Proton Therapy Delivery and Its Clinical Application in Select Solid Tumor Malignancies

Abstract

Radiation therapy is a frequently used modality for the treatment of solid cancers. Although the mechanisms of cell kill are similar for all forms of radiation, the in vivo properties of photon and proton beams differ greatly and maybe exploited to optimize clinical outcomes. In particular, proton particles lose energy in a predictable manner as they pass through the body. This property is used clinically to control the depth at which the proton beam is terminated, and to limit radiation dose beyond the target region. This strategy can allow for substantial reductions in radiation dose to normal tissues located just beyond a tumor target. However, the degradation of proton energy in the body remains highly sensitive to tissue density. As a consequence, any changes in tissue density during the course of treatment may significantly alter proton dosimetry. Such changes may occur through alterations in body weight, respiration, or bowel filling/gas, and may result in unfavorable dose deposition. In this manuscript, we provide a detailed method for the delivery of proton therapy using both passive scatter and pencil beam scanning techniques for prostate cancer. Although the described procedure directly pertains to prostate cancer patients, the method may be adapted and applied for the treatment of virtually all solid tumors. Our aim is to equip readers with a better understanding of proton therapy delivery and outcomes in order to facilitate the appropriate integration of this modality during cancer therapy. Video Link The video component of this article can be found at https://www.jove.com/video/58372/ The basic principles behind RT are straightforward. With the application of radiation, energy is deposited into cells through the ionization of atoms. This energy, though it may raise the temperature of an irradiated region by only a few microkelvin, produces free radicals that can directly damage exposed cells by way of DNA injury 12,13. Much of our understanding of high-energy particle radiation and its interaction with matter comes from theoretical and experimental studies of cosmic rays and their interactions in the upper atmosphere carried out in the early 20 th century 14. High-energy (MeV to GeV) charged particles interact with matter primarily via the electromagnetic force: as these particles pass

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