A ray of light for cancer treatment

Cancer can be deadly and the treatments to combat this disease often have undesirable side-effects.

For example, X-rays to detect tumours and radiation therapy to destroy malignant tumours employ potentially harmful ionizing radiation. And chemotherapy, another treatment method, for killing cancerous cells uses toxic substances.

New research has shown that a ray of light - channeled through optical fibres - may offer safer and more effective ways of testing for and treating some cancerous tumours.

Currently, scientists at the Canadian Institute for Photonics Innovation (CIPI) Network of Centres of Excellence are experimenting with fibre optics to fight cancer.

One application being studied is the use of optical methods for screening women at risk of developing breast cancer. Another application being examined is using lasers and photosensitive drugs to combat cancerous tumours.

Using optical methods to detect women at risk of developing breast cancer:

Scientists at CIPI are the first to experiment with safer optical methods for identifying women at risk of developing breast cancer, which will help doctors determine who should have a mammogram.

Laser in laboratory at the University of Sherbrooke

Deciding who should receive a mammogram poses a dilemma for doctors. Screening all women this way costs too much. Nor is it completely safe. Mammography is potentially harmful since it employs X-rays, a type of ionized radiation.

For these reasons, doctors tend to limit mammograms to women in known risk groups. "But who do you test? Everyone who is over a certain age? Everyone who has a family history? Everyone who is overweight?" queries Dr. Brian Wilson, a researcher with CIPI at the Ontario Cancer Institute at the Princess Margaret Hospital in Toronto.

This uncertainty can result in doctors failing to recommend mammograms to women who need them.

But optical methods for predicting women at risk of developing breast cancer may help remove the guess work.

"Screening with an optical method is significantly cheaper than mammography and it is also safer since it uses light instead of X-rays," Dr. Wilson explains.

The optical method works by measuring the spectrum of light transmitted through the breast.

"Changes in breast tissue density is a high indicator of risk," Dr. Wilson explains. "These changes can be identified by abnormal transmission of light through the breast in the red and near infrared spectrum."

According to Dr. Mike Patterson, a CIPI researcher at the Hamilton Regional Cancer Centre, the optical method of screening involves shining a white light channeled through an optical fibre bundle on the breast. Another bundle of fibres collects the light transmitted through the breast tissue and delivers it to a spectrograph. The spectrograph splits the light into its component colours and measures the light that passed through the breast in the red and near infrared spectrum.

Optical methods are being studied to predict women at risk of developing breast cancer, not as a replacement for mammograms, which detect breast cancer.

"Actually detecting small tumours is very difficult with optical methods since the breast tissue absorbs and scatters light," Dr. Patterson explains.

Using Lasers and photosensitive drugs to kill cancerous tumours:

Photosensitive drugs triggered by light have been employed to fight cancerous tumours for more than two decades.

The treatment is known as Photodynamic Therapy (PDT). To date, all medical applications of PDT are based on single photon absorption. But it is possible to produce different, and potentially more powerful, photochemical reactions in photosensitive drugs by using two or more photons.

Scientists at CIPI are the first to conduct research on two-photon PDT using infrared light instead of ultraviolet light. "Infrared light is safer than UV light since it can migrate deeper into the tissue, unlike UV light, which is absorbed by the first layers of skin, resulting in damage," explains Dr. Dan Houde a CIPI researcher at the Université de Sherbrooke.

According to Dr. Paterson, PDT involves giving a patient a non-toxic photosensitive drug. Using optical fibres doctors can direct light onto any accessible surface inside the body and activate the photosensitive drug with light from a laser.

"Typically, PDT is used on skin, mouth, throat, lung, intestinal and bladder cancers," Dr. Patterson says.

PDT can also be used to kill any remaining cancerous cells after surgery to remove tumours.

PDT is less harmful than chemotherapy since it can target cancerous cells directly. In contrast, patients undergoing chemotherapy are given toxins that are intended to kill cancerous cells, but also damage normal cells.

Normally, for one photon PDT to initiate a reaction to cause a photosensitive drug to destroy a tumour, oxygen must be present.

But tumours often lack oxygen since they grow so fast.

Two photon PDT, however, has been shown to push the photosensitive drug to a higher excited state, that can destroy cancerous cells even without oxygen.

"Currently, we are testing two photon PDT on molecules," Dr. Houde says. "We anticipate experimenting on actual cells in the fall."

For more information please visit the Canadian Institute for Photonic Innovations Web site.

by Michael Rappaport