Dr. Hodgens
Image Guided Radiosurgery-"Radio Therapy"
Dr. Hodgens-Medical Director Radiation Oncology Scripps hospital, Co-Director San Diego Gamma Knife Center
Recap of July, 2005
In 1990 I began working with the neurosurgeons at Scripps Hospital in treating many conditions with
radiosurgery/gamma knife other than cancer. One of those conditions is Trigeminal neuralgia, which I began treating
about 15 years ago.
I do much more therapeutic radiology now as opposed to radiation oncology.
The apparatus (gamma knife) is a device for putting a target in a very small specific area. The patient is moved along
in the apparatus until the patient is at the spot in their head (brain) that needs to be radiated. The gamma knife
unit is only used to treat the head.
Around 1990 things began to happen that enhanced the use of the gamma knife, which has been around since the
1950’s: better imaging--CT scan, MRI, and ultra-sound units. They are smaller, faster, with higher capacity of
computers and better hardware outside of the gamma knife system, which all help with the complicated dose
(radiation) problems of years gone by. Better hardware for multi-leaf collimator's (a device for producing a beam of
particles with parallel paths).Then the ability to link all of these. When we do a treatment plan, we will use a CT and
a MRI in the hospital these imaging studies are linked directly to our computer. All the studies are linked together on
our planning computer, so that we can do our radiation’s treatment plan. This is called guided radiation therapy.
When you are in the hospital this helps the surgeon guide the radiation to a specific localized area of the brain, or
with TN a specific area of the Trigeminal nerve. This involves what we call three-dimensional therapy conformal (a
map or transformation in which angles and scales are preserved) radiotherapy, to what we use now, intensity
modulated radiated therapy.
When we get ready for the radio surgery, we look at the CT and MRI then we target the Trigeminal nerve and the
root entry zone where the three areas of the nerve come together.
Remember the TN nerve is not going out from the brain stem, but bringing centric information back to the brain. So,
we treat the root entry zone, or areas around the petrous ridge (part of the temporal bone area).
Q. Is this something you can see? This area is very small, can you see the vessel that is causing the pain?
A. There are certain scans where the MRI/MRA where small vessels can be visualized. That little vessel is one of the
things that neurosurgeons look for when they are going to do the MVD so they can put a soft Teflon pad between
the nerve and the vessel.
Q. What does the radiation do to the nerve?
A. We don’t really know. We know, that the patient retains most of the feeling, taste, touch etc while the pain part
is diminished.In other parts of the body when we do radiation treatment, we see long term effects like what we are
trying to achieve with TN. We think what is happening over time is the small blood vessels in that area whether in a
nerve, a kidney etc. The small blood vessels are gradually closed off because of the long term effects of radiation.
They wind up starving that part of the nerve of its blood. This is just a theory; we still really don’t know what really
happens. Procedure for gamma knife or radio surgery for brain targets.
The first thing is putting the frame on with a plastic wrap box, which is attached to the frame. The Plexiglas box is
only used during the MRI. The frame has metal posts with a little hole in each one where a pin goes. That pin goes
through the skin and anchors in the outer part of the skull. This frame ends up being fixed to the skull, (and it hurts).
The doctor uses a local anesthesia to numb those four spots. Most patients do not have a lot of acute or sharp pain.
When we put the frame on, we use a torque wrench to make sure it is tight enough so that it won’t slip. You will feel
the pressure, it feels like a tight band on your head, the pressure will vary. Some will only feel pressure for fifteen or
twenty minutes, others say they feel it the entire time they are on the table. The fact that there is a fixed frame
allows for extreme accuracy. There is a movement on now to use a plastic mask rather than the posts. The
movement inside the mask has a variation of about 2 mm while the patient is lying there. 2mm is a lot, when you are
working in a 2mm area. That is why I prefer the frame.
The gamma knife itself is 201 radioactive cobalt sources. They are arranged so there is a little tunnel down which
each beam source travels. They all intersect at one spot. That point is fixed in space and is on the target, that 2mm
area of the Trigeminal nerve.
The patient lays on their back in a relatively comfortable position. It takes about 45-60 minutes to get the radiation
needed for the procedure. Some patients even go to sleep. Some times you remember parts of what is happening,
other times patients don’t remember anything. When the frame comes off, some patients have phantom pain. In
most cases the patients say that it still feels like the frame and the pins are still there. For some it takes a half hour
to get rid of that feeling others it may take three or four hours.
Some follow up statistics for the gamma knife treatment at the Center:
Treated 300 patients with TN as of April 2004
263 available for follow-up analysis
the average follow up was 32 months
technique was using a single shot of 4mm targeted in the root entry zone using a 90 gray dose at the max-target
(point)
We do all of our targeting based on MRI/MRA imaging. With the patients in a fixed Leksell head frame.
Occasionally we will do CT scanning. If a patient has a pacemaker they cannot have a MRI.
Then they are sent into the radiology dept. Have a spinal tap done with a contrast put into the spinal fluid, tip them
so their head is down for about twenty minutes which lets the contrast run up into the TN part of the brain. Then
when we image the TN with the CT we can see the target.
Most places will do a second, even three gamma knife treatments if needed. Some times after three or four years
the pain come back and a second procedure is needed.
Our results showed of the 263 follow-ups 26 needed another procedure (10%). The technique was the same as the
first with excellent response.
My philosophy is, if you are not going to give an adequate dose, why treat it at all?
Should be in the range of 70-90 gray, and should be the same the second time around. May be somewhat less the
next time etc.
Using the 90 gray about 50% chance of facial numbness.
After gamma knife, stay on your medicine, usually one to three months, gradually going off of it.
There are other Radiosurgery:
Cyber knife—High beam of x-rays. Done without a frame. (Developed to make cars, to make a spot welds at the
same place every time. May someday be highly effective for TN. Used correctly very good. Novallis—Linac system.
Linear accelerator. Image guided, real time imaging. Synergy—probably never be used for tn synergy—Extra cranial
surgeryTomotherapy—probably never be used for TN Trilogy—Probably never used for TN. All Radiosurgery must
meet the same standards as the gamma knife.
The gamma knife is a non-invasive approach to Trigeminal neuralgia. It is a good thing to have in your choices, along
with other procedures.
Patients who are not good surgical candidates
Patients who have a fear of surgery, or do not desires surgery
If you have already had an MVD, gamma knife is a good second choice.
Gamma knife can be repeated
MVD is still the gold standard.
Return to Home Page
Dr. Hodgens-Medical Director Radiation Oncology Scripps hospital, Co-Director San Diego Gamma Knife Center
Recap of July, 2005
In 1990 I began working with the neurosurgeons at Scripps Hospital in treating many conditions with
radiosurgery/gamma knife other than cancer. One of those conditions is Trigeminal neuralgia, which I began treating
about 15 years ago.
I do much more therapeutic radiology now as opposed to radiation oncology.
The apparatus (gamma knife) is a device for putting a target in a very small specific area. The patient is moved along
in the apparatus until the patient is at the spot in their head (brain) that needs to be radiated. The gamma knife
unit is only used to treat the head.
Around 1990 things began to happen that enhanced the use of the gamma knife, which has been around since the
1950’s: better imaging--CT scan, MRI, and ultra-sound units. They are smaller, faster, with higher capacity of
computers and better hardware outside of the gamma knife system, which all help with the complicated dose
(radiation) problems of years gone by. Better hardware for multi-leaf collimator's (a device for producing a beam of
particles with parallel paths).Then the ability to link all of these. When we do a treatment plan, we will use a CT and
a MRI in the hospital these imaging studies are linked directly to our computer. All the studies are linked together on
our planning computer, so that we can do our radiation’s treatment plan. This is called guided radiation therapy.
When you are in the hospital this helps the surgeon guide the radiation to a specific localized area of the brain, or
with TN a specific area of the Trigeminal nerve. This involves what we call three-dimensional therapy conformal (a
map or transformation in which angles and scales are preserved) radiotherapy, to what we use now, intensity
modulated radiated therapy.
When we get ready for the radio surgery, we look at the CT and MRI then we target the Trigeminal nerve and the
root entry zone where the three areas of the nerve come together.
Remember the TN nerve is not going out from the brain stem, but bringing centric information back to the brain. So,
we treat the root entry zone, or areas around the petrous ridge (part of the temporal bone area).
Q. Is this something you can see? This area is very small, can you see the vessel that is causing the pain?
A. There are certain scans where the MRI/MRA where small vessels can be visualized. That little vessel is one of the
things that neurosurgeons look for when they are going to do the MVD so they can put a soft Teflon pad between
the nerve and the vessel.
Q. What does the radiation do to the nerve?
A. We don’t really know. We know, that the patient retains most of the feeling, taste, touch etc while the pain part
is diminished.In other parts of the body when we do radiation treatment, we see long term effects like what we are
trying to achieve with TN. We think what is happening over time is the small blood vessels in that area whether in a
nerve, a kidney etc. The small blood vessels are gradually closed off because of the long term effects of radiation.
They wind up starving that part of the nerve of its blood. This is just a theory; we still really don’t know what really
happens. Procedure for gamma knife or radio surgery for brain targets.
The first thing is putting the frame on with a plastic wrap box, which is attached to the frame. The Plexiglas box is
only used during the MRI. The frame has metal posts with a little hole in each one where a pin goes. That pin goes
through the skin and anchors in the outer part of the skull. This frame ends up being fixed to the skull, (and it hurts).
The doctor uses a local anesthesia to numb those four spots. Most patients do not have a lot of acute or sharp pain.
When we put the frame on, we use a torque wrench to make sure it is tight enough so that it won’t slip. You will feel
the pressure, it feels like a tight band on your head, the pressure will vary. Some will only feel pressure for fifteen or
twenty minutes, others say they feel it the entire time they are on the table. The fact that there is a fixed frame
allows for extreme accuracy. There is a movement on now to use a plastic mask rather than the posts. The
movement inside the mask has a variation of about 2 mm while the patient is lying there. 2mm is a lot, when you are
working in a 2mm area. That is why I prefer the frame.
The gamma knife itself is 201 radioactive cobalt sources. They are arranged so there is a little tunnel down which
each beam source travels. They all intersect at one spot. That point is fixed in space and is on the target, that 2mm
area of the Trigeminal nerve.
The patient lays on their back in a relatively comfortable position. It takes about 45-60 minutes to get the radiation
needed for the procedure. Some patients even go to sleep. Some times you remember parts of what is happening,
other times patients don’t remember anything. When the frame comes off, some patients have phantom pain. In
most cases the patients say that it still feels like the frame and the pins are still there. For some it takes a half hour
to get rid of that feeling others it may take three or four hours.
Some follow up statistics for the gamma knife treatment at the Center:
Treated 300 patients with TN as of April 2004
263 available for follow-up analysis
the average follow up was 32 months
technique was using a single shot of 4mm targeted in the root entry zone using a 90 gray dose at the max-target
(point)
We do all of our targeting based on MRI/MRA imaging. With the patients in a fixed Leksell head frame.
Occasionally we will do CT scanning. If a patient has a pacemaker they cannot have a MRI.
Then they are sent into the radiology dept. Have a spinal tap done with a contrast put into the spinal fluid, tip them
so their head is down for about twenty minutes which lets the contrast run up into the TN part of the brain. Then
when we image the TN with the CT we can see the target.
Most places will do a second, even three gamma knife treatments if needed. Some times after three or four years
the pain come back and a second procedure is needed.
Our results showed of the 263 follow-ups 26 needed another procedure (10%). The technique was the same as the
first with excellent response.
My philosophy is, if you are not going to give an adequate dose, why treat it at all?
Should be in the range of 70-90 gray, and should be the same the second time around. May be somewhat less the
next time etc.
Using the 90 gray about 50% chance of facial numbness.
After gamma knife, stay on your medicine, usually one to three months, gradually going off of it.
There are other Radiosurgery:
Cyber knife—High beam of x-rays. Done without a frame. (Developed to make cars, to make a spot welds at the
same place every time. May someday be highly effective for TN. Used correctly very good. Novallis—Linac system.
Linear accelerator. Image guided, real time imaging. Synergy—probably never be used for tn synergy—Extra cranial
surgeryTomotherapy—probably never be used for TN Trilogy—Probably never used for TN. All Radiosurgery must
meet the same standards as the gamma knife.
The gamma knife is a non-invasive approach to Trigeminal neuralgia. It is a good thing to have in your choices, along
with other procedures.
Patients who are not good surgical candidates
Patients who have a fear of surgery, or do not desires surgery
If you have already had an MVD, gamma knife is a good second choice.
Gamma knife can be repeated
MVD is still the gold standard.
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