What is fractionated radiotherapy?
The benefits of radiation are not immediate but occur with time. Aggressive tumors, whose cells divide rapidly, tend to respond quickly to radiation. Over time, the abnormal cells die and the tumor may shrink. Benign tumors, whose cells divide slowly, may take several months to show an effect.
Radiotherapy is split into a number of treatments called fractions that are given over several weeks. Delivering a small fraction of the total radiation dose allows time for normal cells to repair themselves between treatments, thereby reducing side effects. Fractions are usually given five days a week with a rest over the weekend. Therapy sessions often take less than an hour.
The radiation beams are generated by a machine called a linear accelerator. The beams are precisely shaped to match the tumor and are aimed from a variety of directions by rotating the machine around the patient. There are several types of machines, but they all do the same things:
- Precisely locate the target (tumor, lesion)
- Hold the target still
- Accurately aim the radiation beam
- Shape the radiation beam to the target
- Deliver a specific radiation dose
Doctors may recommend radiotherapy as a standalone treatment or in combination with surgery, chemotherapy or immunotherapy. Radiation may be given after surgery to stop the growth of tumor cells that remain. If eliminating the tumor is not possible, radiation can be used to relieve pain, seizures, or other symptoms.
What’s the difference?
RadioTHERAPY
6-33 fractions | Delivers radiation at lower doses, over multiple days, to larger areas. Treats a “margin” or brain tissue around tumors. |
RadioSURGERY
1-5 fractions | Delivers radiation at very high doses, a few times, to a small area. Benefit is its rapid fall-off giving a less dose to normal cells. |
Who is a candidate?
You may undergo radiotherapy if you have a:
- Primary brain tumor: glioma, glioblastoma, astrocytoma, lymphoma
- Benign tumor: acoustic neuroma, pituitary adenoma, meningioma, craniopharyngioma, glomus tumor
- Metastatic tumor: lung, breast, skin, or other cancer that has spread to the brain
Who performs the procedure?
Radiation oncologists are doctors who have special training in treating cancer and other diseases with radiation. The radiation oncologist works with a team that includes a surgeon, medical physicist, dosimetrist, radiation therapist, and oncology nurse. The surgeon and radiation oncologist decide what techniques to use to deliver the prescribed dose. The physicist and the dosimetrist then make detailed calculations and set up the equipment. The radiation therapists position you on the machine and deliver the treatments. The nurse provides care and helps you manage any side effects.
What happens before treatment?
Consultation
Your first appointment is a consultation with a radiation oncologist. They will perform a physical exam and reconfirm your diagnosis based on the imaging studies (CT, MRI) and pathology reports. They will discuss with you the best type of radiation treatment for your particular tumor or lesion, explain the treatment process, and describe possible side effects. Once you’ve decided to go ahead with treatment, you will sign consent forms.
Step 1: create face mask
At your next appointment, a custom-made stereotactic mask will be made to fit your face exactly. It will be used during imaging and each treatment session to hold your head perfectly still. You will lie with your head on a cradle of mesh stretched between a U-shaped frame. Next, strips of stretchy plastic are placed across your forehead, under your nose, and over your chin. You will be asked to bite a small piece of plastic with your front teeth. Next, thermoplastic mesh is dipped into a water bath, making the mesh very flexible. The mesh is placed over the face and allowed to conform. You will be able to easily breathe. Cold mitts help the mesh cool and harden. Creation of the mask takes about 30 minutes.
Step 2: simulation
Once the facemask is created you will undergo imaging scans, called CT simulation, to carefully plan your radiation treatment. Reflective balls are placed on the facemask and worn during the CT scans. These markers appear on the scan and help pinpoint the exact three-dimensional coordinates of the target within the brain. It may be necessary to obtain a new MRI scan.
After the scan, the facemask is removed and you may go home. The doctors continue with step 3 (treatment planning), and you will return within a week or so to begin treatment.
Step 3: treatment planning
Information about the tumor’s location, size, and closeness to critical structures is gathered by the CT or MRI scan. Advanced computer software uses the scans to create a 3D view of your anatomy and the tumor. Using the software, the radiation oncologist, surgeon, and physicist work as a team to determine the:
- Appropriate target or targets
- Radiation dose and number of treatments
- Number and angle of treatment beams
- Size and shape of the beams to exactly match the tumor or target
Each individual beam is too weak to damage the healthy brain as it passes through on its way to the target. But at the intersection of all the beams, the energy dose is strong enough to destroy the tumor.
What happens during treatment?
About a week after the simulation you will return to the center for your first treatment. The nurse or radiation therapist will escort you to a holding room, where you may need to change into a gown.
Step 4: position the patient
After the radiation machine is calibrated and prepared for your specific treatment plan, you will lie on the table. The mask is placed over your face and secured to the table. If you have a head frame, it is secured to the treatment table.
Alignment lasers and x-rays help to position you correctly. Stereoscopic x-rays are taken and compared to the treatment plan. Any misalignments are corrected before treatment.
Step 5: delivery the radiation
The therapist leaves the room and operates the machine from the control room. The team watches you through video monitors and speaks to you over an intercom. The machine and treatment table move every so often to deliver radiation beams from one or more directions.
The machine is large and makes a humming noise as it moves around your head. Its size and motion may be intimidating at first. It may pass close to your body, but it will not touch you. You do not have to hold your breath – just breathe normally. Treatment may take 30 minutes or longer, depending on the complexity of the target.
What happens after treatment?
After treatment the therapist pleases the facemask from the table and helps you get up. The facemask is stored at the center for your next session. You will return each day at your scheduled time to repeat steps 4 and 5 until all fractions of the complete dose are delivered.
Recovery and prevention
Side effects of radiation vary, depending on the tumor type, total radiation dose, size of the fractions, length of therapy, and amount of health tissue in the target area. Some side effects are temporary and some may be permanent. Ask your doctor about specific sides effects you may experience. General side effects may include fatigue, skin irritation, hair loss and swelling.
What are the risks?
Radiation necrosis
In rare cases, radiotherapy may cause the center of the tumor to become necrotic (dead). Radiation necrosis can happen anytime, but it most often occurs 6 to 12 months after radiotherapy. This dying tissue can become toxic to surrounding normal brain, and swelling may occur. Radiation necrosis may look similar to a regrowing tumor on an MRI scan. Special tests such as PET scan or MR spectroscopy/perfusion may help to tell between active tumor and necrosis. However, sometimes these tests are not definitive. Treatment for radiation necrosis may include:
- Medicines that reduce inflammation, 5-LOXIN (Boswellia serrata).
- Hyperbaric oxygen therapy (treatment in an oxygen chamber) may be prescribed to help damaged brain tissue heal.
- A drug called bevacizumab (Avastin) may be given if other treatments are not effective.
- In some cases, surgery may be needed to remove the necrotic tissue.
What are the results?
After all radiotherapy sessions are done, MRI scans will be taken periodically so that your doctors can look for signs of response. Several months may pass before the effects of treatment are visible. Some tumors may be completely eliminated with radiation. For other tumors, the goal is to stop or halt the growth. In some cases the tumor may not shrink, but still be considered “controlled.”
Reach out to the Spine Center specialists at The Iowa Clinic to get all your questions answered or to get an appointment scheduled. Call 515.875.9560 today.