Canada’s National Meson Facility
Technology Transfer Bulletin
CANCER TREATMENT AT TRIUMF
For the past 4 years, TRIUMF has been the site of Canada’s only proton therapy unit that treats cancerous growths within the eye,
called ocular melanomas. There are about a dozen other similar facilities worldwide, and the cancer treatment program at TRIUMF
was made possible through a collaboration between the BC Cancer Agency, the University of British Columbia’s Eye Care Centre
and TRIUMF. The Mr. & Mrs. P.A. Woodward’s Foundation provided funds to construct the patient treatment chair and the proton
beam line equipment.
Before proton treatment became available at TRIUMF, the usual course of action for Canadian patients with large tumours or ones
at the back of the eye near the optic nerve was to remove the eye entirely. For smaller tumours, the preferred treatment is still
to implant a radioactive disk for a few days. Occasionally it is possible to remove small tumours surgically, but this can be
difficult. Any of these alternatives could damage other sensitive parts of the eye and result in some loss of vision. Proton therapy
offers the possibility of having the tumours stabilized, the eyes preserved, and depending on the
patient, the vision intact.
Normal cells in the body divide and form new cells in an orderly and controlled manner throughout life
to replace worn out tissue, heal wounds and maintain healthy organs. When cells grow out of control,
they can form a mass known as a tumour. Benign tumours are those that grow and enlarge only at
the site where they begin. They do not spread to other parts of the body. Malignant tumours (cancer),
on the other hand, not only enlarge locally but also tend to invade and damage the nearby tissue and
organs, and spread to other parts of the body. This is called metastasis.
An ocular melanoma is a malignant tumour originating in the pigment-forming cells of the eye. The most common site is the
choroid layer, which is located between the sclera (white fibrous tissue of the outside of the eye) and retina (innermost layer).
Hence, the proper name is Choroidal or Uveal Melanoma. The outlook for local cure depends strongly on the size and growth
rate of the tumour. The 5-year local control rate (where the tumour is sterilized and incapable of further growth) is 95%, and the
5-year survival expectation is approximately 80%,
irrespective of the type of treatment received.
The Equipment and Treatment
Before treatment, a surgeon attaches three or four very small
metal disks to the eyeball, around the edges of the tumour.
These make the tumour edges visible in an X-ray picture
(taken just before the treatment, when the patient is already
positioned in the chair). This allows exact alignment of the
proton beam. The treatment team (a radiation oncologist, a
physicist and an ophthalmologist) calculates the best angle
of entry of the proton beam, to ensure maximum damage to
the tumour and minimum damage to the optic nerve and the
lens of the eye. The patient’s head is held still with a mask
and a bite block, both custom made. However, the eye itself
is not immobilized. To help the patient, the room lights are
turned off and the patient is asked to stare at a small flashing
light, which is positioned so that the protons enter the eye from the planned direction. The eye position is monitored using a TV
camera with large magnification. If motion is detected, the operator can quickly turn off the beam.
Following the development of a treatment plan, technicians test the treatment system to make sure that everything works properly.
The patient is now ready for treatment. He/she is aligned each day using the X-rays, and the proton beam is turned on for about
2 minutes. After four daily treatments, the tumour is incapable of further growth and will slowly regress.
TRIUMF’s main cyclotron can accelerate protons to speeds up to 3/4 the velocity of light and up to energies of 520 MeV. Proton
therapy, however, requires a slower-moving beam of protons to penetrate the depth of the eye. The optimum beam energy for eye
melanomas is found to be between 70 and 75 MeV.
Why Protons instead of Other Radiation?
Radiotherapy has been used for many years, but most of the treatments have been done with
X-rays (photons). X-rays are successful in destroying tumours but they also destroy healthy
tissue around the tumour. This is because the penetrating power of X-rays decreases
exponentially with increasing depth. This means that X-rays deposit most of their energy near
the surface of the body. If the tumour is deep-seated, this presents a problem.
Protons are particles that form part of the nucleus of every atom. Being particles, they are able
to slow down much faster than X-rays. Their power, however, does not decrease exponentially
like X-rays. Instead, they deposit more energy as they slow down, culminating in a peak. The
depth at which the peak occurs can be controlled by the amount of energy the protons are given
by the accelerator. They are also massive enough to stay on their directed path as they
penetrate into the eye, without being scattered into surrounding tissue. The proton beam can
be “modulated” so that it contains protons with a range of velocities. This means they will
deposit their tumour-destroying (kinetic) energy at different depths inside the tumour, since the
faster protons will penetrate a little deeper. Thus the entire tumour gets a uniform dose of
radiation, with a sharp fall-off at the edges and at the “downstream” end, and is sterilized with
minimal damage to other nearby parts of the eye.
Since 1977, proton
therapy has been used
successfully in other
countries. It is well
tested, and is the
preferred treatment for
medium sized tumours.
The first ever treatment
that was performed at
TRIUMF occurred in
August, 1995. Since
then, we have treated 50
patients. Before this,
Canadian patients had to
go abroad for proton
treatment. Now they can
receive it here at home,
and at a much lower cost.
TRIUMF hosts and organizes a number of conferences every year, usually between the Spring and Fall seasons. They are all
scientific or technical in nature but range from undergraduate to post-doctoral levels. Participants at these conferences come from
all over the world and the number of attendees range from 15 to over 1200 per conference. The number of attendee days for the
past year totalled 7724. It is through these conferences that TRIUMF has another impact on the economy of British Columbia,
and allows for one-on-one exchange of the latest ideas with scientists from around the globe, furthering the quality of Canadian
research as a whole.
On May 28, TRIUMF was pleased to host the French Ambassador from Ottawa, Mr. Denis Beauchard. He was accompanied by
the French Consul, Mr. Dejaeger and the French Scientific Attaché, Mr. Blamengin, both from Vancouver.
Mr. Ross Fitzpatrick, a B.C. federal Senator, accompanied by Ms. Pam McDonald from the Prime Minister’s Office and Ms.
Audrey Sojonky from B.C. minister, Mr. David Anderson’s office, also visited TRIUMF.
A NOTE OF THANKS
TJM Technical Centre, the research arm of MacMillan Bloedel, has recently donated various microwave equipment to TRIUMF.
TRIUMF staff have been working with TJM staff for many years, providing them with solutions to electronic and microwave issues.
We would like to take this opportunity to thank TJM for their generous contribution.
Technology Transfer at TRIUMF is funded by NRC and NSERC.
Technology Transfer Contacts: Philip L. Gardner Division Head, Technology Transfer, (604) 222-7436,
Ann W. Fong
Questions and comments regarding this newsletter can be addressed to either of the above.
Technology Transfer Officer, (604) 222-7471, email@example.com
For information on how to become part of TRIUMF’s supplier base please contact Andy Decsenyi, (604) 222-7416,
TRIUMF is operated as a joint venture of: Associate Members: TRIUMF
University of British Columbia University of Manitoba Carleton University 4004 Wesbrook
University of Victoria Université de Montréal Queen’s University Vancouver, BC
Simon Fraser University University of Regina V6T 2A3
University of Alberta University of Toronto Canada