Proton therapy is
based on about fifty years extensive and positive experience of
the effect of proton beams on diseased and healthy cells in the
body. To date, about 80,000 patients have been treated with protons
at more than 35 centers world-wide, predominantly those with eye
tumors, brain tumors, or tumors in the area of the head and
neck and pelvis. This broad clinical experience has shown very
clearly that, compared to photon therapy, it is the spatial precision
in applying the radiation, which is of decisive importance. This
provided the motivation for PSI specialists to develop a new proton
therapy facility for high-precision irradiation of deep-seated
tumors. The PSI gantry has been in operation since 1996 and by
end of 2011, more than 800 patients had been treated with protons.
Melanomas
of the eye
In 1984 the first treatments with protons of eye tumors in Western
Europe were carried out at PSI. By end of 2011 we had treated
more than 5700 malignant eye tumors with the OPTIS proton therapy
facility. The therapy success rate includes more than 98% of the primary
tumors being cured and in 90% of the cases the eye could be saved.
Spot-Scanning
for deep-seated tumors
The success rate of the eye treatments and the good experience
with proton therapy for other indications at the Harvard Cyclotron Laboratory in Boston
provided the motivation for the PSI specialists to develop a new
proton therapy technique for high precision radiation of deep-seated
tumors. For this installation a pencil beam of protons is computer controlled
in such a way that high dose spots of protons can be positioned
very precisely, for an exactly specified period of time and at
any desired location within the tumor. By superimposing many different
spots - about 10,000 within a volume of one liter - the radiation
dose can be distributed uniformly over the entire tumor. This
is the principle of the Spot-Scanning
Technique implemented into the PSI-Gantry.
Meningiomas
About 50 patients were suffering from meningiomas. These tumors
arise from the coverings of the brain (the meninges) which are
located between the bones of the skull and the surface of the
brain. They grow slowly, displacing adjacent structures, and may
infiltrate the surrounding cranial bone. Depending on location
and size, they may cause severe headaches, epileptic attacks,
disorders of brain function, episodes of loss of consciousness,
paralyses and other neurological defects. If surgical removal
is impossible, the precise spatial adjustment of the radiation
dose involved in proton therapy offers particular benefits.
Brain tumors
More than 50 treatments have been carried out for patients with brain
tumors (for example: gliomas, ependymome, medulloblastome). Most
such tumors arise from glial cells, the supporting cells of the
brain tissue, and the more closely they resemble the cells from
which they originate, the more likely they are to respond well
to treatment. In these cases we refer to tumors as grade 1 and
2. When the tumor cells have developed differently to the original
cells, so called (entdifferenziert) then proton therapy cannot
promise more than photon radiation as the whole brain must be
evenly treated. These grade 3 and 4 tumors and glioblastomas
are not part of the treatment program at PSI. These tumors
are usually treated in clinics with a combination of chemo- and
radiation therapy.
Chondrosarcomas and Chordomas
More than 400 patients were referred for proton therapy
because of chondrosarcomas or chordomas involving the base of
the skull or the spinal axis. Such tumors are of connective tissue
origin, grow slowly and very seldom metastasis, but destroy the
most susceptible adjacent structures, often those which are essential
for life. The cranial nerves are located at the base of the skull,
the optic nerves are close by, as also is the optic chiasm. Permanent
damage to these structures is likely to cause blindness. The brainstem,
as a part of the central nervous -system, cannot tolerate persistent
pressure from a tumor, far less actual invasion, but it also
has limited tolerance towards irradiation.
Because the proton beams stop at a calculable depth, depositing
most of their radiation load within this stopping region (the
Bragg peak), chordomas and chondrosarcomas of the skull base have
for many years been treated by irradiation. This has become the
subject of a well organized clinical trial conducted mainly with
the Harvard cyclotron at Massachusetts General Hospital in Boston.
Convincing success has been achieved: for chondrosarcomas local
tumor control has been raised from about 40% to over 80%, while
for chordomas it is now about 65%. These tumors, like melanomas
of the eye, have therefore become an indisputable indication for
proton therapy. We have achieved successful tumor control for
our patients, together with general well-being and a highly satisfactory
quality of life.
Sarcomas
Sarcomas – malignant tumors arising from the connective
and supporting tissues – also occur in other parts of the
human body, for example, in the coccyx, in the lumbar vertebral
column, on or within bones and joints and also in muscle tissue.
Up until middle of 2011 we treated more than 120 patients, with sarcomas
not in the spinal or scull base area. Some of these treatments
were in partial combination with surgery and or chemotherapy and
appear to be successful so far.
Prostate Cancer
Up until the end of 2003, we treated 13 cases of prostate cancers
with protons. These treatments were likewise successful, and the
patients are doing well. From 2004 on there was
not the capacity to treat any prostate cancer patients and the health insurance system in Switzerland is not covering the costs for prostate cancer treatment with protons.
ORL tumors
Tumors in the ear, nose and throat region (ORL tumors) often
grow in close proximity to the sensitive structures of the brain,
the base of the skull or the spinal column. Up to 2011,
we had treated more than 40 ORL tumors (including two skin tumors), in
partial combination with surgery, chemotherapy and, in some cases,
also with conventional radiation.
Children and youth
Until end of 2011 we treated more than 200 children and youth
between the ages of one and twenty-years old. More about 150
of these, between the age of 1 and 5, had to be treated under
anesthesia, in order that they remained absolutely still during
the treatment. The tumors were located in the scull or the base
of the scull and between 14.0 and 74.0 CGE was applied. In some
cases this was also in combination with conventional photon radiation
treatment.
Age distribution
of patients
More than 50 % of patients were under 40 years of age, while more
than 30% were children and young people under 20. Such patients
derive particular benefit from proton therapy, because the precise
delivery of the highest radiation dose within the tumor minimizes
damage to the vulnerable and still growing body of the child or
young person. It also means that subsequent, secondary tumors
are less likely to arise than after photon therapy.
Intensity-modulated proton therapy (IMPT)
PSI operates world's only facility able to treat patients with intensity-modulated radiation therapy
with protons (IMPT). First patient treated with IMPT was a
young male patient, suffering from a chondrosarcoma of the
upper thoracic spine in 1999. Once again, our objective was to control
the tumor, while giving the best possible protection to the immediately
adjacent spinal cord, so as to preserve the working capacity and
quality of life of this 36 year-old man. Seven years after the conclusion
of the therapy, he is free of symptoms and working full time.
We have further developed this technique,
and in the past years more than 50 % of the patients were treated fully or partialy with
IMPT.
Prospects for
curing tumors with proton therapy
In over 80% of the cases treated we have been able to
stop the growth and kill the tumor, curing the patient. The remainder
of the patients had such an advanced tumor growth or it was metastasized
so that despite the tumor being controlled the patient was not
cured. However in many cases an alleviation of suffering was achieved,
and treatment also slowed advancement of the disease. This was
achieved with nearly no side effects. Unfortunately, in some cases
the tumors grew again.
Clinical experience
– future developments
The
clinical results achieved so far seem to reliably indicate that
the developments in proton radiation techniques can offer patients
with certain cancer indications considerable benefits in therapy
and healing. Under the project
PROSCAN the facility is being continously expanded and by the end of 2012
we will be able to treat about 200 to 300 patients with
deep seated tumors on a year-round basis. Due to the technical
capabilities of the new Gantry 2, moving tumors will also be treated with the high precision scanning treatment technique at PSI. An additional treatment room (Gantry 3), which will have similar features as Gantry 2, will be installed beginning of 2013 and used for clinical research from 2016 on.
