Sunday, 12 April 2009

Worry beads ...... brain tumour radiosurgery


Understandably enough, I suppose, I have been finding out all I can about the management and treatment of meningioma, particularly regard to radiosurgery, which the neurologist has told me is the most likely course for mine due to its location at the base of the brain. All I can remember from the CT pictures is that it is on the underside of the cerebellum and pressing on part of the brain stem. The MRI scan due at the end of the month will show its exact shape and whether or not it is encroaching on any major blood vessels or other vital structures.

My initial understanding was that my treatment might be by Gamma-knife as I had assumed (wrongly as it turns out) that this was the form of radiosurgery used at Dunedin Hospital but, having researched the subject a bit further, I find that this is not the case and Dunedin uses a different machine and method to that of Gamma-knife.

It certainly can all become very confusing due to the various terms used for describing different forms of cancer treatment, such as radiation therapy, radiotherapy, radiosurgery!! But I think I have got the gist of it now!

RADIATION THERAPY:

Whole brain radiation therapy (WBRT) can target large areas of the brain resulting in neurotoxicity to healthy brain tissue as well as tumour cells. Side effects may be acute (occurring within hours or days of treatment), such as hair loss, nausea, vomiting, severe cerebral oedema (swelling of the brain), or chronic such as brain atrophy, necrosis, neurological deterioration and dementia.

WBRT is the most damaging of all types of radiation treatments to the brain and causes the most severe side effects in the long run. Major studies and research are increasingly demonstrating that alternative forms of therapy, i.e. radiosurgery and stereotactic radiotherapy, can be as effective as WBRT but without the side effects.

RADIOSURGERY:

Radiosurgery is generally taken to mean the delivery of a single targeted radiation treatment to the tumour using narrow beams of radiation delivered from multiple angles. This limits radiation to healthy brain tissue to little or none and takes place in a one-session treatment. It is also called Stereotactic Radiosurgery.

The most common machine for this type of treatment is the neurosurgical instument called Gamma Knife which severaly restricts radiation to the tumour bed with negligable overlap to healthy tissue. Gamma knife is used specifically for radiosurgery to the brain.

Stereotactic radiosurgery can also be undertaken using Linac technology.

Linac is short for the term linear accelerator. Linear accelerator machines produce radiation that is referred to as high energy X-ray. A linear accelerator machine is designed to be a
general purpose radiation delivery machine and in general requires modifications to enable it to be used for radiosurgery or IMRT (intensity modulated radiation therapy). Often, the modification is the addition of another piece of machinery.

Linac machines may be dedicated or non-dedicated. Dedicated linac machines have the additional equipment to perform higher level treatments permanently attached to the radiation couch. This is the preferred method.

Non-dedicated linac machines may be used for conventional radiation therapy in the morning and after adding the attachment, are used for higher level treatments in the afternoon. Non-dedicated linac machines are unable to acquire the same degree of precision and accuracy that dedicated machines may have.

STEREOTACTIC RADIATION THERAPY (also called FRACTIONATED RADIOTHERAPY/SURGERY)

Radiation is delivered with the same precision as in stereotactic radiosurgery but is divided into small, daily fractions over several days or weeks using a relocatable head frame. The intent is to reduce radiation injury to nearby brain structures while maintaining tumour control. The machines that do fractionated treatments are linear accelerator based.

According the International RadioSurgery Association:

"It should be noted that with daily treatments over time there is less accuracy than with one session radiosurgery as the skull cannot be targeted in exactly the same place (repositioned) and manner with each subsequent treatment as it was in the first treatment. IGRT (Image Guided Radiation Therapy) allows for each session to be reimaged before the treatment that can provide more accuracy than without the imaging. All high level linac machines are considered high-level and provide IGRT imaging including the X-Knife, Trilogy, Synergy, Novalis and CyberKnife. These machines would be considered comparable in effectiveness of treatment and outcomes.

However, the most precise, lowest cost and accurate treatment is still with one session radiosurgery."

So my little worries at present are:

a. It would seem that Gamma-Knife is the best method of radiosurgery but this is not an option (nearest Gamma-Knife unit is in Sydney).
No good wishing for the moon then!

b. Dunedin Hospital offers linear accelerator radiosurgery using X-Knife. From the literature it would seem that this is not quite as good as, but is next best thing to, Gamma-Knife.
How lucky that there is a treatment available. However, is it a dedicated or non-dedicated machine?

c. Will the team decision be to go for stereotactic radiosurgery (one session on one day)? Or might they feel that fractionated radio therapy might be more effective?
This might depend on the position of the tumour and what other structures are involved, so I must wait until after the MRI to find out.

d. An IMMEDIATE worry is that my temporary crown repair is falling away and the whole thing is threatening to fall out! .... and I don't see the orthodontist for another 3 weeks!!!!!

HELP!