SRS - Stereotactic Radiosurgery

Guidelines prescribe a dose. No guideline names a manufacturer.

Radiosurgery delivers a high dose to a small target in one session or a few. We deliver it on a linear accelerator, and this page says plainly which machine we own, what it does well, and where we would send you somewhere else.

What stereotactic radiosurgery is

Nothing is cut. The word surgery survives from the 1950s and misleads almost everybody who meets it, because there is no incision, no anesthetic and no blood. What happens instead is that many weak radiation beams enter the head from many directions, cross at one point, and deposit a dose at that crossing high enough to stop the target growing while each individual beam leaves the tissue it passed through largely unharmed.

Precision is the whole trick.

Ordinary radiotherapy spreads a moderate dose over many weeks and accepts that healthy tissue around the target takes some of it. Radiosurgery does the opposite, concentrating a large dose into one or a few sessions with a dose gradient so steep that a few millimeters outside the target the radiation has already fallen away. That steepness allows a single treatment of twenty grays or more, and it explains why everything in this field turns on how accurately the target has been drawn and how accurately the patient can be held still. Everything downstream of those two things follows from them. A target outlined three millimeters too generously delivers a punishing dose to healthy brain that had no reason to receive it, a target outlined three millimeters too tightly leaves living tumor sitting just outside the high dose region where it will quietly carry on growing, and a patient whose head shifts two millimeters during delivery has converted a carefully built plan into a different plan that nobody checked. So the couch time is the short part. Weeks of outlining, physics and verification stand behind the half hour you actually spend lying still.

A dose before it is a machine

Patients researching this treatment meet three brand names within ten minutes and then spend weeks trying to work out which one is best, and that question has a less satisfying answer than the internet suggests, which is fortunate, because understanding why saves a great deal of anxiety and sometimes a great deal of money.

What the trials and the guidelines actually specify

Read the randomized trials on this page and you will find prescriptions written as numbers. Twenty two grays to the edge of a lesion under four milliliters. Twenty grays for one between four and ten. Eighteen to twenty four grays in the trial comparing radiosurgery with and without whole brain treatment. The international guideline that pooled thirty two randomized trials recommends stereotactic radiosurgery as a technique and names no manufacturer anywhere in its recommendations. Physics decides whether a plan meets that prescription, and several very different machines can meet it.

Which does not mean the machines are identical. It means the question to ask a center is whether its plan meets the prescription your case calls for, measured against the published dose constraints, and not which logo is on the gantry.

What we use it for

Brain metastases make up the largest share of radiosurgery anywhere in the world, and they make up the largest share here. One lesion or several, treated in place of whole brain radiotherapy where the evidence supports that choice, and treated to the surgical cavity once a metastasis has been removed.

Beyond that, the usual intracranial list. Small meningiomas, or ones sitting where surgery would cost a nerve, or ones that have come back after an operation. Vestibular schwannomas. Pituitary adenomas that keep growing after surgery. Arteriovenous malformations, where the closure takes two to three years and the choice between radiosurgery and an operation deserves its own conversation. Trigeminal neuralgia that has stopped answering to medication.

Outside the head the same physics treats small lung tumors, liver lesions, spinal metastases and a short list of others, delivered over one to five sessions and carrying the name stereotactic body radiotherapy.

What unites that list is a target small enough to draw a line around and important enough that the tissue beside it must be spared, so where a tumor has no clear edge, or where the disease has spread across a region, this is the wrong tool no matter how good the machine is. That single distinction settles most of the referrals we decline.

The machine we use

Our radiosurgery runs on an Elekta Versa HD linear accelerator. A linear accelerator produces a photon beam, shapes it with a bank of moving metal leaves, and swings around the patient on a gantry so that beams arrive from many angles while the leaves reshape the opening continuously.

The specifications that matter for small targets

Three numbers do most of the work, and a published commissioning study of this machine reports all three. The collimator carries 160 leaves in 80 opposing pairs, each projecting five millimeters wide at the treatment point across the whole bank, which lets the beam shape hug a small irregular target, and the flattening filter free beams run at 1400 monitor units a minute at six megavolts and 2400 at ten, so a large dose goes in quickly and the patient spends less time holding still. Mechanical accuracy in that study came in within one millimeter for the gantry and within seven tenths of a millimeter for the collimator and the couch.

Why the leaf width gets quoted so often

Leaf width sets the resolution of the beam shape in the same way pixel size sets the resolution of a photograph. Five millimeters across the entire bank is a genuinely fine setting for a linear accelerator, and it is the reason a machine of this class handles targets of a centimeter or two without difficulty. It also marks the honest limit to quote when somebody asks how small a lesion we can treat well.

What we do not have

We do not have a Gamma Knife. We do not have a CyberKnife. Saying so on our own website is unusual, and we would rather you read it here than discover it after booking a flight.

When that difference is worth traveling for

Dedicated stereotactic systems earn their reputation on the smallest and most awkward targets. Both machines serve stereotactic work and nothing else, and their collimation goes finer than any general purpose linear accelerator, ours included, can be made to manage. For a very small target sitting hard against a structure that tolerates almost no dose, a few millimeters from an optic nerve or inside the brainstem, that extra sharpness can matter and a dedicated unit is a reasonable thing to seek out. Numbers of targets past a certain count, and some functional treatments such as tremor, also sit more naturally on those platforms. When your case reads that way we will tell you, and we would rather lose the referral than treat you on the wrong side of a real technical line. The line exists. Our position holds that marketing has moved the line until patients believe it runs through the middle of every case, when in practice it runs through a narrow band of them, and the way to find out which side of it you fall on is to send your imaging to somebody who will look at the actual measurements of your actual lesion.

For the great majority of what walks through this department, the line does not bite.

The trial that changed practice

For decades a patient with a few brain metastases got whole brain radiotherapy, on the reasoning that treating the whole organ catches the lesions nobody can see yet. It does catch them. A trial reported in 2016 asked what that catching costs, randomizing 213 patients with one to three brain metastases across 34 centers to radiosurgery alone or radiosurgery followed by whole brain treatment, then testing memory, attention and processing speed three months later.

Both halves count. Whole brain radiotherapy works and it costs thinking, radiosurgery preserves thinking and accepts more new lesions later, and since survival did not separate, the trade became a real choice instead of an obvious one.

Practice moved after that paper, and it moved in one direction. Radiosurgery became the default for a limited number of metastases in a patient well enough to benefit, with whole brain treatment held back for situations where the count or the pattern of disease leaves nothing else sensible. What the trial did not do was abolish whole brain radiotherapy, and a department that speaks about it as an outdated cruelty is overstating a result that plainly showed better control inside the skull when it was added. The decision belongs to your case, your count, your performance status and your own weighting of memory against the odds of a new lesion in eight months.

How many lesions is too many

A number used to circulate in clinics. Three lesions, or four, and beyond that only whole brain radiotherapy. Where that number came from was the entry criteria of old trials rather than any biology.

What 1,194 patients showed

A Japanese study enrolled 1,194 patients across 23 facilities and compared survival by the number of lesions treated with radiosurgery alone. Median survival came to 13.9 months for one tumor, 10.8 months for two to four, and 10.8 months for five to ten. The comparison between the group with two to four and the group with five to ten met its non inferiority threshold comfortably, with treatment related adverse events occurring in 8 percent overall and serious ones in roughly one in forty.

Total volume turned out to matter more than the count. Every lesion in that study was under three centimeters across and under ten milliliters, with a cumulative limit of fifteen milliliters, so what the result really says is that ten small lesions behave like three small lesions. Ten large ones are a different question, and the honest answer there is that treating ten separate targets on a general purpose linear accelerator takes a long session and the planning grows awkward.

After surgery, the cavity still needs treating

Removing a brain metastasis leaves a hole. Microscopic tumor around the edge of that hole explains why a proportion of them come back in exactly the same place, which is the single most frustrating pattern in this disease and the one that postoperative radiosurgery was designed to interrupt.

Radiosurgery to the cavity, against watching it

A randomized trial put 132 patients with one to three completely removed metastases into radiosurgery of the cavity or observation, and freedom from recurrence at that site after twelve months reached 72 percent with radiosurgery against 43 percent with observation, a hazard ratio of 0.46, with no treatment related death in either group. The gap is wide. It is also the kind of gap that changes a recommendation rather than merely decorating a paper. Treatment follows within a month of the operation, once the wound has healed and the cavity has settled to something a planner can draw around.

Which is where our two departments meet

Neurosurgery and radiation oncology sit on the same campus here, so a patient whose metastasis is removed one week can have the cavity planned and treated a few weeks later without changing hospitals, and the surgeon who made the cavity is available to the planner who has to outline it.

What the guideline recommends

Three organizations covering oncology, neuro oncology and radiation oncology published a joint guideline built on 32 randomized trials. Reading the recommendations in the original repays the effort, and the handful of lines that decide most consultations in this department run short enough to state right here.

Every line above rests on pooled randomized evidence, and that deserves saying out loud, because a great deal of what patients are told about radiosurgery rests on nothing sturdier than the preference of whoever happens to be speaking.

The recommendation people find hardest

The same guideline states that patients with no symptoms from their brain lesions, a very low performance status and no systemic treatment options left do not derive benefit from radiation therapy, and reading that sentence about somebody you love is difficult, and a center that quietly treats anyway, because treating is what a radiotherapy department does, has not done them a service. Nobody enjoys that conversation. Having it is the job.

What happens on the day

Treatment day turns out to be the least eventful part of the whole process, and patients who have braced themselves for something surgical often describe a mild sense of anticlimax walking out of the department afterward. The work that made the day possible happened over the preceding two weeks, in a planning room, between people you never meet. The sequence runs from the mask to going home.

1. The mask, about a week earlier. A sheet of thermoplastic is warmed, laid over your face and shoulders, and sets hard in roughly half an hour. It holds your head in the same position every time, and it is snug rather than painful.
2. Planning scans. A CT in the mask, fused with a fresh MRI. The fusion of those two is where accuracy is won or lost, so it is checked by more than one person.
3. Planning, one to two weeks. A radiation oncologist outlines the target and every structure to be protected. A medical physicist builds and verifies the plan, and the plan is measured on the machine before any of it reaches you.
4. Treatment day imaging. You lie on the couch in your mask and a cone beam CT is taken. Position is corrected in translation and rotation until the anatomy matches the plan.
5. Delivery. The gantry moves around you while the leaves reshape the beam. You feel nothing at all, you hear the machine, and a single target usually takes around half an hour on the couch.
6. Home the same day. No anesthetic and no recovery ward. Most people drive home or go back to a hotel and eat a normal dinner.

Why a mask instead of pins in the skull

The older technique screwed a metal frame into the outer table of the skull under local anesthetic, which fixed the head absolutely and made everything happen in a single day. Modern mask systems reach comparable accuracy when the position is checked with cone beam imaging before and during treatment, and they allow a dose to be split across several sessions, which a bolted frame makes impractical. Comfort is a real gain, and the ability to fractionate is the larger one.

Questions worth asking any center

Every question below has a short factual answer, and a center that treats radiosurgery patients regularly can give all five without leaving the room. Ask them of us and ask them of anyone else you are considering.

• What dose are you prescribing, to what volume, and which published constraint are you checking it against?
• How do you verify my position on the day, and is the check repeated during treatment or only before it?
• Who outlines the target, who checks that outline, and is the plan physically measured on the machine itself before my first session begins?
• Given my lesion size and location, would a dedicated radiosurgery platform give a meaningfully better plan?
• What is the expected rate of radiation necrosis at this dose and volume, and how would you treat it?

The fourth one is the test.

One session or several

Strictly speaking, radiosurgery means one session. Splitting the dose across two to five sessions is stereotactic radiotherapy, and in ordinary conversation the two names blur together.

What decides which you get

Three sessions is not a worse treatment. It is the same dose arranged so the tissue around your target survives it.

Size and neighbors decide it. A small lesion away from anything delicate takes a single large dose well, while a lesion above roughly two and a half to three centimeters, or one pressed against the optic apparatus or the brainstem, carries a higher risk of the surrounding tissue breaking down when the whole dose arrives at once. Splitting it into three or five sessions lets healthy tissue repair between them and gives up a little of the biological punch in exchange. Cavities after surgery often go the same way, since a cavity outsizes the lesion removed from it.

Risks and side effects

Side effects from radiosurgery arrive on a schedule, and knowing the schedule is most of what makes them bearable. Very little happens on the day. The problems that do come tend to arrive in three separate waves, weeks and then months apart, and each wave has its own explanation and its own answer.

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The one to understand before you consent

Radiation necrosis counts as the complication particular to this treatment, and it appears between six and twelve months afterward, late enough that people have stopped expecting it. Tissue inside the treated volume breaks down, swells, and produces headaches or the return of whatever symptom the lesion originally caused. On a scan it can look almost exactly like the tumor growing again, which is the source of a great deal of fear, and telling the two apart sometimes needs perfusion imaging, sometimes a follow up scan two months later, and occasionally a biopsy. Most cases settle with steroids. Risk rises with the treated volume and with the dose, which is one of the reasons larger lesions get their dose split across several sessions. The timing catches people out. A patient who has felt well for the best part of a year, whose scans have been quiet, who has started to think of the brain as the settled part of their illness, develops a headache and finds themselves back in a scanner being told that something has appeared at the treated site. Knowing in advance that this window exists, and that the first assumption is inflammation and the second is regrowth, takes a good deal of the terror out of that appointment.

Follow up, and the scans that confuse people

Scans after radiosurgery need reading against each other, and a single image on its own is close to meaningless in the first six months, so the pattern below stands as the usual one for brain metastases and your oncologist will tighten or loosen it depending on what the rest of your disease is doing.

Expect the treated lesion to get slightly bigger before it gets smaller, on more scans than you would like. Shrinkage over months is the normal course, disappearance is not the usual outcome, and a stable scar on imaging years later counts as success and not as failure.

What radiosurgery does not do

Radiosurgery removes nothing. A treated lesion normally stays visible on scans for years, and the goal is a target that stops growing instead of a scan that goes clean. Patients who expect erasure spend the following year reading their own reports as failures.

The limits worth knowing in advance

Mass effect comes first. A large lesion pressing on the brain and causing symptoms right now needs that pressure relieved, and radiosurgery cannot relieve pressure quickly, which is why an operation comes first in that situation and radiosurgery follows. Radiosurgery also treats what can be seen and nothing else, so disease scattered microscopically through the brain is outside its reach by definition. Arteriovenous malformations take two to three years to close and go on bleeding during that wait. And the treatment does nothing whatever for cancer elsewhere in the body, which is managed by the oncologist who sent you and continues alongside. None of that makes radiosurgery a weak treatment. It makes radiosurgery a precise one, with a defined job, and the mistake patients are pushed toward by the internet is treating it as a gentler substitute for every option on the table, which leads them to argue for radiosurgery in exactly the situations where an operation or a whole organ treatment would have served them better. A lesion that needs an operation needs an operation. A brain full of disease that no scanner can resolve needs a treatment that reaches the whole organ. Radiosurgery earns its place by doing one thing extremely well, and the consultation that matters is the one where somebody works out whether your case is that one thing.

Cost, coordination and having radiosurgery in Istanbul

No price appears on this page, because a number written today would be wrong by the time you read it. What we can describe is where the money goes and how a remote assessment works, and for this treatment the assessment is the part that decides whether traveling makes any sense at all.

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The international patients office covers English, Arabic, French, Russian, Serbian, Romanian and Spanish, and interpreting for other languages is arranged before arrival. One coordinator stays with you from the first message until you leave and remains reachable on WhatsApp afterward, which matters when a scan at month nine raises a question. Rooms include a companion bed where an admission is needed, accommodation and transfers are arranged around the treatment dates, a female physician is available on request, an invitation letter for the visa goes out around ten days ahead, halal and vegetarian and diabetic meals are routine, and a prayer room is open on site.

Plan on around two weeks in the country for a single session treatment, since planning runs one to two weeks after the mask is made. Back home the follow up scans carry on locally, with the images sent to us for review at agreed intervals, and your oncologist receives the dose report and the treated volumes so that anybody reading a future scan knows exactly what was irradiated and to what level. That last document is the one people underestimate. Nine months later, when a radiologist who has never met you is deciding whether a bright area on an MRI is necrosis or recurrence, the difference between a useful answer and a guess is whether they can see the isodose lines laid over your anatomy.

Send the MRI and ask us the fourth question on the list above.

Radiosurgery FAQ

Most first messages from abroad open with the questions below.