Radiosurgical AN Treatments:
Options and Terminology

I. Classifying radiosurgical AN treatments
II. Some radiosurgical options and terms


I. Classifying radiosurgical AN treatments

Every radiosurgical AN treatment can be classified along three dimensions: Radiation/Positioning/Dosage (R/P/D).  The following table shows the different options available along each dimension:

R: Type of radiation* P: Method of accurate (re)positioning D: Dosage, or protocol**
G - Gamma rays
L - LINAC, or electron particles
P - Proton beam

*Peacock treatments, or IMRT, though often mentioned as a distinct option, are actually a variation on LINAC;  we do not list it separately. 

S - Screw-on head frame
F - Custom-made facial mask
D - Custom-made dental mold
P - Pins implanted in the head
C - Cyberknife
1 - Single-session
2 - 2 or 3 sessions over 2 days
3 - 4 to 6 sessions over 1 to 2 weeks
4 - 25 or 30 session over 5 or 6 weeks

**Protocols 2-4 are all fractionated, which simply means "more than one session", and any stereotactic radiation treatment using these protocols can be referred to as "FSR". 

The various radiosurgical treatments for ANs can be described by their R/P/D code.  For example, Gamma Knife, which is the oldest and best known of radiosurgical AN treatments, has code G/S/1: a single-session treatment by Gamma Rays with a screw-on head frame. There are 3 x 5 x 4 = 60 possible R/P/D code combinations.  In principle, each combination produces a different treament. In practice, only some of the combinations are available. 

The following grid shows all the combinations that we are aware of.  The type of radiation is shown along the top, the dosage is shown on the left, and the positioning method is inside. When it's blank, then we are not aware of any treatments of this type;   when there is a question mark, such treatments exist, but the exact positioning option is not known to us.

  Gamma Knife [G] LINAC [L] Proton Beam [P]
1: Single-session S ? ?
2: 2 days   S  
3: 1 or 2 weeks S F,D,P  
4: 5 or 6 weeks   D (offered at Loma Linda)

The FSR treatment that is most common, according to our Radiosurgeon Directory, is L/*/4: 5 or 6-week treatment with LINAC (* is used to indicate "any option"). However, L/FD/3, which is a 4-6 session LINAC treatment with a relocatable headframe (either a facial mask or a dental mold), is rising in popularity.

Each treatment has its own advantages and disadvantages; for example, here is a discussion of G/S/1 vs. L/FD/3. Some combinations have a better track record than others.  Some, such as G/S/3 or */C/*, are still too new to have a track record. Track records of different treatments are a controversial topic.  For the NIH, only G/S/1 has a track record long enough to be worth mentioning. There are also cost differences between the options: while a LINAC machine is inexpensive (several thousand dollars), a Proton Beam facility is a major undertaking (millions of dollars).  Gamma Knife falls somewhere between these two.

In every case, the treatment is stereotactic, meaning that the radiation field is concentrated right on the tumor and is very weak in other parts of the brain. This is accomplished by having rays converge on the tumor, according to a treatment plan that is calculated with the help of a computer, based on a patient's MRI and CT scans.


II. Some radiosurgical options and terms

Stereotactic radiation

Stereotactic means that many rays converge on one point, as in Gamma Knife, or by having one ray move in an arc, with the tumor at the center (as an example of non-stereotactic radiation, think of x-ray machines). This means that the radiation field is concentrated right on the tumor and is very weak in other parts of the brain.

Radiosurgery vs. radiotherapy?

Radiosurgery used to mean single-session radiation-based treatment, and radiotherapy meant multiple-session treatment. So technically stereotactic radiotherapy implies that it's fractionated, and there are people who use  this term instead of FSR (fractionated stereotactic radiation). But until very recently, all stereotactic treatments were radiosurgeries (single-session), so to emphasize the change to a multi-session protocol, "fractionated" is used in addition to, or instead of, "radiotherapy".

Fractionated Radiosurgery

Fractionated means that instead of a single session, the radiation is broken up into smaller doses delivered over several separate sessions. This has been done for cancer treatments for a long time, since the tumor tissue responds more readily to radiation that the healthy tissue. When treatment is fractionated, any single dose is too small to hurt healthy tissue but between them all, the unhealthy tissue is deactivated.  These protocols are newer than the single-session ones, here is more info.

IMRT

IMRT, Intensity Modulated Radiation Therapy, is a treatment which uses a device called the Peacock System, a multileaf intensity modulating collimator that can be attached to a standard linear accelerator, Linac. As the delivery head of the LINAC rotates around the patient, the Peacock attachment is able to divide the Linac's radiation beam into thousands of very thin beamlets which are cross-fired at varying intensities so that they conform to the tumor's exact shape, size and location. It's called Peacock because of the manner in which the radiation fans out, like the tail of the peacock.  Radiation can be delivered single dose or fractionated into 20 to 30 sessions.  Manufactured by NOMOS, Inc. (http://www.nomos.com), FDA approved in 1996.

Apparently, IMRT does not help for smaller tumors.  Here is a patient's account:

In an attempt to get an unbiased opinion, I sent my mothers MRI's to Cleveland Clinic who uses Gamma Knife, FSR and IMRT radiation equipment. A doctor there told me that he would use standard FSR treatments rather than IMRT. He said that due to the relatively small area to be treated there would be no benefit to using IMRT. The doctors at Johns Hopkins and Staten Island had told us the same thing when we asked them (but they don't have IMRT).

Cyberknife

The Cyberknife is a new high-technology system that delivers LINAC radiosurgery using a robotic arm controlled by an image-guided computer technology similar to that used by the military in cruise missiles. The Cyberknife was approved by the FDA in July 1999. Here is more info.

BrainLab

BrainLab is the name of one of the companies that manufactures technology for FSR treatments with LINAC. The BrainLab technology includes:

- treatment planning system (software and hardware)
- mask system (for exact positioning of the head during treatment)
- "M3" (mini-multi-leaf collimator that shapes the beam)

Novalis, a LINAC based radiosurgical machine made is Varian and used at some centers, uses BrainLab software. The John Hopkins Radiosurgery Program is one such center. BrainLab technology is always being improved; current projects include the digitized video system for visualization of the facial contour vs. the mask.

Multi-fraction Proton Treatment

The are not enough patients who have had this treatment, for which the premier facility is at Loma Linda, to make concusive judgements;  however, it seems that the Multi-fraction Proton Treatment causes more side effects than other fractionated radiosurgery methods. Patients with ANs over 2cm might experience serious problems that are more similar to surgery patients with huge tumors than anything else. Here is one such story, dated November 2002:

2.4cm left-side AN treated w/Proton at Loma Linda March-April 2002. Post-treatment, steroids in June-August 2002 for edema, dizziness, nausea. 6.5mos after treatment in Mid-Nov 2002, onset of double vision, photosensitivity, dizziness, nausea, severe headaches. Treated with steroids, still on steroids. New symptoms from Nov. 19: severe generalized numbness in left side of face, problems with left eye not tearing well, hoarseness in voice. Nov. 12 MRI shows tumor shrinkage of 10% from October 2001 MRI. Edema still present in MRI... I can't work or do much else. [Doctors at] Loma Linda are at a loss to know what to do with me.

This story is similar to other Loma Linda cases we have heard, and probably explains why they no longer accept AN patients with tumors over 2cm.

Last Edited: Monday, November 17, 2003