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Tuesday, October 23, 2012

Vagus nerve stimulation in drug-resistant epilepsies. Analysis of potential prognostic factors in a cohort of patients with long-term follow-up.

2012 Oct 21. [Epub ahead of print]

Vagus nerve stimulation in drug-resistant epilepsies. Analysis of potential prognostic factors in a cohort of patients with long-term follow-up.

Source

Institute of Neurosurgery, Catholic University, Largo Agostino Gemelli, 8, 00168, Rome, Italy.

Abstract

BACKGROUND:

The results of vagus nerve stimulation (VNS) for the treatment of drug-resistant epilepsies are highly variable due to the lack of defined patient's selection criteria and a follow-up of published studies being generally too short. Here we report the outcome of VNS in a series with long-term follow-up and try to identify subgroups of patients who could be better candidates for this procedure.

METHOD:

We studied 53 patients (33 male, 20 female) with a prospectively recorded follow-up (mean, 55.96 ± 43.53 months). The monthly average seizure frequency for each patient at baseline, 3, 6, 12 months, and each year until the latest follow-up after implant was measured and the percentage of "responders" and response time (RT) were calculated. We investigated the following potential prognostic role of these factors: age of onset of epilepsy, pre-implant epilepsy duration, etiology, and age at implant.

RESULTS:

Globally, 40 % of patients responded to VNS (mean RT, 14.85 ± 16.85 months). Lesional etiology (p = 0.0179, logrank test), particularly ischemia (p = 0.011, Fisher exact test) and tuberous sclerosis (p = 0.0229, Fisher exact test), and age at implant <18 a="a" age="age" an="an" and="and" associated="associated" at="at" best="best" better="better" duration="duration" epilepsy="epilepsy" implant="implant" in="in" lesional="lesional" logrank="logrank" observed="observed" p="p" patients="patients" pre-implant="pre-implant" response="response" results="results" subgroup="subgroup" test="test" the="the" to="to" vns.="vns." were="were" with="with" years="years">

CONCLUSIONS:

The best candidate to VNS seems to be a patient with lesional etiology epilepsy (particularly post-ischemic and tuberous sclerosis) and a short duration of epilepsy who undergo VNS younger than 18 years.
PMID:
23086106
[PubMed - as supplied by publisher]

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http://www.ncbi.nlm.nih.gov/pubmed/23086106

Monday, October 15, 2012

HEALTHY LIVING: Implant saved my epileptic daughter’s life



Monday 15 October 2012


HEALTHY LIVING: Implant saved my epileptic daughter’s life
Amy Brownhill of Hackenthorpe..whose epilepsy is controlled with an implany..  ..with mum EmmaAmy Brownhill of Hackenthorpe..whose epilepsy is controlled with an implany.. ..with mum Emma
AT the age of six Amy Brownhill was given a new lease of life when she underwent a hi-tech treatment to tackle her debilitating epilepsy, with the help of the Sheffield charity Fable.

Five years on, Star reporter Richard Blackledge caught up with her to find out about her progress and how the good cause is still providing vital information to people with the condition.
AMY Brownhill’s struggle with epilepsy began when she was just over a year old.

But the condition didn’t emerge in the form of a dramatic fit or shocking collapse - instead Amy’s mum Emma noticed her daughter beginning to twitch and jerk as she watched television at their home in Hackenthorpe.

Within months her parents’ fears were confirmed when she was diagnosed, a devastating blow for Emma, aged 36, and her husband Damian, 37.

As her fits worsened, Amy was prescribed medication, but this caused unpleasant side effects - so after receiving help from the Sheffield charity Fable, she underwent a pioneering procedure called vagus nerve stimulation therapy, which aims to reduce the severity of sufferers’ convulsions.

The schoolgirl has now reached the fifth anniversary since her first operation, and Emma believes her daughter may not have lived to her 12th birthday without the treatment.

“If she hadn’t have had it, the worst could have happened, because of the amount of seizures she was having,” she said.

For more than 15 years, Fable - For A Better Life with Epilepsy - has been raising millions through its charity shops in Sheffield, funding nerve stimulation implants and educating the public about epilepsy.

It was set up by city mum Sandra Howard, whose 16-year-old son Gareth became the second, and at the time youngest, person to have an implant fitted successfully.


Although the implants are now more freely available on the NHS, Fable continues to act as an information resource, raising money and holding a monthly epilepsy support group.
“Their advice and support has been above and beyond sometimes,” said Emma.

“I would recommend the implant for anybody with epilepsy. It’s worked for Amy.”

Sandra said she has noticed huge changes in Amy over the past five years.

“She’s just so different now to what she used to be, she was quite withdrawn in the past but now she’s a lot more alert.

“Since the seizures were brought under control it’s made a big difference to her life. It’s been great for us to see her development over the years.”

Amy started having bigger fits - known as tonic-clonic seizures - around five years after diagnosis.
Emma said she contacted Fable after hearing about the success of the VNS implant.

“Amy had been on numerous medications, too many to even think about, and she was always having adverse reactions, like hair loss or mood swings.

“We had to go through approval from the NHS and luckily they didn’t refuse.”

The VNS implant is fitted on the upper left of Amy’s chest wall, just below her shoulder, and is around the size of a watch.

It sends regular electrical impulses to the vagus nerve, which runs from the brain through to the abdomen.

It means that instead of suffering fits, Emma simply sits motionless and stares into space until they pass.

“She’s doing fantastically, she’s had the battery replaced twice now,” Emma said.

“It actually does stop the majority of the seizures before they start.”

Amy, who also has autistic spectrum disorder, has just started in Year 7 at the Talbot Specialist School in Norton.

Emma, who works as a carer for the elderly, and Damian, a senior account manager at an engineering firm, have another daughter, Jessica, 15, who is not affected by epilepsy.

“It’s going to be more difficult as Amy gets older, because she’s going to go through puberty,” Emma added.

“She does get really difficult to control, she has what we call ‘meltdowns’. I do wrap her in cotton wool, but I try not to do anything differently.”

Visit www.fable.org.uk or telephone 0800521629 for more information about Fable.

http://www.thestar.co.uk/news/healthy-living-implant-saved-my-epileptic-daughter-s-life-1-5025555

Thursday, October 11, 2012

[Vagus nerve stimulation therapy in patients with drug-resistant epilepsy and previous corpus callosotomy.]

2012 Oct 6. pii: S1130-1473(12)00097-8. doi: 10.1016/j.neucir.2012.05.001. [Epub ahead of print]

[Vagus nerve stimulation therapy in patients with drug-resistant epilepsy and previous corpus callosotomy.]

[Article in Spanish]

Source

Departamento de Investigación, Centro Latinoamericano de Investigación en Epilepsia-CLIE, Cartagena de Indias, Colombia. Electronic address: cliefire@gmail.com.

Abstract

OBJECTIVE:

To analyse the results of vagus nerve stimulation in patients with drug-resistant epilepsy and previous corpus callosotomy.

MATERIALS AND METHODS:

We prospectively reviewed data from patients with drug-resistant epilepsy who showed persistence of disabling seizures after undergoing corpus callosotomy, in whom it was not possible to identify an epileptogenic focus and who were subsequently treated with vagus nerve stimulation. Variables analysed included: age, gender, aetiology of epilepsy, frequency and characteristics of the crises and Engel scale classification, before and after vagal stimulator implant. Furthermore, the percentage differences in seizure frequency changes were also calculated.

RESULTS:

Four patients were identified: two male and two female. The total seizure frequency had decreased between 20% and 81% after corpus callosotomy in three patients and one of them did not show any favourable response (Engel IVB). Following implantation of the stimulator they became reduced to between 57% and 100% after a mean follow-up period of 8.3 months (range: 3 to 12 months). Generalised seizures decreased between 71.4% and 100%, and focal seizures between 57.7% and 100%.

CONCLUSIONS:

Vagus nerve stimulation therapy proved to be an alternative for the reduction of seizure frequency in patients with drug-resistant epilepsy who suffered disabling seizures despite undergoing corpus callosotomy as primary surgery.
Copyright © 2012 Sociedad Española de Neurocirugía. Published by Elsevier España. All rights reserved.
PMID:
23046918
[PubMed - as supplied by publisher]
http://www.ncbi.nlm.nih.gov/pubmed/23046918

Tuesday, October 9, 2012

Long-term results of vagal nerve stimulation for adults with medication-resistant epilepsy who have been on unchanged antiepileptic medication.

2012 Oct 4. pii: S1059-1311(12)00250-6. doi: 10.1016/j.seizure.2012.09.008. [Epub ahead of print]

Long-term results of vagal nerve stimulation for adults with medication-resistant epilepsy who have been on unchanged antiepileptic medication.

Source

Division of Neurosurgery, Department of Surgery, University Hospital La Princesa, Universidad Autónoma, Madrid, Spain.

Abstract

PURPOSE:

Several studies suggest that vagal nerve stimulation (VNS) is an effective treatment for medication-resistant epileptic patients, although patients' medication was usually modified during the assessment period. The purpose of this prospective study was to evaluate the long-term effects of VNS, at 18 months of follow-up, on epileptic patients who have been on unchanged antiepileptic medication.

METHODS:

Forty-three patients underwent a complete epilepsy preoperative evaluation protocol, and were selected for VNS implantation. After surgery, patients were evaluated on a monthly basis, increasing stimulation 0.25mA at each visit, up to 2.5mA. Medication was unchanged for at least 18 months since the stimulation was started. The outcome was analysed in relation to patients' clinical features, stimulation parameters, epilepsy type, magnetic resonance imaging (MRI) results, and history of prior brain surgery.

RESULTS:

Of the 43 operated patients, 63% had a similar or greater than 50% reduction in their seizure frequency. Differences in the responder rate according to stimulation intensity, age at onset of epilepsy, duration of epilepsy before surgery, previous epilepsy surgery and seizure type, did not reach statistical significance. Most side effects were well tolerated.

CONCLUSIONS:

62.8% of our series of 43 medication-resistant epileptic patients experienced a significant long-term seizure reduction after VNS, even in a situation of on unchanged medical therapy. Patient characteristics predictive of VNS responsiveness remain subject to investigation. Controlled studies with larger sample sizes, on VNS for patients with medication-resistant epilepsy on unchanged medication, are necessary to confirm VNS efficacy for drug-resistant epilepsy, and to identify predictive factors.
Copyright © 2012 British Epilepsy Association. Published by Elsevier Ltd. All rights reserved.
PMID:
23041031
[PubMed - as supplied by publisher]
http://www.ncbi.nlm.nih.gov/pubmed/23041031

Sunday, October 7, 2012

TMS Breakthrough: New Hope for Treating Severe Depression With Few Side Effects


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TMS Breakthrough: New Hope for Treating Severe Depression With Few Side Effects

     

Tuesday, 02 October 2012 09:50 By Robert Wilbur, Truthout | News Analysis

 

A new treatment for major depression - and possibly other maladies, including pain and post-traumatic stress disorder - seems as effective as the alternatives, with lower cost and fewer side effects. Psychiatrists say TMS is showing much promise in preliminary studies.

Until four years ago, psychiatrists had only two options for treating major depression: drugs and electroconvulsive therapy (ETC), formerly known as electroshock.

Antidepressant drugs can take as long as four to six weeks to kick in, and they have many side effects: cardiac toxicity, urinary retention, impotence, loss of libido, blurred vision, dry mouth, somnolence, overstimulation and assorted other complications that vary from drug to drug.

Surprisingly, ECT, which passes an electric current through the brain, is considered to be safer than drugs for patients with many physical illnesses, but it also has a steep downside of its own: A course of ECT can wipe out crucial memories like Ajax scouring out a sink.

Most psychiatry textbooks write that a first trial of an antidepressant is effective only 60 percent of the time. ECT is generally said to be effective 70 percent to 80 percent of the time.

In 2008, the US Food and Drug Administration approved a new device for treating major depression: Transcranial Magnetic Stimulation, or TMS. TMS has its roots in the research of Michael Faraday, the giant of 19th century physics. He could scarcely have dreamed that his law of induction would one day be used to treat mental illness.

Faraday's Law is simple: It states that an oscillating magnetic coil - that is, a coil moving back and forth - generates an electric field. Now if a magnetic coil sets up an electric field inside the brain, the electric field will stimulate the neurons to release brain chemicals called neurotransmitters, of which the three most familiar are serotonin, dopamine, and noradrenaline (although there are dozens more under varying degrees of investigation).

Serotonin is a sedating neurotransmitter; dopamine is energizing; noradrenaline resides somewhere in between. The increased availability of one or more of these neurotransmitters is believed to lift the depression.

The instrument that was approved by the FDA is called "NeuroStar." It is manufactured by Neuronetics for "major depression that does not respond to a trial of an antidepressant drug."
This is very generous labeling by the FDA, and in reality the labeling doesn't amount to much, because once a drug or medical device has been approved for marketing, it can be used by the physician for any indication he sees fit.

Already NeuroStar is being used to treat chronic anxiety, bipolar depression (the depressive swing of manic-depressive illness) and chronic pain. I've also been told the military has bought several TMS instruments for treating post-traumatic stress disorder.

As for "major depression," it is an entity that has paraded through the psychiatric literature under a variety of names, among them: "unipolar depression" (to signify that it is not the depressed phase of manic-depressive - bipolar - disorder), "and "endogenous depression (which is intended to signify that it is a biologically, and probably a genetically driven, disorder)."

The condition is marked by mental symptoms such as low mood and morbid or outright suicidal thoughts, as well as physical symptoms like sleep disturbance, loss of appetite and anxiety.

According to Sue McMonigle, vice president for marketing at Neuronetics, there are currently 424 facilities in the US, ranging from hospitals to private offices that use the device. So far, McMonigle said, about 9,000 people have undergone treatment with TMS.

Small-scale studies indicate it is effective about 70 percent or more of the time - in the same range as ECT, but definitive studies are needed to nail this figure down.

The potential for TMS is enormous. According to the Centers for Disease Control, one American adult in ten suffers from depression, by which the CDC means major depression or the milder condition, dysthymia.

This number does not include manic-depressive (bipolar) patients in the depressed phase. Nor does it factor in all the other psychiatric and neurological disorders for which TMS is already being used.
Truthout spoke with two practitioners of TMS - Dr. Alan Manevitz, clinical associate professor of psychiatry at Weill Cornell Medical School, and Dr. James Halper, MD, clinical associate professor of psychiatry at New York University School of Medicine, who set up the first TMS facility in New York City.

The doctors said that, second to depression, the best-established indication for TMS is pain. They called TMS a "new pathway of treatment" without the problems of antidepressant drugs or ECT.
So exactly what is NeuroStar? Manevitz and Halper invited me to visit their private clinic on New York's chic Sutton Place, where their clinical coordinator, Yoko Kanamori, demonstrated the workings of the Neurostar for me.

The treatment room looks like a dentist's office, with a comfortable recliner and the magnet mounted in an armature, rather like the dentist's drill, that is connected up to a box that allows the operator to adjust the number of magnetic oscillations per second and, applying Faraday's Law of Induction, the strength of the electrical field inside the brain.

The magnetic field is weak - it would take 30 treatments with the NeuroStar to equal the degree of magnetic exposure of a single scan with a magnetic resonance imager (MRI), Kanamori told me.
The business end is the magnetic coil under a padded headpiece that covers the prefrontal cortex, a region of the brain associated with depressive mood and morbid, sometimes suicidal, thoughts. The prefrontal cortex sends and receives bundles of nerve fibers to and from a region of the brain, the limbic system, that is responsible for what are called the somatic or "vegetative" symptoms of depression like disordered sleep, loss of appetite, anxiety and other symptoms not ordinarily amenable to will power (which is one good reason why it is stupid and cruel to tell someone suffering from depression to "snap out of it").

Kanamori switched on the NeuroStar and held the back of my hand against the cushion. I felt a mildly annoying rat-tat-tat of the magnet oscillating back and forth, then a longish respite, followed by another burst of magnetic activity. Not surprisingly, headache is a rather frequent complaint from TMS, but it can be easily treated with Tylenol or aspirin. Otherwise, TMS is largely free of side effects.

The definitive study on the indications and side effects of TMS was conducted last year by a "blue ribbon" panel of experts chosen by French medical societies. After reviewing the literature on TMS, the authors concluded that the only significant side effect was the rare occurrence of seizures, and these occurred as a rule when the practitioner departed from the instructions for using the instrument, or rarely when the patient was taking an antidepressant that lowers the seizure threshold.

In TMS, the patient is fully awake, sitting comfortably in the recliner, and reading or watching a video. There are five sessions a week, and each session lasts for one hour. A complete course of treatment lasts four to six weeks. Since this is about the same as the time it usually takes for antidepressant medication to go to work, what's the advantage of TMS?

First, far fewer side effects. Secondly, some studies show that it works when drugs fail. When the magnet is lifted off the patient's head, out she walks.

The same cannot be said of ECT. Practitioners vary in their methods, but ECT is usually given every couple of days for a total of seven to 10 treatments. The patient is wheeled into the ECT suite on a gurney, where a minimum team of a psychiatrist, an anesthesiologist, and an ECT nurse await him.
The anesthesiologist promptly administers a short-acting anesthetic such as brevital. Next comes succinylcholine, an agent that paralyzes all the skeletal muscles of the body - including the muscles involved in breathing. An ECT nurse at once begins to "bag" the patient, that is, force oxygen into his lungs or else he would soon die.

With the patient all "prepped," the psychiatrist positions electrodes on the temples (or on just one side, if he opts for the unilateral procedure) and hits the "on" button, which sends a jolt of 225-450 volts of electricity through the brain.

Were it not for the muscle-paralytic effects of succinylcholine, the patient would experience violent convulsions that often shattered bones in the past. As it is practiced today, just about all there is to see that suggests a convulsion is a brief bending of the feet.

The ECT nurse continues to bag the patient until he starts breathing on his own; then he is wheeled into the recovery room where he is observed by a nurse until the anesthetic progressively wears off, and he emerges from his experience disoriented and confused.

Today, ECT is almost always administered to hospitalized patients, but there are "buzz shops" to be found that give ECT on an out-patient basis. Usually it takes the patient a couple of hours before she's steady enough to leave, but the patient is usually warned not to drive herself home.

It will probably have occurred to the reader that TMS and ECT have a common denominator: Both set up an electric field within the brain, although TMS delivers the electricity gradually and moderately over a period of weeks, while ECT serves it up in seven to ten flashes of current.

In fact, one of many theories of ECT efficacy is that the electric field releases a torrent of neurotransmitters.

An important consideration in treating depression, and all the more important when the depression is severe, is a feature called the durability - the length of time from the termination of treatment to the return of depressive symptoms.

For antidepressant drugs, the durability is six months to relapse. Skilled psycho-pharmacologists usually maintain their seriously ill patients on medication for two years, then taper the dose very gradually and kick it right back up again at the first hint of a relapse.

Some depressed patients require lifelong medication. I have been using the word "antidepressant" in the singular, but in fact the art of psychopharmacology is often to use drug combinations skillfully.
The most popular and effective adjunct is to add lithium to an antidepressant. This combination is so effective that results are often seen in a matter of days. Another safe and effective adjunct is thyroxine (T3), and the addition of lithium and thyroxine is more effective that either adjunct alone.
Many other drug combinations are used, such as two different categories of antidepressants - for example, a tricyclic like Elavil, and a monoamine oxidase inhibitor like Phenelzine - or the addition of a stimulant, like Ritalin, to an antidepressant.

In recent years, the addition of "second-generation antipsychotics" - Abilify, Seroquel, Zyprexa and other agents that are more than just antipsychotics; they possess antidepressant and anxiolytic properties in their own right - are gaining in popularity as adjuncts.

This far from exhausts the cornucopia of adjuncts that are used in modern psychopharmacology.
Clinical experience over a period of decades has found that ECT has a durability of six months. Most psychiatrists find it prudent to discontinue antidepressant medications before embarking on a course of ECT; once the patient has completed seven to ten treatments, the psychiatrist starts a regimen of antidepressant medication to prolong the durability of the recovery; some psychiatrists, rather than administering medication, give periodic "booster" doses of ECT. Similarly, two or three booster treatments of TMS will usually effect a remission in patients who have experienced a course of TMS and, after a variable period of time, show signs of a depressive relapse.

One advantage of TSM over ECT is that the patient can safely take antidepressants during TSM therapy, a consideration that strengthens its durability.

Memory loss and, sometimes, confusion are the major side effects of ECT - and they can be major, according to Dr. Maria A. Sullivan, a psychiatrist and psychologist at New York State Psychiatric Institute, who uses ECT so infrequently that she couldn't recall when she last employed it. Her view is that ECT should only be administered to the most severely ill patients - those with catatonia and severe, life-threatening depression that does not respond to aggressive pharmacotherapy and psychotherapy.

Other psychiatrists intervene earlier. Thus, Dr. Gabriella Centurion - a psychiatrist in private practice who is a TMS provider - calls ECT the "gold standard" for treating severe depression. Virtually since its introduction, ECT has stirred controversy between therapeutic "doves" and "hawks." An ongoing study at Columbia University, which compares TMS to ECT and which is large enough to overcome the objections to the small, existing pilot studies, may provide definitive information.

So long as they are interpreted cautiously, the existing pilot studies show that TMS and ECT are comparable. If confirmed, these data will have a major impact on the way that we treat severe depression.

What about the bottom line? Fees vary for the treatment. According to Manevitz and Halper, the usual cost for TMS runs from $10,000-$11,000. ECT costs generally run higher, because the treatment requires a three-person team: a course of 12 ECTs comes to about $24,000, according to the Carrier Clinic in New Jersey.

Pills may be the most expensive of all, though, especially if someone has to take a combination of drugs for two years. According to Mark Bausinger, a vice president at Neuronetics, the insurance industry is slow to pick up the tab for TMS, but one by one they are coming on board as they come to appreciate the cost-effectiveness of TMS. This is often the case with new medical instrumentation.
Inexplicably, but not surprisingly, Medicare is divided on the issue. The New England district picks up the tab for a course of treatment. Other districts won't pay a cent. Still others remunerate at such a miserly rate that few psychiatrists are willing to learn how to use TSM and invest in the apparatus.
The failure of Medicare to pay for TMS is yet one more burden on the elderly, who have an even higher prevalence of depression than younger people. With their multiple illnesses and failing memories, our senior citizens are often poor candidates for medication or ECT, but as Kanamori told me, old people tolerate TMS well.

Neuronetics has a special program for TMS patients that helps them to fill out insurance forms to receive remuneration from insurance carriers. Manevitz and Halper reported that, at least in their practice, 75 percent of patients receive some reimbursement from their insurance carriers after taking their case to appeal - but the remuneration often is not adequate, and depressed people may have a hard time coping with the complex appeals procedures of public and private carriers. It will be interesting to see how much - if anything - the Affordable Care Act allows for TMS.

At this point, Manevitz and Halper told me in our three-way phone conversation, major depression and chronic pain are two indications for which TMS therapy is well-supported by the evidence from clinical trials and psychiatric practice.

It is being looked at closely for other indications; some will hold up under the weight of rigorous clinical trials and others will turn out to be disappointing. But right now, hopes are high in the psychiatric community.
 

Robert Wilbur

Robert Wilbur did research in biological psychiatry for many years. He also writes for popular magazines and newsletters. He is active in progressive politics, especially opposition to the Middle East wars and capital punishment, and fighting for animal rights.

http://truth-out.org/news/item/11833-tms-breakthrough-new-hope-for-treating-severe-depression-with-few-side-effects

Friday, October 5, 2012

Vagus nerve stimulator stability and interference on radiation oncology x-ray beams.

2012 Oct 3;57(20):N365-N376. [Epub ahead of print]

Vagus nerve stimulator stability and interference on radiation oncology x-ray beams.

Source

Radiation Oncology Department, Tri-State Regional Cancer Center, 706 23rd Street, Ashland, KY 41101, USA. Regulation Directive Medical Physics LLC®, 3312 Forestdale Court, Flatwoods, KY 41139, USA.

Abstract

Five different models of Cyberonics, Inc. vagus nerve stimulation (VNS) therapy pulse generators were investigated for their stability under radiation and their ability to change the absorbed dose from incident radiation. X-ray beams of 6 MV and 18 MV were used to quantify these results up to clinical doses of 68-78 Gy delivered in a single fraction. In the first part, the effect on electronic stimulation signaling of each pulse generator was monitored during and immediately afterwards with computer interrogation. In the second part, the effects of having the pulse generators scatter or attenuate the x-ray beam was also characterized from dose calculations on a treatment planning system as well as from actual radiation measurements. Some device models were found to be susceptible to radiation interference when placed directly in the beam of high energy therapeutic x-ray radiation. While some models exhibited no effect at all, others showed an apparent loss of stimulation output immediately after radiation was experienced. Still, other models were observed to have a cumulative dose effect with a reduced output signal, followed by battery depletion above 49 Gy. Absorbed dose changes on computer underestimated attenuation by nearly half for both energies amongst all pulse generators, although the computer did depict the proper shape of the changed distribution of dose around the device. Measured attenuation ranged from 7.0% to 11.0% at 6 MV and 4.2% to 5.2% at 18 MV for x-rays. Processes of back-scatter and side-scatter were deemed negligible although recorded. Identical results from 6 MV and 18 MV x-ray beams conclude no neutron effect was induced for the 18 MV beam. As there were documented effects identified in this research regarding pulse generation, it emphasizes the importance of caution when considering radiation therapy on patients with implanted VNS devices with observed malfunctions consequential.
PMID:
23032351
[PubMed - as supplied by publisher]
http://www.ncbi.nlm.nih.gov/pubmed/23032351

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