By Jack Hoch
Radiosurgery, or non-invasive, radiation based treatment, is a compelling option for those suffering from diseases of the brain and body to which conventional surgical access is dangerous or impossible. Radiosurgery is not a panacea, but it does have practical applications in specific circumstances.
What is Stereotactic Radiosurgery? Radiosurgery is the application of a high dose of radiation to a specific portion of the body. “Stereotactic” radiosurgery is the use of a three dimensional map (coordinate system) to deliver a predetermined amount of radiation to a precise location in the brain. Normally, it is delivered using a single dose session on an outpatient basis.
According to IRSA ( http://www.irsa.org/radiosurgery.html ) there are three basic types of radiosurgery:
- Particle beam (proton)
- Cobalt60 based (photon)
- Linear accelerator based
Photon-based radiosurgery is commonly known as “Gamma Knife”, as the Gamma Knife machine is the most well-known and has been in use for over 30 years, treating nearly100,000 people over this time period.
Benefits and Drawbacks Each individual's case requires special attention, but generally speaking the following are the most important benefits and drawbacks of radiosurgery:
- Applied in a single session
- Used on an outpatient basis; no lengthy or costly hospital stay
- Minimal “recovery” time compared with conventional surgery
- Documented success for specific applications
- Non-invasive; practically eliminates potential for serious infection
- Any acute side effects are normally transient
- Side effects are not uncommon and include:
- Swelling (edema) – can cause transient neurological symptoms (deficits); sometimes steroid meds are presecribed to combat swelling; worst cases may require placement of a shunt to relieve fluid build-up.
- Necrosis – death of healthy tissue. If any healthy tissue is involved in the irradiated area, deleterious effects on good tissue can result.
- Delayed onset of radiation-induced complications – it may take as long as six to nine months before serious complications result. These complications are more often than not, permanent.
Radiosurgery and Vascular Malformations Radiosurgery has acquired an excellent reputation as the procedure of choice in combating arteriovenous malformations (AVM). Used in conjunction with embolization, dangerous AVMs can be completely eliminated; however, the composition and structure of AVMs are quite different from that of other vascular lesions. The benefits of radiosurgery do not necessarily transfer to other malformations such as cavernous malformations (CCMs), venous malformations, or capillary telangiectasias.
The Controversy of Radiosurgery vs. Microsurgery for CCMs If there is one “lightning rod” topic addressed by the vascular neurosurgery community, radiosurgery vs. CCMs is that topic. While both CCMs and radiosurgery have been around for decades, CCMs are, at best, poorly understood. CCM natural history has only been documented in depth and number within the last 10 years, thanks mostly to the advent of MRI. Medical science has not yet determined the root cause and predictive hemorrhaging behavior of CCMs. Developing a “cure” or a process to deal with an entity of unknown origin and pattern of behavior is problematic at best.
The resultant schism divides most of the neurosurgical community into two camps (assuming we're dealing with an aggressive lesion requiring some type of action, not “expectant management”): those who advocate conventional surgery for CCM removal (the majority), and those who think radiosurgery has a role in the reduction of CCM hemorrhagic potential. There are very few neurosurgeons who take the middle ground by equally favoring both solutions to this issue.
Why the great divide? There has not yet been a 100% conclusive study that radiosurgery is an effective solution. While a few retrospective studies have been done, to date, not one randomized prospective study has been completed. Irrefutable evidence does not exist showing that radiosurgery reduces or eliminates future hemorrhagic events versus the natural history of the disease. Also, there have been cases where longer term results from radiosurgery have been less than ideal, causing patients to seek conventional surgical resection to alleviate persistent symptoms. In many cases, the radiation was a complicating factor, reducing the effectiveness of the follow-on conventional surgery.
Some radiosurgery studies, Gamma Knife studies in particular, indicate that there is a reduction in longer term hemorrhage rate after the procedure [Kondziolka], [Hasegawa], while other studies also show higher complication rates [Steinberg]. Even with Gamma Knife, some complication rates were unacceptably high [Pollock et al]. Pollock and Karlsson both agree that,
“whatever limited hemorrhage protection is provided by radiosurgery is not sufficient to accept the high risk of delayed radiation-related complications associated with radiosurgery of CMs.” [Pollock]
Most importantly, radiosurgery does not remove or obliterate the lesion [Gerwitz et al]. Changes in lesion size cannot be indexed conclusively to radiosurgery. In many cases, lesions are dynamic, and it is impossible to attribute change in size or volume to an external procedure.
One proposed hypothesis attempts to explain why radiosurgery surgery may not be suited for CCMs:
Avoiding the haemosiderin fringe is difficult in practice because of the intimate relationship of the ring to the periphery of the cavernoma and uncertainty in accurately determining the lesion's edge… The haemosiderin fringe surrounding the cavernous malformation is therefore likely to be generously dosed during radiosurgery. [St. George]
In other words, the properties of the “haemosiderin” (aged blood products; “hemosiderin is the American spelling) ring make it difficult to ascertain the exact boundary of where the lesion ends and healthy, albeit hemosiderin stained, brain tissue begins. This is in spite of the fact that:
Most authors agree,without venturing a scientific aetiological basis for their observations, that there is a higher incidence of sub-acute radiation reactions following radiosurgery for cavernous angiomas as compared to AVM or other targets, not withstanding lower recommended marginal doses than employed for AVM targets [St. George].
This report stipulates that despite using lower dosage rates in CCM vs. AVM cases, more radiation-induced complications were seen with the CCM cases.
Finally, neurosurgeons at the Barrow Institute commented on the efficacy of radiosurgery radiosurgery in the treatment of CCMs: “First, radiation treatment of angiographically occult vascular malformations does not 'cure' these lesions. Hence, even after treatment, here is a continued risk of hemorrhage. Radiographic documentation of a lesion eliminated after radiosurgery has yet to be published. Second, the risk of radiation injury is significant and must be considered and compared with the outcomes of conventional surgical treatment of these lesions. Third, patients who had received radiation therapy before surgical resection had the worst postoperativecourse.” [Gerwitz].
On the other hand, conventional surgery in most cases can remove 100% of the lesion. Dramatic improvements in microsurgical techniques and experience now allow successful resection of malformations, which would not have been touched five years ago. There is at least one neurosurgeon who has changed positions in this debate and has stopped performing radiosurgery as the primary means to treat deeply seated cavernous malformations
The downside is that conventional surgery brings with it a longer and non-trivial patient recovery time. In some cases if the lesion is not completely resected, it can and does regenerate. Of course, there are instances where the lesion is both aggressive and surgically inaccessible without undue risk of mortality. It is this subset of patients, when all other alternatives have been considered and discarded, to which Gamma Knife may be most suited.
Until a definitive, randomized, multi-centered prospective study is completed, radiosurgery as a treatment modality for CCMs will continue to polarize the neurosurgical community.
Visit our Stories section for a description of one member's experience of the radiosurgery procedure.
Kondziolka D, Lunsford LD, Kestle JRW: The prospective natural history of cerebral cavernous malformations. J Neurosurg 83:820–824, 1995
Hasegawa T, McInerney J, Kondziolka D, Lee JY, Flickinger JC, Lunsford LD: Long-term results after stereotactic radiosurgery for patients with cavernous malformations. Neurosurgery. 2002 Jun;50(6):1190-7; discussion 1197-8
Steinberg GK, Chang SD, Gewirtz RJ, et al: Microsurgical resection of brainstem, thalamic, and basal ganglia angiographically occult vascular malformations. Neurosurgery 46:260–271, 2000
Pollock BE, Garces YI, Stafford SL, et al: Stereotactic radiosurgery for cavernous malformations. J Neurosurg 93:987–991, 2000
Gewirtz RJ, Steinberg GK, Crowley R, et al: Pathological changes in surgically resected angiographically occult vascular malformations after radiation. Neurosurgery 42:738–743, 1998
E. J. St George, J. Perks & P. N. Plowman: Stereotactic radiosurgery XIV: the role of the haemosiderin ‘ring' in the development of adverse reactions following radiosurgery for intracranial cavernous malformations:a sustainable hypothesis. British Journal of Neurosurgery 2002; 16(4): 385–391
Coffey RJ: Brainstem cavernomas. J Neurosurg. 2003 Dec;99(6):1116-7; author reply 1117