Radiation can be a deadly force. It can be a powerful weapon against cancer but usually at the cost of healthy tissues — potentially causing long-term damage or even new cancers years later. After decades of improvements, researchers are working on developing even more precise methods to deliver radiation's lethal payload on target.
Alternatives to X-rays, called particle beam therapies, have the advantage of being "very targeted — they deliver most of their energy to the tumor, instead of healthy tissues," said Kazuo Hiramoto, corporate chief engineer of research and development at Hitachi Ltd. in Japan. However, this approach is very expensive, which has limited its availability to patients: "We have to continue to improve the technology and work to reduce the cost" to make these therapies more available, he said.
Top: How particle beam therapy works; Bottom: Kazuo Hiramoto | AAAS/Carla Schaffer
Hiramoto discussed his work on improved radiation therapies in the 2014 Annual Hitachi Lecture, which he delivered at AAAS headquarters on 4 December.
High-energy radiation damages cellular DNA, eventually killing the cell. Tumors lack the capability of repairing DNA that normal cells have, so as the damage accumulates, more tumor cells die than healthy cells. Radiation therapy is generally delivered in small doses over repeated visits, so that healthy tissue has time to repair while more and more tumor cells are killed.
Compared to X-rays, particle beam therapies deliver radiation with larger charged particles and heavy ions, such as protons and carbon ions. The larger particles have the advantage of losing less energy on their way to the tumor, and then depositing most of their energy at the target site. X-rays, by contrast, spread their energy along their path, including to cells beyond the tumor. The delivery of more energy from large ions also causes more DNA damage to the tumor cells.
Particle beam therapy was first used on patients in the United States in 1955. There are now about 80 particle beam facilities in operation or under construction worldwide, 21 of which have scanning capabilities, Hiramoto said. Fourteen of those facilities are in the United States. Only six carbon ion therapy facilities are operating — four in Japan, one in Germany and one in Italy. Hitachi began developing advanced proton beam therapy systems in the 1990s.
Hitachi's work on the technology led Hiramoto and his colleagues to work on refining a technique called "spot scanning" using proton beams. The method delivers short bursts of energy directed to an exact spot by magnets, allowing a technician to send different doses to various depths and spots within the tumor. It's especially useful for tumors with a complicated shape, or that are close to critical organs.
When combined with real-time tumor imaging or tracking, spot scanning could deliver very precise doses, even to moving tissues such as lungs, Hiramoto said. The first patients will receive spot scanning therapy with real-time tumor tracking using protons in Japan in the near future, Hiramoto said.
About 45% of American men and 33% of American women will develop cancer sometime in their life. About 65% of those diagnosed in the United States will be treated with radiation therapy, either alone or with chemotherapy or surgery.
Kazuo Hiramoto
Another area of research Hiramoto finds promising is using genetic analysis to determine which therapy would work best for a patient's particular tumor. While this approach is currently most commonly applied to determine the best chemotherapy techniques, it can also be used to determine the best particle radiation treatment, he said.
Imaging techniques such as computed tomography (CT) scans and magnetic resonance imaging (MRI) also help physicians to fine-tune the delivery of radiation to match a three-dimensional tumor site and spare more healthy tissue.
Proton beam therapies offer even more control when targeting tumors; however, these facilities require large particle accelerators, which are expensive. As a result, the cost of proton therapy is higher than the cost of conventional X-ray radiation therapy.
While more than 100,000 patients have been treated using particle beam therapies, and the technologies seem promising, especially for some inoperable tumors, there have been few clinical studies to demonstrate their overall effectiveness compared to conventional therapies. That’s partly because of the expense of the treatment and the limited number of facilities that can offer treatments. That should improve, since Hiramoto said he expects more facilities to be built, and the costs of treatment to decline.