Physics of ion beam therapy

Precision medicine along with other varied forms of treatment prepares us to face the challenge of cancer as the fact sheet (February 2018) of WHO informs that it is the second leading cause of death globally. Ion beam therapy is one of those preferred modes of treatment suitable for many malignant tumours - particularly those difficult to access through surgery. In the recent times treating the tumours with protons and heavy ions emerges as a favorable alternative to conventional photon therapy that uses gamma radiation from radioisotopes or high energy X-rays from electron linac. The advantages are related to the energy deposition characteristics of the ions and their linear energy transfer (LET), namely the Bragg curve and the Bragg peak in the depth-dose distribution. It is due to this peak that the effect of irradiation can be concentrated in the tumour and minimized in the healthy tissues preceding and following the tumour. The efficiency of the treatment is thus increased and the side effects reduced. Though precise and accurate, ion beam therapy is something of the Cadillac-a capital-intensive modality, but ideal for treating certain complex, hard-to-treat tumors