Targeting cancer cells

GSI Helmholtzzentrum für Schwerionenforschung

The object of radiotherapy in oncology is to destroy tumor cells while sparing surrounding, healthy tissues. This requires maximizing the physical dose of radiation as well as the biological effectiveness in the tumor while minimizing them in healthy tissues. Accelerated ions meet these objectives far better than the commonly used X-rays.

Physical dose distribution

As an X-ray beam penetrates the body, the dose is at a maximum just beneath the skin and then decreases progressively at greater depths until the "remnant beam” emerges on the far side. Ions, on the other hand, penetrate into the body and unfold their damaging effects at the end of their flight path in a specific depth, which depends on the speed of the ions. The dose along that route i. e. in the healthy tissue is low. But the dose of radiation reaches a sharp peak in the small—pinhead-sized—tissue volume in which the ions come to a stop. By controlling the speed of the ions, the depth at which this dose maximum occurs can be located precisely within the tumor. The dose in healthy tissue remains very small.

Biological effectiveness

At the cellular level, the goal of radiotherapy is to cause irreparable damage to the genetic material of the cancer cells. This damage leads to the death of the cells. The biological effectiveness of ion radiation in introducing genetic damage into the cancer cells is significantly greater than that of X-rays. As a result, it is possible to achieve much greater tumor damage at a given physical dose without causing additional damage to healthy tissues.

Dose distribution for X-ray and ion beams in biological tissues.
GSI Helmholtzzentrum für Schwerionenforschung