Image-Guided Proton Therapy: A Comprehensive Review

SIMPLE SUMMARY: In proton therapy, there is a sharp peak in the delivered dose followed by a rapid falloff, known as the Bragg peak, which is not present in photons. This allows for treatment plans that deliver lower doses to normal tissue than can be performed with photons. This requires a high degree of accuracy and precision of delivery due to the short distance between an area of high and low doses. Image guidance allows for better visualization of the target and more accurate delivery of proton (and photon) radiation. The equipment used to deliver proton therapy differs in several ways from that of photon radiation, which impacts the methods used for image guidance in proton therapy. This paper aims to summarize the various methods of image guidance in current proton therapy and their relative advantages and disadvantages, as well as areas for future improvements. ABSTRACT: Image guidance for radiation therapy can improve the accuracy of the delivery of radiation, leading to an improved therapeutic ratio. Proton radiation is able to deliver a highly conformal dose to a target due to its advantageous dosimetric properties, including the Bragg peak. Proton therapy established the standard for daily image guidance as a means of minimizing uncertainties associated with proton treatment. With the increasing adoption of the use of proton therapy over time, image guidance systems for this modality have been changing. The unique properties of proton radiation present a number of differences in image guidance from photon therapy. This paper describes CT and MRI-based simulation and methods of daily image guidance. Developments in dose-guided radiation, upright treatment, and FLASH RT are discussed as well.