What is radiation treatment for facial pain?
To treat your facial pain, several types of radiation treatment may be an option for you. First line therapies such as medication may fail to provide relief, may stop being effective, or may cause side effects that you may not want to live with. You may not be a good candidate for MVD surgery, or you may have tried ablative procedures, such as a rhizotomy, that did not keep your pain away. Since the mid 1990’s, radiosurgery and radiotherapy have been used to target portions of the trigeminal nerve to relieve pain.
Despite their names, there is no actual ‘knife’ involved, nor are these surgeries that entail a surgeon cutting into your head. Prior to treatment, your head will be stabilized with either a molded mask shield or a metal frame that is pinned to the skull. The type of stabilization device and the length of treatment depend on the stereotactic radiation machine being used.
Radiosurgery vs. radiotherapy
The difference between stereotactic radiosurgery and stereotactic radiotherapy has to do with the intensity and duration of the radiation treatments. Stereotactic radiosurgery is delivered in a one-day session. It delivers radiation at a very high intensity, all at once, to a small area. Radiosurgery is used for the head and neck because these can be immobilized to ensure the precise delivery of radiation.
Radiotherapy is done over the course of multiple sessions. Stereotactic radiotherapy delivers radiation at different times, at lower intensities and also can be targeted to larger areas.
It is important to understand that some medical centers have access to only one type of machine, so it is important to understand all available options and then decide where to have your treatment. Your doctor should be able to explain all options and help you make an educated decision. To treat your facial pain, your doctor will decide how much of the nerve to target with radiation and what dose to use. An “absorbed dose” describes the amount of radiation absorbed by an object or person. The unit for absorbed dose is the gray (Gy). A gray is the international unit used to measure absorbed dose. The U.S. unit for absorbed dose is the rad. One gray is equal to 100 rads.
How does radiation treatment work?
The theory is that the radiation damages the pain fibers in the trigeminal nerve, and once they are damaged, the pain is either reduced or resolved. The radiation hurts the nerve fibers only a bit, likely because it is injuring myelin insulation, also reducing the electricity that gets to the short circuit in the nerve. The nerve fiber does not work as well when the myelin is injured because the speed of electrical conduction is reduced Because it can take the radiation some time to work, it can take several weeks to months after radiation treatment for the pain to subside.
History of using radiation to treat trigeminal neuropathic pain
Treatment causing injury to the trigeminal nerve to alleviate pain (ablative treatment) was done with other techniques, including mechanical compression of the nerve with balloons, heating of the nerve via radiofrequency rhizotomy, or using glycerol, a form of alcohol, to damage the nerve. Once it was realized that one could damage the nerve and achieve pain relief, it was a simple step to use focused radiation to achieve the same result.
How well does radiation work for facial pain?
For Classical TN, also called Type 1 TN, the initial pain relief is quite high, on the order of 85% chance of complete or partial pain relief. The issue with focused radiation damage is that the nerve attempts to repair the injury, and this can result in the recurrence of pain if the nerves repair themselves. Thus overtime, the pain can come back in some patients. Dr. Steven Chang, FPA Medical Advisory Board member, typically quotes a 50% chance of still having pain relief after radiosurgery after a five-year period.
Atypical TN (ATN), or TN2, is likely a result of a component of permanent nerve injury. With this type of TN, there is an element of constant, usually burning, pain in addition to electrical stabs. That may be why it is harder to treat by microvascular decompression surgery (MVD). For the same reason, it may not be appropriate to treat this type of TN by an ablative procedure such as radiosurgery. That is because the radiosurgery injures an already injured nerve and may make things worse.
Pain relief after radiation compared to MVD
Results of a 2017 study comparing the long-term pain relief rates after first time MVD and stereotactic radiosurgery (SRS), specifically GammaKnife can be found in the Summer 2018 issue of the FPA Quarterly journal. It is important to remember that each person is different and your experience may not follow those of others who have had a particular treatment. It is important to consult with doctors who are experienced treating neuropathic facial pain.
Types of radiation for facial pain
The radiation is generated by two different approaches. Although the names of both types include the word “knife”, radiation therapy does not include cutting, nor is invasive, like surgery.
Gamma Knife for facial pain
Gamma radiation is derived from a fixed source of cobalt radioactivity. The source is contained in a lead box that is opened for a mathematically calculated amount of time. A helmet shaped like the top of an ice cream cone funnels the radiation to a collimated circle of varying widths. For TN, the width of the collimator or tube is less than 1/8 inches in diameter. By adjusting the position of your head so that the targeted trigeminal nerve is at the center of that circle of radiation, dozens of otherwise harmless beams of radiation come together in one “hot spot.” How “hot” the spot gets depends on how long the box is kept open and how much radiation piles in.
It takes 20–45 minutes to reach the planned dose. The targeting is done by computer calculation based on the neurosurgeon identifying the trigeminal nerve on an MRI or computed tomography (CT) scan. This is the most important role of the neurosurgeon, other than placing the frame on the head. Sometimes it is difficult to see the nerve, especially if there has been previous surgery on it, such as MVD.
CyberKnife for facial pain
CyberKnife uses robotic delivery of radiation, and the arc-based system. CyberKnife and arc-based systems generate photon radiation using a small linear accelerator (LINAC) that is turned on by electricity and is not inherently radioactive. The CyberKnife, like Gamma Knife, is not actually a knife either. The technique uses a robot, the same one used to do spot welding of cars when they are built. Instead of shooting lasers, it shoots radiation beams of varying diameters depending on the collimator placed on the accelerator that is piggy-backed on the robot. The robot moves slowly, and the shots of radiation can arrive from many different directions. Each shot has a small amount of radiation, but they add up where they “paint” the target from the different directions.
Both systems ensure that no radiation, or very little, goes through vital and susceptible areas such as the eyes, the optic nerves, or the brain stem.
Why are Gamma Knife and CyberKnife used and not other types of radiation therapy?
The trigeminal nerve is quite small, and the Cyberknife and the Gamma Knife are the two machines that have the ability to accurately target extremely small targets.
Possible side effects
- Numbness in the treatment area; anesthesia dolorosa, or “painful numbness”
- Dysesthesia, or ‘abnormal sensation’ that may be uncomfortable or painful; this may be experienced as burning, prickling, or aching
- Pain recurrence; incomplete pain relief