Radiation therapy for cancer has been practiced for decades, but during most of the 20th century it was an imprecise science. Exposing malignant tumors to large doses of radiation was proven to be effective in killing cancer cells and shrinking or destroying tumors; however, normal cells and tissue would also be damaged in the tumor’s surrounding area.
Over the past quarter-century, improvements in medical research and computer technology have enabled oncologists to apply incredibly targeted doses of radiation to tumors for many types of cancer, resulting in improved outcomes for patients.
On this episode of Kentucky Health, host Dr. Wayne Tuckson speaks with an oncologist and professor at the University of Louisville to learn about the advances in radiation therapy, how radiation is applied to cancer patients, and what doctors and researchers are working on to make radiation treatment even more effective.
Dr. Shiao Woo, MD, FACR, is an endowed professor and chairman of the Department of Radiation Oncology at the University of Louisville’s James Graham Brown Cancer Center.
“I have always thought about surgery, radiation, and chemotherapy as the three branches of the military against cancer,” Woo says. “And radiation is really the Air Force.”
Improved Targeting Systems Revolutionize Treatment
Woo compares radiation therapy to the role the Air Force plays in military engagement because, like planes on bombing missions, radiation aims to destroy a distant target. He recalls World War II, where aircraft bombed a wide area in hopes of destroying a particular building or buildings but still caused much collateral damage. He contrasts that inexact approach to the current, satellite- and “smart bomb”-aided plan of aerial attack.
Starting about 25-30 years ago, Woo says, the same progress has been made in radiation. A medical instrument called the CyberKnife illustrates the modern technique.
The CyberKnife has a mobile robotic arm carrying a radiation gun, which is attached to a main workstation. There, coordinates derived from a preliminary CAT scan are entered in to a tracking system of sorts, and this system directs the mobile arm to move around the immobile patient and deliver radiation from multiple angles, at millimeter-level precision, largely avoiding harming nearby organs.
“Since we are able to greatly reduce the so-called side effects, or collateral damage, because of the CyberKnife, two things happen,” Woo says. “We can give a larger amount of radiation, and we can also reduce the number of treatments. …. We can now give quite large doses, doses we’ve never dared to use in the past.”
The CyberKnife, Woo explains, derives from a groundbreaking concept and instrument invented more than 60 years ago called the Gamma Knife, which is still occasionally used to treat cancer in the brain, head, and/or neck. It is also used to treat a painful condition known as trigeminal neuralgia that affects the primary nerve carrying sensation from the face to the brain.
In the Gamma Knife procedure, a helmet was placed on the patient’s head that had several open slots, through which pre-coordinated doses of radiation were beamed. Each individual dose traveled through the patient’s brain at precise angles to the target, or what Woo calls the “sweet spot,” where they all converged to strike the tumor.
The CyberKnife expands on the Gamma Knife instrument by employing the innovative, mobile robotic arm and sophisticated tracking system, enabling it to be used on the entire body. This way, the oncologist and his team can use an approach called intensity modulated radiation treatment (IMRT), which applies beams of radiation to specific parts of the tumor at varying angles and with different degrees of intensity. Woo says that IMRT is the preferred method of radiation therapy for cancers of the brain, head and neck, for many lung cancers, and for some cancers of the abdomen.
Recently, a procedure similar to CyberKnife was used in conjunction with immunotherapy to treat former President Jimmy Carter’s melanoma that had metastasized to his brain.
Making Radiation Therapy More Effective
“Radiation works in a couple of ways,” Woo says. “The most direct way is, irradiation destroys the DNA, which is the fundamental framework of any cell – it destroys the DNA, and the cell dies. But it works even more commonly in a second way. It changes the cell’s DNA but does not kill the cell immediately. So, when the tumor cell begins to divide, when the DNA has to split, that is when the cell dies.
“So, because of this, the tumor cells die in between the doses of radiation,” he continues. “Delivering radiation only takes a couple of minutes. And every day, there’s about 23-plus hours in between where nothing happens – but it does happen. In between.”
This “in-between” effect means that patients who have fast-growing cancers, such as lymphoma, may see improvement more quickly than those with slow-growing tumors that have less rapid cell division.
Today, Woo says that radiation is commonly used in conjunction with chemotherapy and, increasingly, with immunotherapy. He believes that the exciting new field of immunotherapy will make radiation even more effective due to its ability to “unmask” specific protein antigens in cancer tumors that shield them from the body’s immune system.
“We now increasingly realize that radiation, besides killing the tumor directly, has another benefit,” Woo says. “Which is, it exposes the antigen – a specific signal of the tumor – it exposes those signals so that your immune system can attack them.”
Woo acknowledges that radiation also has the capacity to kill immune cells and weaken the overall system, but he says that today, oncologists have adjusted their therapy and now avoid irradiating the lymph nodes near the cancer tumor, which enables white blood cells to continue their attack.
The most common side effect of modern radiation therapy, Woo says, is fatigue. This is brought about by the body’s reactions to chemicals that are released as dying cancer cells dissolve. Depending on the type of cancer, the release of these chemicals, called cytokines, can cause inflammation and muscle weakness and affect organs in various areas of the body.
When asked if we are winning the war on cancer, Woo offers a realistic, but hopeful, response that expresses one of the conundrums motivating current cancer research.
“Sometimes we do, sometimes we don’t,” he says. “The thing we have to remember, I think, is that cancer cells are incredibly clever. … And the only thing I have a problem understanding is that, all naturally occurring parasites – and cancer is a parasite – do not want to kill the host, because they’ll die with it. So, why does cancer do that? What signal could we learn to tell the cancer that we may be able to co-exist without killing each other?”
