Proton Therapy
The American Cancer Society currently estimates that approximately 1,400,000 Americans are being newly diagnosed with cancer each year. Fifty Percent (700,000) will receive traditional radiation therapy as part of their cancer treatment while the remainder will either be considered "untreatable" or their prescribed treatment will fail.
The costs of cancer continue to soar. For the year 2006, the National Institutes of Health estimated the total direct and indirect costs of cancer to be $263.2 billion, up from $180.2 billion in 2001. These costs include direct medical care, loss of productivity during the illness and loss of productivity due to premature death. These statistics prove there is a great need to improve the treatment of solid tumor cancers, both in the curative rate and in reduction of peripheral side effects. We believe that one of the solutions that can improve mortality rates and quality of patient care is proton beam therapy.
Proton therapy is the most technologically advanced method of treating solid, non-metastasized tumors. Many radiation oncologists and medical physicists believe that proton therapy represents the ideal treatment for solid tumors because the physics of proton therapy suggest that it can more effectively control localized cancer while decreasing treatment related side effects and morbidity. Unlike conventional radiation therapy, and even image guided radiation therapy, proton therapy can deliver a highly precise and direct dose of radiation energy to the target tissue (tumor) with minimal damage to the surrounding healthy tissue.
In many cases, it is the potential damage to healthy tissue that prevents cancer patients from receiving any radiation therapy at all, receiving only palliative care. The ability of proton therapy to maximize the delivery of radiation to the tumor allows radiation oncologists to prescribe doses at levels that could be potentially dangerous with conventional radiation therapy or IMRT.
The concept of employing proton therapy to treat cancer patients was first proposed in 1946 by Dr. Robert Wilson of Harvard University. The first patient was treated with this technology in 1955. In 1990, Loma Linda University Medical Center was the first institute to incorporate proton therapy into a medical facility dedicated to the treatment of cancer. It is estimated that the Loma Linda facility treats approximately 2,000 patients annually.
Protons exist in the nuclei of atoms and have electrons orbiting them. For proton therapy, physicists separate positively charged protons from hydrogen atoms by stripping off the negatively charged electrons. Powerful magnets bend the proton stream into a circular path and then control it as the stream is accelerated to near light speed inside either a cyclotron or its variable energy cousin, a synchrotron. The speed of the resulting beam and thus its energy is measured in electron volts. The higher the electron voltage, the heavier the punch is when the beam hits a tumor in the patient’s body. Achieving 250 million electron volts is the power requirement strength needed to reach tumors in all but the most obese patients.
When protons strike a tumor, they have about the same impact on the cancer cells as X-rays. The energy from both types of treatment disrupts bonds of molecules in the cell, leading to breaks in the DNA strands of cell nuclei. If the cell cannot repair itself, it dies, or at least loses its ability to replicate. The difference in the tissue interaction effects of protons and X-rays lies in what takes place before and after radiation reaches the tumor. X-rays release much of their energy quickly after penetrating the skin, disrupting the molecules of healthy tissue and organs proximal to the tumor. Proton energies are selected so that the vast majority of their destructive energy gets deposited at a specific depth, known as the Bragg Peak, which can be precisely calculated as a function of the beam’s initial energy. The beam energies are chosen so that the highest radiation dose is concentrated within the target. Unlike X-rays, which pass completely through the body, protons go no farther than the tumor, sparing everything behind it. More energy reaches the cancerous cells, so more damage is wrought by each burst of energy. Side effects caused by the irradiation of normal tissue in front of and behind the tumor are, while not completely eliminated, greatly reduced. |
