Transcription
by Adam Valenti
Adjunct
Associate Professor Phillip Yuile
MB BS (Hons), FRANZCR, MA (Applied Ethics)
Director,
Radiation Oncology of Sydney
to
the Sydney Neuro-Oncology Group (www.snog.org.au)
Brain
tumour Support Group
at
the North Shore Private Hospital
Wednesday
16th May 2001
The
role of radiotherapy in the treatment of brain tumours
Please note that this is not Dr Yuile’s notes,
but audience notes.
What I want to do tonight is very briefly go through what radiotherapy
involves so particular family members know what the patient undergoing
radiation goes through and what the program is, and why the program exists, why
six weeks and not two weeks or ten weeks and so on.
There are many different sorts of brain tumours some are amenable
to radiation some are not particularly amenable to radiation. The most common brain tumours are the
astrocytomas then you get down to the more and unusual sort of tumours that one
can see. The malignant astrocytomas
basically come in four grades.
Grade 1 often occurs in children and they are often benign, we
operate and remove them and they have a very high cure rate. Then you get into grade 2 and 3 with grey
areas in the middle going through a grade four, which is a glioblastoma or grade
4; we call them GBMs. Many of you I am
sure would be agreeing with each terms they are regrettably the most common
brain tumour in western society and in the world and they are the most
aggressive. Sometimes someone might
start of with a grade 2 tumour and over a period of years that tumour would have
evolved and change into a grade 3 and often become a grade 4. Sometimes a grade 4 tumour just starts out of
the blue and we don’t know why, people look at mobile telephones, they look at
the airconditioners. There was a
Scandinavian study years ago that showed people with head injuries had a low
instance of brain tumours so we don’t really know what causes brain tumours.
Brain tumours are a bit more common in males than in females. They
are the 12th and 16th most common cancer in New South
Wales. So in the actual real numbers,
the numbers of people who get brain tumours are fairly small, about 5 to 8
people for 100,000 population. However,
they often occur in younger people in there prime of their working life and
their impact on society and their families can be more severe than many other
sorts of cancer.
Patients with brain tumours can present with headaches, weakness
or numbness down one side, difficulty in speech or confusion. Sometimes
forgetfulness or changes in behaviour may not be apparent to the family but
other people may notice them. It is in
retrospect that the wife or the husband would say she forgot my birthday before
Christmas but quite often when you are in the family situation you don’t notice
it.
There is a number of ways of treating brain tumours. These include surgery, radiation therapy or
chemotherapy. There is a type of radiation treatment called radio surgery or
stereotactic radiosurgery or gamma knife treatment that many of you would have
heard of or read of which is a very concise confined form of high dose
radiation. There is a new technique
now, which is largely a change on the external beam radiation but using
sophisticated computer modeling. This
is called Intensity Modulated Radiation Therapy (IMRT) and that’s starting to
become available throughout the world.
At the moment we don’t know whether it will change things in brain
tumours. Its exciting, things have
improved a lot in the last ten years, largely due to new computers, great
software, better imaging with MR’s, Pet Scan and so on, so we can see what we
are treating a lot easier.
The traditional treatment for brain tumours is to have an
operation. That operation might be a
biopsy, biopsy just means bits taken out and sent to pathology to be looked at
under the microscope and a name put on that tumour being a grade 3 astrocytoma
or grade 4 astrocytoma. Sometimes if it
can be undertaken, the biopsy is a bit more extensive and the surgeon will take
out more tissue. This is called
debulking, and if you are lucky and if it is in an area of the brain that can
be operated on successfully you may be able to remove the whole tumour with the
naked eye. Rarely can you get the whole
tumour out because tumours tend to have little roots that go out pass what the
surgeon can see. That is where the
radiation comes into and try and knock off or retard or dry up those little
roots that have gone out pass the naked eye.
Basically there is a rule of thumb, the more the surgeon can take
out the easier our job the better the outcome so if the tumour can not be
removed its better than being debulked and if its debulked its better than
being biopsied. It depends so much on
where the tumour is in the brain, how old the patient is, how fit they are,
whether they are right handed or left handed all these things come into it.
So the surgery is followed up with the radiation therapy and then
we wait for a while and see how that responds and then we have chemotherapy and
other drugs like thalidomide up our sleeves after the radiation.
That’s normally the structure: diagnosis, surgery, radiation and
then other treatment.
So what does radiotherapy involve? It involves meeting a
radiotherapist and you sit down and you have a talk about what’s been happening,
looking at the pathology, working out ways of tackling it and you have a
consultation or an initial assessment.
Then at another time, these things are not done at the same time,
patients come to the office and they say well I am here now can I have my
radiotherapy, it’s a bit like going to the surgeon saying I am here now can I
have my operation I’ve got five minutes to spare. These things, to be done properly, take time. They have to be booked, time has to be taken
over and hours have got to be spent to get the best result. So don’t expect to be treated and fixed on
day one. The first appointment is
followed by a planning time where we make a plastic mask and many of you would
have gone through the mask period.
The mask is very important because the mask is a thermal plastic
thing that you heat up, pop it over the patients head and it locks them onto
the machine and the reason for that is that it keeps the head in a very stable
position because that patient will be coming in every day for five days a week
for many weeks and you have to keep the same area every day. We don’t like moving targets, they
compromise results and they are dangerous so if we have the mask you can move
your arms and legs and every thing else but you can’t move your head so when
the lasers all lined up and the computer says fire, we're in business.
Making of the mask takes about an hour, you then have another CT
scan, because you have a CT Scan in the mask and you have it in the treating
position because we use that scan to plan the radiation in three dimensions so
it has to be very precise. Then you
need another scan in the mask after you have all the planning business done.
Then you go through a period called simulation where you are put
on a machine, which is like a fancy x-ray machine. That looks at all the angles
that we want to attack this thing, coming in from the left and the right and
behind and the front and where they all add up is where the target will be.
That takes about two hours so already we have spent about four hours and we
haven’t had a treatment yet. It's like
a pilot lodging the flight plan, if he does it quickly and goes to the wrong
place its not good for you so it is worth spending the time so when we do take
off we go to right places as safely as we can.
The planning time involves about four hours usually with a physicist and
technician working out the ways of getting the radiation beams into the bit we
want to zap.
Down the track we often re-plan we reduce the fields or the areas
being treated because each amount of tissue in the body can take a certain
amount of radiation safely, if we exceed that you damage that tissue. What we don’t want to do is damage normal
tissue but we don’t mind damaging cancerous tissue, so you will have a certain
amount of radiation in the big areas you can safely have and then the area will
be focused down and coming down to reduce down the treatment area. That is called re-planning. So somewhere along through the course of all
this you will probably have another set of x-rays and maybe another scan and be
re-planned.
The radiotherapy is five days a week, Monday to Friday. It takes about 15 minutes a day, though the
actual machine is only on for minutes or seconds. Patients often come back and say I counted up to 72 today when it
was only 71 yesterday, why the extra second?
The treatment itself does not take very long. The setting up and the
fiddling around to make sure its in the right spot takes the time. The course is in the order of six or seven
weeks. It normally runs five days a
week for 6 to 7 weeks, 32 to 33 doses, what we call batches, it is not
something that we can give in one shot.
It has to be lots of little bits and the boost often comes after the 4
to 5 week mark where we shrink down.
The side effects, you get tired particularly after major surgery,
the radiation takes as much out of you physically as the operation, so you have
had two major operations in a very short time.
You will have hair loss in the affected area which recovers variably, you
get a skin irritation where you are having the radiation the skin gets pink and
itchy after about the fourth week. We may give you cortisone treatment for the
redness and soreness. Depending on if
the ears are being treated you can get a built up of mucus, which we call glue
ear, and sometimes you need to see an ear nose and throat doctor and have the
tubes in the ears.
Sometimes down the track, years later, after radiotherapy, a 70
year old brain might be like a 75 year old brain. There are limitations to the areas of the brain we can safely
treat, like the brain stem, the pituitary, the optic chiasm where the nerves
cross over. They are very sensitive to radiation and you have to be very
careful. So the trick is to damage the
tumour without damaging the other structures.
Each part of the body can take certain amounts of radiation given over a
period of time. The brain, for example,
can take about 6000 to 7000 centigrays.
Once you get above that there can be damage the brain and so the trick
is to take the tumour up to as much as the high dose as you can without reaching
that threshold and causing damage.
The reason we give radiation each day is fairly complex but one of
the reasons is that it enables oxygen to get into the tumour, because radiation
needs oxygen to work if you gave it all in one big dose you just get a certain
amount. More radiation in one dose is
not better. Rather it is better smaller
doses over time as it causes less damage.
By giving lots of little doses we achieve a better result than giving
one big dose.
If you have a big hunk of cancer not all cells are in the same
place at all the one time. It might be 100,000 here 100,000 there so when you
have your burst of radiation you are only going to affect the ones that are
sensitive at time, its wasted on the other ones. By giving it daily all the other ones are moving around and
reproducing, your chopping them done its like soldiers coming out of a
trench. If you just fire all your shots
in one go you might knock out the first line but the others keep coming whereas
if you keep firing a bit, wait a bit, fire a bit, wait a bit you are getting
more soldiers. A given dose of
radiation kills a constant proportion of cells so by giving a little bit every
day we are chipping away at the tumour gradually and shrinking it down, we call
that fractures or daily doses.
Alot of people might say how do I know the radiation is
working? Can I have an x-ray to
check? I often say its like spraying
zero on a weed, you spray the zero, you come back the next day the weed is
still there, you come back the next day and the weed is still there it takes 4
days for the weed to go yellow and die.
The same with radiation. The
tumour is still there. It doesn’t just
suddenly go pop and disappear. Rather,
it gradually does shrink down and reduce down.
The next question is why can’t I have it Saturday and Sunday? You can’t have seven straight days of
radiation. People have tried it and you
get too much damage of the normal tissue.
Having a couple of days enables your normal tissue to regenerate and
recover. Some hospitals treat 9 days a fortnight, some treat 10 days a
fortnight. So you do need some time off
to enable your normal cells to regenerate and repair.
Radiosurgery or gamma knife, they are only suitable for very small
localised tumours usually 2cm or under and unfortunately most of the tumours
in the brain are bigger than that. It
has to be in a certain position you can access safely and it can’t be near
that optic chiasim. It can’t cross
the midline of the brain and it has to be in one spot. So stereotactic radiosurgery or gamma knife machines are only good
for a number of selected patients and in New South Wales each year there is
probably about 80 to 100 people to benefit from it.
One of the things with brain tumours is that you can treat a breast
cancer and no one will know you have had breast cancer, you can treat a lung
cancer or a rectal cancer, no one knows you’ve got cancer. Brain tumours are a bit different as they
affect the most complex computer known to mankind, the human brain, and one of
the problems is that’s why it is so difficult.
People can cope with a colostomy bag or a lump in the breast but when
someone’s behaviour or personality changes it becomes difficult for every one
that knows them and this is the ramifications for families, society, workplace,
everyone. One of the problems with the
brain is that it is a computer and if you’re a computer freak you know that you
can pull out the fan and the computer still works. Or you can pull out a part of the memory of the computer and it
still works but there are certain areas like the CPU that you can’t pull out
because the computer won’t work. The
same with the brain. There are certain
areas of the brain you can pull out and surgically you can remove, we can
affect with radiation and you can get away with being pretty normal but there
are some areas that you can’t touch and that’s the CPU of the brain.
The brain is far more complex than the breast or the rectum or the
lung and there are certain areas that you can get away with damaging and its
not a major issue but there are some areas that the patient can’t survive so we
are very limited in what we can treat.
There is a boost towards the end of radiation. That is, quite often we’ll give a large
volume of treatment, up to what we think is a safe amount, say at 5 weeks or
thereabouts. In the last week you may have another episode of this
re-simulation, you may have to go on the simulator again. While MR gives us the best picture of the
tumour, much better than a CAT Scan, we use CAT Scan to plan radiation
treatment. We can plan the radiation
based on the CAT scan because it picks real good densities. We use those densities such as air, fat,
water, blood, brain tissue. They all
have computer algorithms to work out the amount of radiation that gets
absorbed. The MR can’t do that because
doesn’t have those density readings. So
because the MR shows the tumour better than the CAT scan we can fuse the images
so we superimpose the MR on the CAT so we see the tumour on the MR but we use
the CAT scan in the planning. That is
why you have to have these scans.
Then the four hours or so with fiddling with angles comes into
place. The radiation therapists who are
science graduates, they do a special three year science program are the people
who set you up each day and line everything up and then they leave the room
because they don’t want to be radiated as they have to treat 40 or 50 people a
day. So they leave the room and you’re
in there by yourself listening to music if you wish for anything up to five to
ten minutes. You are usually only in there alone at one time for about a minute
or a minute and a half. Then they come
in again and the machine moves around, they check all the lasers and the
measurements, leave the room again, you’ve got another minute or a minute and a
half, then they come in and the whole thing is repeated. The whole session takes about 15 minutes,
there is a lot of physics involved, these machines have quite incredible
quality audits (QA) for safety reasons.
They have QA daily, weekly, monthly and quarterly and there is a physics
person along the side at all times.
During the course of radiation you will have x-rays taken. A lot of people say well is the tumour
getting smaller, is the x-ray good?
Those x-rays are not designed to look at the tumour because often there
is nothing to see, all those do is to confirm where we have been, if we are in
the right spot. Despite the mask some
people do wriggle, some people put on weight, particularly when they are
dexamethosone and their head is puffed up and you have to make another
mask. In that case all the measurements
change, so these things are double checked so that the amount of radiation
getting into that tumour is what we have calculated.
We are seeing people respond better and do better with treatment
and part of that is because they are having better surgery, part of that is
because there are better surgeons and better anaesthesia. Operations of 20 years ago took 5 or 6 hours
and people spent two weeks in hospital.
Now it's done in half that time and they are walking around a day later
and home a few days later and that is because of better anaesthesia, painkillers,
better operating microscopes and better trained surgeons. We now have better radiation because we have
bigger and better machines and better computer software so we can give more
radiation more safely.
Why doesn’t radiation work?
Sometimes tumours can be resistant and there are some tumours that we
treat that continue to grow despite what you do and we don’t understand
that. One of the things that the Sydney
Neuro Oncology Group (SNOG) is hoping to start, and we have applications into
the cancer council for grants, to look at comparing why some people respond and
others don’t on a genetic basis on the actual tumour and hopefully it will give
us some answers.
The size of the tumour: smaller tumours respond better than big tumours,
the more the surgeon can get out or debulk, the better our results would be
because we can only give that same amount of radiation. Whether you have a million cancer cells or
ten you can only have the same amount of radiation. The oxygen content of the tumour as we said we need oxygen for it
to work and a lot of these bigger tumours don’t have a good blood supply in
the centre, they are low on oxygen and radiation is not as effective. Some are very close to those areas we spoke
about, the optic chiasm or brainstem will only take 4500 centigrys of radiation,
you can’t give them 6500 because we damage it.
The tolerance of the patient, younger people tend to better than more
mature people and there is a bit of a cut off point with the age sometimes
and other factors we don’t understand.
I think the future is positive and optimistic but we still have a
long way to go.
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