What are protons?
Protons are positively charged particles – the nucleus of
the hydrogen atom. In radiotherapy they enter the human body at
a pre-selected energy level and continue in a straight line up to
a precisely calculated depth. While moving, they release energy
with little radiation damage effects. Toward the end of their trajectory
they slow down, coming to rest at the Bragg peak (called after the
physicist of that name), where they release most of their energy
and damage the cells. Behind the Bragg peak the dose reduces to
nil after a few millimeters. This physical profile is the reason
for using protons in radiotherapy. It permits deep-seated tumors
to be treated without overshooting the mark.
How does proton
Proton radiotherapy works by ionizing tissue molecules, which damages
the cell nucleus, the surrounding membrane and other components,
and thereby inhibits cell growth. Cell division is interrupted or
the cell dies.
In comparison with the photons used in conventional radiotherapy,
protons have certain physical advantages. They release their maximum
dose – which attacks the tumor cells – right at the
end of their trajectory. The point where they stop is called the
Bragg peak. Their speed (or energy) is calculated so that this point
occurs at a precisely selected spot within the tumor. No radiation
is deposited in the healthy tissue behind the tumor. The dose released
in healthy tissue on the way to the tumor is considerably less
than with photon therapy. Therefore, on the one hand the sparing
of healthy tissue is optimal, and on the other a significantly higher
radiation dose can be released precisely within the tumor.
can best be treated with proton therapy?
Proton therapy is best used where high dose to the tumor and maximum
precision is required. If the medical indications favor lower dose
and wide-area radiotherapy, proton treatment may bring no distinct
advantage. In case of doubt, a comparative therapy plan can be drawn
up, and a decision for proton or photon therapy made on the basis
of the calculated dose distributions.
What results has proton therapy achieved? What are the chances
of a cure?
Protons have been used in medical therapy since 1954, when patients
were first irradiated with these positively charged particles in
Berkeley, California. Since then more than 70'000 people have been
treated at various centers worldwide, mostly for tumors of the
eye (choroidal melanomas), brain, skull base, spine and pelvis.
Impressive success has been achieved with eye tumors, with a local
tumor control rate exceeding 98% after five years, and there has
been a similarly striking increase from 40% to more than 80% in
the control rate for chondrosarcomas and more than 65% for chordomas
of the skull base. These results reinforce the thesis that precise
placing of the radiation dose, along with the significantly higher
radiation that can thereby be released inside the tumor, enable
growth to be halted in even relatively radiation-resistant tumors,
or permit them to be destroyed altogether, without damage to surrounding
It is on the basis of these successes that the spot-scanning technique
and compact gantry at PSI have been developed and built. Other countries
(Japan and the USA in particular) have developed similar proton
therapy facilities for treating tumors in all regions of the body.
As facilities spread for treating tumors that cannot be adequately
subjected to conventional radiotherapy, we may expect from all these
sources an increase in the indications for proton-beam treatment.
The PSI spot scanning technique, with its great advantages in precision,
nevertheless remains unique worldwide. Other centers are considering
to implement similar scanning technologies as the PSI scanning technique for their facility.
What are the
Side effects are divided into acute and long-term effects. They
depend both on the condition of the organs concerned and on the
radiation dose to which they are exposed. Radiation has its effects
where the dose is deposited. For example, hair loss will only occur
when the skull is irradiated, and temporary inflammation and discomfort
will generally arise after radiotherapy affecting the mucous membrane
of the bladder or rectum, but as a rule this lasts only a few weeks.
If you need radiotherapy, you will be informed in detail about possible
side-effects. As protons generally release little radiation in healthy
tissue, side effects are minimal and can be treated. Acute effects
occur during or immediately after treatment and generally last only
a few weeks. Long-term effects can occur months or even years after
treatment has ended, and are frequently permanent. They then as
a rule need regular treatment and may seriously affect a patient's
overall well being. For this reason great trouble is taken when planning
a therapy to avoid radiation of healthy organs – nerves, skin,
brain tissue etc. Protons are ideally suited to this task, and the
rate of long-term complications after proton therapy is low.
Will I feel anything
during the therapy?
Proton therapy is painless and does not burn. Patients feel nothing
during treatment. There are rare situations when specific sensory
centers in the brain are irradiated, which can lead to temporary
stimulation during treatment, causing e.g. light flashes or scent
How long does
the therapy last?
A course of radiotherapy usually lasts several weeks, with a relatively
large number of small individual doses given, until the total dose
necessary to destroy the tumor is reached. As a rule this takes
25-37 days of treatment. At PSI we currently calculate 5 days
of treatment per week, so a course of therapy lasts from 5 to 8
weeks. On each treatment day the therapy lasts about half an hour,
most of which time is taken up with the exact positioning of the
body so that the tumor can be irradiated with high precision, optimally spearing
out the surrounding tissue. The proton irradiation itself only lasts
a few minutes.
Where do patients
stay during the therapy?
Proton therapy is predominantly an out-patient treatment worldwide.
Our patients either live within one-and-a-half hours' drive from
PSI, or they rent a room or apartment nearby for the duration of
the treatment. We have contact addresses and can help arrange accommodation.
We insist that patients be accompanied by a relative or friend,
and if this is impossible they will stay in a local hospital in
Canton Aargau. This may also be necessary for medical reasons, for
example if the patient is at the same time undergoing chemotherapy.
Other hospitals may be called on in specific instances – e.g.
for treating small children under anesthesia.
How do patients
arrange treatment at PSI?
As a rule patients are referred by their specialist clinic or physician,
but in a number of cases relatives, friends or the patient themselves
make the initial contact. We always take time to discuss the patient's
individual situation, and if proton therapy is indicated, the treatment
will take place in consultation with the patient's own doctors.
on cases where proton therapy offers major advantages in comparison
with conventional radiotherapy, or where it is the only possible
method of treatment.
What does proton
Proton therapy is still considerably more expensive than conventional
radiotherapy, but with further industrial developments and the gradual spread of this technology worldwide, the costs could come down and approach those of
modern photon therapy. And as both short and long-term side-effects
are lower for many of the treatments with protons, overall costs could come even lower than with conventional radiation therapy.
So, proton therapy has the potential to reduce health provision costs,
but this has to be demonstrated and established in practice.
Are the costs
of treatment accepted by health insurance organizations?
Since January 1, 2002, reimbursement of proton therapy costs for
the following tumor types has been mandatory for Swiss health insurance
• meningiomas (benign and malignant),
• low-grade gliomas (grade 1 and 2),
• cranial tumors and those in the ear, nose and throat area (ORL tumors)
• tumors in the base of the skull and in ORL area
• chondrosarcomas and sarcomas
• pediatric tumors
• inter-ocular melanomas
How do I contact PSI and obtain information?
Contact the secretaries' office at PSI's Center of Proton Therapy:
Tel. +41 (0)56 310 3524
Fax +41 (0)56 310 3515