The situation reads like the scenario for a science fiction movie. The enemy is an alien intruder that invades the human body, with deadly consequences. This enemy comes in many different forms and assumes a bewildering assortment of odd shapes, which can change when it is under attack. In their search for weapons with which to fight back, humans have developed an amazing technology — one that can seek out and identify the enemy as it hides within its intended victim; track and target its location, adjusting to any changes of shape or position; and destroy the invader with an intense beam of radiation that does minimal harm to the host body. The bad news about this scenario is that the enemy described is an all too real disease — cancer — the second-leading cause of death in the United States (after heart disease) and the slayer of millions worldwide every year. The good news is that the weapon described is real, too. It is a technology called Intensity Modulated Radiation Therapy (IMRT) and it is offering many cancer patients perhaps their best hope ever for successful treatment.

A Woman Named Sarah
Take a look at what happens in the hypothetical case of a woman whose name, let’s say, is Sarah. She is 42 years old, is married, and has two daughters, ages 12 and 10. She has gone to her primary care physician complaining of a nagging cough and occasional shortness of breath. She appears to be in good health otherwise, exercises regularly, watches her weight, and has never smoked. Nonetheless, chest X rays and follow-up tests confirm that she has lung cancer, the leading cause of death among the known forms of cancer, claiming more victims in the U.S. than breast, prostate, ovarian, and colon cancer combined. She is among the nearly one out of every five victims of lung cancer who neither smoke nor live with a smoker. What’s worse, the tumor has been classified as a type that, because of its size and general location, is inoperable using conventional pulmonary surgery.
      Other medical conditions make chemotherapy problematic. Like more than half of all the other cancer patients who are treated in the United States, Sarah is advised to undergo radiation therapy, also known as radiotherapy. As recently as five years ago, Sarah’s lung cancer would probably have been untreatable with radiotherapy because large doses of high-energy X rays, much like the chemicals used in chemotherapy, inflicted extensive collateral damage to surrounding healthy tissue. To minimize the effects of collateral damage, oncologists often had to limit the treatment dosages, which in turn cut down on the effectiveness of the therapy. This drawback would have been particularly acute in Sarah’s case, because lung tissue is especially sensitive to radiation damage and lung tumors are highly resistant to radiation treatment.
      Fortunately, Sarah has a new treatment option that has only recently become available. She can be treated at one of about 200 radiation oncology clinics around the world now using new SmartBeam™ IMRT technology developed by Varian Medical Systems. SmartBeam IMRT has been compared to shooting at a target with the precision of a high-powered laser. With IMRT, the target area covered by the X-ray beam is narrowed and matched to the shape of the tumor. This enables the oncology team to direct and narrowly concentrate potent doses of high-energy X rays at Sarah’s tumor while minimizing complications from hitting surrounding healthy tissue.
      With SmartBeam IMRT, Sarah’s oncology team will put her tumor in a crossfire, targeting it with precisely shaped beams delivered from several directions or angles. This will envelop the tumor in a finely sculpted radiation cloud within the area where the beams intersect.

The Preparation
Before beginning Sarah’s treatment, doctors will need digital high-resolution 3D images of her tumor and the surrounding anatomy. With sophisticated diagnostic imaging, the oncology team can establish the exact location and shape of Sarah’s tumor. This will make it possible to develop the treatment plan needed to deliver a high enough dose to eradicate the tumor without harming the surrounding tissue.
      To obtain the needed images, Sarah’s doctors may choose to use Computed Tomography (CT) in combination with Positron-Emission Tomography (PET). With CT scans, thin, low-energy X-ray beams are swept across a tumor-harboring area to generate a number of detailed cross-sectional images, or “slices.” For PET scans, patients are injected with glucose marked with a radiotracer such as fluorine-18, which emits positively charged electrons, or “positrons.” These positrons interact with surrounding tissues, producing photons that can be detected by the PET scanner. Since rapidly growing cancer cells metabolize glucose up to 20 times faster than healthy cells, the glucose concentrates at tumor sites. Cancer cells that have taken up the marked glucose appear on a PET image as a clearly visible bright spot.