A brief review on prompt-gamma-based approaches for range verification in particle therapy

Particle therapy exhibits a sharp distal dose falloff at the end of the range, known as the Bragg peak (BP), which offers significant advantages over conventional photon therapy. However, this modality also brings out several challenges due to various range uncertainties. For instance, even a minor shift in BP can result in severe changes to the treatment quality. Therefore, effective range control of particle therapy is essential to spare the normal tissues behind the tumor from inevitable irradiation. Prompt gamma (PG) measurements, which detect gamma rays induced by impinging particles within nanoseconds, enable real-time in-vivo range verification. To date, although numerous PG detection approaches employing spatial, spectral, and timing information of PG are under investigation, only PG imaging with a knife-edge slit camera has been tested in clinical practice. This article reviews the principles, development, and current challenges of PG-based methods for range verification in particle therapy.