from the procedure are forwarded to medical radiation dosimetrists and medical physicists. These professionals perform highly technical calculations that will be used to set the treatment machine (linear accelerator). The dosimetrist and physicist work closely with Dr. Tokita to develop the treatment plan, a process that can take up to a week or more.

3-D Computer Treatment Physics Plan:

The treatment plan will be generated with the use of 3-D Holographic Reconstruction. These special treatment-planning computers are designed to display the radiation fields prescribed by Dr. Tokita and illustrate the radiation distribution. From this, the physicist can advise Dr. Tokita on ways to improve on the treatment. A final and completed plan will then be generated.

Start of Treatment


The actual treatments will be delivered on a Linear Accelerator. The Linear Accelerator at the Cancer Center is a dual high-energy machine capable of delivering two x-ray energy beams and five electron energy beams and is built by Varian Medical Systems.

The energy to be used and the set-up will be as outlined in the computer treatment plan and approved by Dr. Tokita.

The linear accelerator delivers high energy x-rays to parts of the body as outlined by Dr. Tokita. The x-rays are meant to injure all of the tissue exposed. By delivering sublethal doses of radiation, normal tissue will heal almost completely within 9-12 hours while tumors take 72 or more hours to heal the same injury. Using this differential, you will be treated daily. The cancer cells will begin to die from the accumulated radiation injury and the normal cells will continually heal themselves.

This machine may seem large and imposing, but think of it as your "friend". Without it, your chance to do well with this cancer may be limited. It has the wonderful ability to vastly extend the surgeon's treatment area. Most of its size is needed to shield areas of your body that do not need treatment and to cool the machine. To that end, the room must also be kept relatively cool.


Several days after the simulation and after all calculations have been performed, your treatment can begin.

The treatment machine is called a linear accelerator. You will be placed on the treatment table in the same position as you were on the CT simulator. Proper positioning usually takes 5 to 15 minutes. Once in place on the treatment table, varying degrees of imaging techniques will be used (i.e. CBCT, port films). These images will be matched with the simulation films to ensure that the treatment is going to be delivered the same way as it was simulated. Once the films and positioning are confirmed, a treatment will be delivered. While it seems like a lot of time to plan and set up, it is critical that the treatment be given as it was planned to avoid unnecessary toxicity to healthy tissue and to get the correct amount of radiation to the treatment area.

The actual administration of the radiation treatment typically takes about 5 to 15 minutes. Factors that affect the total length of the treatment include the complexity of your treatment, the particular machine on which you are being treated and how quickly you can be positioned properly for treatment.

Treatment Devices

Blocks and Shields:

A series of customized lead blocks or shields will be used to protect areas that Dr. Tokita does not want to treat. For example, if the tumor is in the breast, blocks may be used to protect the lung, heart, etc. If a tumor is in the pelvis, blocks may be used to protect the small intestines (bowel).


Other devices such as "wedges" (triangular brass or steel modifiers) can be used to further modify the radiation beam by compensating for differences in tissue thicknesses.


Occasionally, areas of tumor just under the skin can be spared from the tumor killing effects due to the power of the beam. To overcome this problem, a tissue equivalent material called "bolus" can be used to "fool" the beam. The "bolus" is placed directly on the skin and feels like a gel pad. The radiation beam will think the bolus is normal tissue and bring the radiation to the skin surface.

Molds or Casts:

Often, the patient requires very careful immobilization due to sensitive structures that are located very close to the tumor treatment site. Depending on the site of the tumor these devices will vary.

Treatment Management

Radiation Treatment Management:

Dr. Tokita is responsible for your management. He will be reviewing your treatment constantly.

Weekly Checks:

Whenever needed, Dr. Tokita or one of the nurses will meet with you for a weekly review. If you need help or have questions, do not hesitate to ask the therapists. If they do not know the answer, they will get the answer from Dr. Tokita or have you see him.

Chart Rounds:

Weekly, the department reviews each treatment chart in great detail. This is the essence of Quality Control.

Treatment Side Effects

The treatment effects will vary greatly depending on the area treated and the size of the fields needed to treat the cancer. Dr. Tokita will go over much of this information with you. Please do not hesitate to ask him any questions.

Side effects occurring during treatment are classified as "acute," while side effects after the course of your whole treatment are called "chronic". The risks involved vary a great deal depending on the area treated.


Once treatment is complete, front desk administration will help you set up your follow-up appointments. Dr. Tokita will follow you for as long as necessary to get you over the acute radiation effects.

Dr. Tokita will then get you back to your own physician for your follow-up with him or her. You or your physician may wish for Dr. Tokita to follow you, as well.

Types of Radiation

Radiation Treatment can come in several forms:

  • External Beam Radiation (EBRT):

    This treatment is delivered with the Cancer Center's Linear Accelerator and is manufactured by Varian Medical Systems.

    • X-rays:

      It is capable of delivering radiation in two x-ray modes: 6 MV and 18 MV. The 6 MVs are used for treatment of smaller body parts, i.e. head and neck, breast, arms, legs, etc., while the 18 MVs are for the chest and abdomen.

    • Electrons:

      The Linear Accelerator has the capability of delivering five electron beams: 6, 9, 12, 16 and 20 MeVs. These are used to treat skin cancers, superficial tumors just under the skin and shallow cancers anywhere in the body.

      When delivering external beam radiation (EBRT), the beam must enter and exit the body through normal tissue. By utilizing multiple entrance "ports" or "fields," we can minimize the exposure of any single area and concentrate (converge the beams) on the tumor area. This planning of treatment is a critical aspect of your therapy and requires the direct supervision of Dr. Tokita to simulate the treatment and 3-D plan with the CT scanner and treatment-planning computer.

  • Brachytherapy:

    This modality uses our ability to insert radioactive materials into different parts of the body. The obvious advantage lies in the high dose of radiation that can be delivered directly to the tumor while protecting surrounding normal tissues.

    Several treatment modalities may be used. They are as follows:

    • Iridium-192: is used at the Cancer Center in an instrument called High-Dose-Rate Remote Afterloader. The Cancer Center of Irvine is the only center in Orange County with this equipment. It has many uses:
      • Prostate Cancer: It is now being used as a Temporary Prostate Implant, as described in an article By Andy Grove (former Chairman of Intel Corp.) who was successfully treated with this modality for cancer of the prostate.
      • Breast Cancer: Using the new Mammosite breast localized radiation instrument or the multiple catheter breast implant.
      • Esophagus and Lung Cancer
      • Bile Duct and Liver Cancer
      • Bladder
    • Radiopharmaceutical Solutions
      • Yttrium-90 for liver cancer and shortly for lymphoma
      • I-131 for Hodgkin's Disease and Lymphoma
      • Quadramet for bone metastases
      • Zevalin for Non-Hodgkin's Lymphoma
  • Hyperthermia:

    Heat has been used for decades to treat cancer. It is best, however, as an adjunct to radiation. It has the ability to enhance the cancer killing injury of the radiation. It works by blocking the cellular repair of daily radiation. The effect is much more pronounced on cancer cells.

    When used, the tumor must be no more than eight cm (3-3 ½ inches) from the skin. Also, hyperthermia must be given within one hour before or after radiation. Additionally, the heat should not be given earlier than 72 hours apart. It is not useful in all cancers. Dr. Tokita will decide if it is of value in your particular cancer.

Frequently Asked Questions

Q: How does radiation work?

A: Radiation is given on a daily schedule (Monday through Friday). Radiation therapy uses high-energy x-rays (ionizing radiation) to stop cancer cells from dividing, it does this by damaging the genetic material within cancer cells. Once this happens, the cancer cells are not able to grow and spread. When the damaged cells die, the body naturally removes them. Normal cells are also affected by radiation, but they are able to repair themselves in away cancer cells cannot.

Within hours, some say within nine hours, 99.9% of normal cells heal that injury. Cancer cells, on average, are thought to take 72 hours to accomplish the same repair. Consequently, radiation must be given daily. As the days progress, the injuries to the normal cells continue to heal, but the injury to the cancer cells accumulate and eventually becomes lethal or fatal to the cancer cell.

The effectiveness of EBRT depends on the difference between the sensitivity of cancer cells and normal cells. Fortunately, many cancers display this difference and allow us to treat those patients. If you have further questions regarding this topic please feel free to ask your radiation therapists or Dr. Tokita.

Q: Can we miss a day of radiation?

A: In general, radiation should be as consistent as possible.

If you need to take a day off, the best days are Mondays, Wednesdays or Fridays. The concept is to not leave any single radiation treatment alone. It is best that the treatments be consecutive, i.e. Monday-Tuesday and take Wednesday off, take Monday off and leave Tuesday and Wednesday together, etc. Talk to the therapists or Dr. Tokita if you need to take a day off.

Q: Why can't you give all the treatment in one day?

A: Part of the answer is in the previous answer. If you give too much radiation in one dose, there will be severe cell injury and cell death. This will include cancer cells and normal surrounding tissue, as well. By giving daily treatments, you preserve that critical advantage of cancer vs. normal cell survival.

Q: Why daily and not on weekends?

A: The treatments are daily so that the cancer cells will accumulate injury and finally begin to die. The normal cells will continue to heal the sublethal injury.

We used to treat seven days a week. In the 1960s and 70s, a group of physicians tried treating six then five, then four days a week. They found that five days a week, was as good as seven days, and the side effects of the radiation were better tolerated. Indeed, we now treat some tumors on a four-day schedule.

Q: What determines the daily dose of radiation?

A: Over the years, we and our teachers have tried many different doses of radiation. Finally, a Radiobiological answer became available to explain the doses that almost all the physicians were coming to. They found that you can give increasing doses of radiation, but at one point you reach a dose that begins to kill cells outright. Any increase from that point led to a rapidly increasing cell death rate and severe radiation injuries.

For curative patients, this dose is 200 cGy (older terminology was Rads), and a common very safe dose in patients with a very high chance for cure would be 180 cGy per day.

Q: What determines the total dose?

A: Different cancers are cured with different doses of radiation.

Q: What is a Radiation Therapist?

A: A Radiation Therapist is trained specifically to treat cancer patients on linear accelerators, simulate and set up patients for treatment using simulators or CT scanners, calculate treatment radiation doses as prescribed by Dr. Tokita and prepare and build the special customized devices prescribed for each patient.

Most importantly, they not only treat patients but also recognize the many things that can happen to a cancer patient undergoing radiation.

Q: What is a Radiation Physicist?

A: A Radiation Physicist has a Masters or Ph.D. degree in a sub-division of physics called Medical Physics. He or she is trained in the use of radioactive materials and accelerators to treat patients. The Radiation Physicist assists and advises Dr. Tokita in accomplishing what is prescribed for the patient. Much of the work is done on treatment planning computers.

Radiation Physicists are also responsible for calibrating the machines, quality control on all equipment and checking the calculations and treatments delivered by the radiation therapists.

Q: We are so excited about finishing Radiation, but have heard about many people are not as happy on finishing as they expected. What is this?

A: As you finish radiation, post-treatment depression is very common. Despite the difficulties one feels with treatment and the anxiousness to finish treatment, it can often be followed by depression. Many cancer survivors have discovered that they experience feelings of fear, anger, sadness and guilt. They may also struggle with their self-image and body image. You may also experience some of these feelings. Some coping strategies include the following:

  • Support groups
  • Cancer Psychotherapists
  • Reading books written by other cancer survivors
  • Talking about your feelings with a supportive spouse, family member or friend
  • Writing about your feelings in a journal
  • The Cancer Center of Irvine has a patient advocacy group, comprised of previous patients
  • Antidepressants can be very useful at this time

Do not hesitate to ask Dr. Tokita for advice and counsel.

In Summary

There are many questions that could be asked. This is an attempt to introduce you to some of the aspects of Radiation Therapy that we are frequently asked about. If you have more questions, please do not hesitate to ask any of the Cancer Center staff or Dr. Tokita.

Your relationship and trust in Dr. Tokita and the staff may go a long way towards maximizing the benefits you receive from radiation.

Thank you for choosing us at the Cancer Center of Irvine.

Kenneth M. Tokita, M.D.
Medical Director