To see the explosive rise of proton-beam therapy, an expensive and controversial cancer treatment, look to the billboards of Belgium.

Ion Beam Applications SA, the Belgian company that leads the global market for huge proton-beam machines, is selling so many systems lately that it needs to boost its 1,200-strong workforce by 400 workers. It launched a big recruitment drive across the country this year, featuring radio and newspaper spots along with dozens of billboards and posters.

“It was very difficult to escape the IBA campaign,” said Chief Executive Olivier Legrain.

Proton-beam therapy is a form of cancer radiotherapy that uses positively charged particles to kill tumor cells. Unlike traditional radiotherapy using X-rays, protons can be programmed to deposit most of their energy in the tumor, minimizing damage to surrounding, healthy tissue. X-rays, in contrast, lose energy as they move through the body, meaning that tissue between the tumor and the beam will receive a higher dose of radiation than the tumor itself.

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The technology has been around since the 1980s, but until recently demand was muted due to high cost and limited evidence that it makes financial sense. Proton-beam therapy centers can cost up to $200 million to build and are more expensive to operate than traditional radiotherapy. While that higher price tag is justified for treating childhood cancers and a small number of adult cases, such as tumors in the base of the skull, the jury is still out on its cost-effectiveness for most common cancers. For some countries, that meant it was cheaper to send patients abroad for treatment: since 2008, the U.K. has sent its patients to centers in the U.S., which has led the way in adopting proton-beam therapy.

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