Radiation therapy must be aimed precisely at the treatment target to maximize the treatment efficacy and safety. To accomplish this, your radiation team will perform a “planning” or “mapping” session called a CT simulation. During the CT simulation, a radiation treatment planning CT scan is obtained to get an accurate mapping of your organs while you are in the same position you will be treated in each day. That map will be combined with information from your biopsy, imaging and physical exam and later used to design a radiation plan specific to your needs.
Prior to the simulation, you may be asked to undergo additional procedures or tests. Click here to learn more.
These include:
In preparation for your pre-treatment mapping scan, you may also be asked to follow some instructions to ensure the day goes smoothly. One of the most common requests is that you try to have a relatively full bladder and/or empty rectum at the time of your CT simulation (and every day that you come in for your treatments). The amount of urine in your bladder, and stool in your rectum, can also affect the position of the prostate. Please ask your radiation oncologist for the specific instructions that are being recommended for your treatment.
Radiation treatment planning begins with a CT simulation.
Patients receiving brachytherapy also undergo a simulation, though the process is different. Please see the section titled “brachytherapy” below for more information. For external beam radiation therapy (add hyperlink to section below), this consists of a CT scan done in the exact same position you will receive your actual treatments. To accomplish this, your radiation oncology team may use personalized support devices such as molds, casts, headrests or other devices that are customized to help you remain in the same position and stay comfortable during the entire treatment. Once the scan is complete, the radiation therapist, under the radiation oncologist’s supervision, marks the area to be treated on the personalized support devices and/or your skin with either a bright, temporary paint or a set of small, permanent tattoos.
Patients receiving brachytherapy also undergo a simulation, though the process is different. Please see the section titled “brachytherapy” for more information.
After your CT simulation, the radiation oncologist, dosimetrist, and medical physicist will use sophisticated computer software to design your radiation treatment plan. After this, several quality assurance steps are taken to make sure that the machine that is used to administer the radiation will be able to deliver the treatment accurately. Once these steps are completed, you will be brought back to the radiation oncology department to start your treatment.
Click here to learn more about Treatment Planning and Quality Assurance.
Once you have finished simulation, your radiation oncology treatment team will begin creating a specific radiation plan for your cancer. To do this, your team will review information obtained during simulation along with your previous medical tests. Next, your radiation oncologist will write a prescription that outlines exactly how much radiation should be delivered to specific parts of your body. An ideal radiation plan is one that focuses the radiation on the prostate and other targets while limiting radiation to healthy organs.
Your information is then transferred to a computer system called the treatment planning system (TPS), which is a sophisticated treatment-planning computer and associated software designed to create the best possible treatment plan. A team of experts including your radiation oncologist, medical physicist and dosimetrist will work together to develop the radiation treatment plan.
The radiation oncology team uses the images obtained during the simulation to outline both the areas we want the radiation to be directed (known as targets) and the areas we want the radiation to avoid (known as organs at risk [OAR]). For patients being treated for prostate cancer, the target typically includes the prostate or prostate bed (the area where the prostate used to be after it was removed during a prior surgery). Depending on the extent of the cancer, the radiation targets can also include the seminal vesicles (glands on the back of the prostate) and lymph nodes that drain the prostate. The organs at risk that are typically accounted for include the bladder, rectum, small bowel, sigmoid colon, femoral heads, penile bulb, and genitalia. Ask your doctor to explain what treatment area is appropriate for you.
Sometimes, images taken at other points in your treatment journey may be better suited to determine the extent of your cancer. Specifically, some patients with prostate cancer undergo Magnetic Resonance Imaging (MRI) and/or Positron Emission Tomography (PET), as indicated, during the evaluation of their prostate cancer. During a process called image fusion, your radiation oncologist can align these additional images with those taken during the simulation to get a better understanding of where the radiation should be targeted.
Radiation therapy for prostate cancer is most commonly delivered with photons via a process called External Beam Radiation Therapy. Click here to learn more about how radiation is delivered.
Once your radiation oncologist approves the radiation therapy plan developed in treatment planning, members of the radiation treatment team work together to ensure that your specific treatment plan works correctly on the linear accelerator before treatment begins. Typically, this process also includes an evaluation of the radiation plan where the plan is delivered to a phantom, a radiation monitor with sensors, where the actual amount of radiation from the machine is compared to what was calculated by the computer to ensure they are similar.
Your radiation therapy team may also perform a ‘dry run’. During this process, you will be asked to come in before your radiation is scheduled to start. When you come in, the treatment team will put you on the radiation table and place you in the intended treatment position. This is often needed for more complex treatments to ensure that the radiation treatment designed for you is as accurate and as safe as possible.
During radiation treatment planning, a radiation treatment plan is developed to deliver treatment to your cancer. In most cases, the radiation comes from outside your body, and is called “External Beam Radiation Therapy”. This external radiation is most commonly delivered in the form of high-energy photons, or X-rays. In a few clinics around the country, proton beam therapy is also used to treat prostate cancer. Proton therapy is a form of external beam radiation therapy that uses protons rather than photons to treat cancer cells. Protons may be considered for certain patients. The differences between protons and photons in treating prostate cancer continues to be studied.
External beam radiation therapy can be delivered using a variety of techniques. A common technique used to treat prostate cancer is intensity-modulated radiation therapy (IMRT).
With all external beam therapy, treatment is delivered in a series of daily sessions, Monday through Friday, for several weeks. Each treatment is non-invasive, painless and similar to a long X-ray. You may hear noise but will feel nothing at the time of treatment. Immediately prior to each treatment, your treatment team will ensure the areas designed to receive the radiation are indeed in the correct position. This process initially starts with making sure you are properly set up on the table. This may involve using lasers within the room and aligning them to markings put on your skin and/or the personalized support devices. Next, your radiation therapists might take a set of pictures to confirm that your internal anatomy is properly aligned. This is called Image Guided Radiation Therapy. This may consist of a set of x-rays taken at specific angles or images taken throughout a partial or complete rotation around your body (often called a Cone Beam CT). These images are compared against your images taken at the time of your simulation to make sure your position is accurate.
The length of your treatment will depend on your health and the type of radiation used. Hypofractionated radiation is a form of external beam treatment giving slightly higher doses over four to six weeks compared to a more standard treatment time of seven to nine weeks. Studies have shown similar results compared to standard treatment times. Stereotactic body radiation therapy (SBRT) is a technique for treating cancers in five treatments or less at substantially higher doses per treatment over 1-3 weeks. SBRT is currently being studied for long-term side effects and may be considered for certain patients.
The information on this site was created by our medical advisory board made up of physicians and other members of the radiation oncology team with expertise in radiation therapy and on the topics presented. However, this material is informational only and should not be used in place of advice from a medical professional. If you have questions about a specific treatment, please ask your radiation oncologist.