Abstract
The number of facilities offering radiotherapy with protons or heavier ions is continuously increasing; worldwide, more than 160 000 patients have been treated with protons, and more than 25 000 with heavier ions. Despite this substantial clinical experience, there is still a need for further developments and improvements which are specific to the properties of particle beams. This contribution briefly summarizes the main physical and radiobiological properties of ion beams which make them favorable for application in tumor therapy. In addition, major challenges that are currently addressed in different research areas are reviewed. These comprise the fields of biophysical modeling, treatment planning, mitigation of target motion and novel approaches based on particular spatio-temporal beam delivery techniques.
Highlights
I ON BEAM therapy represents a rapidly developing branch of radiotherapy, mainly using proton beams and - to a lower extent - heavier ions like, e.g., carbon ion beams
After the proposal by Wilson [1] to use ion beams for medical applications, first clinical applications were implemented with proton beams at Berkeley in 1954 [2] and in 1957 at Uppsala [3]; treatments with He beams were initiated in 1957 and with heavier ions in 1975 at Berkeley [2]
Gensheimer et al [39] analyzed an overshoot of the proton beam visible in MR images; this overshoot effect might be attributable to an increased RBE at the distal edge [37]
Summary
I ON BEAM therapy represents a rapidly developing branch of radiotherapy, mainly using proton beams and - to a lower extent - heavier ions like, e.g., carbon ion beams. Whereas this property is shared by all ion species, in particular heavier ions like carbon ions show an additional advantage with respect to their biological effectiveness. They exhibit an increased biological effectiveness in particular toward lower energies, i.e., in the region where they come to rest when penetrating tissue (the so-called “Bragg peak”). Lateral scattering of heavier ions is substantially reduced as compared to protons, allowing to spare normal tissue at the side of treatment fields. The curves for ion irradiation are steeper, but at the same time the shape of the dose response curves changes, as they typically get straighter as compared to the shouldered shape of survival curves observed after conventional photon radiation. The RBE varies with energy and with the stopping power of the ions as characterized by the linear energy transfer (LET)
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