Proton therapy for gastrointestinal cancers

Proton beam therapy provides an opportunity to deliver ionizing radiation with improved dose conformity. It has gained popularity as a means of more localized radiation delivery. However, proton therapy data are still lacking, as there are still relatively few proton treatment centers worldwide. This paucity of data is particularly evident in gastrointestinal (GI) cancers. Most GI cancers are located in close proximity to or abut critical organs. The ability to deliver an appropriate dose to a target in this area is challenging; normal organ toxicities often limit the amount of radiation that can be delivered to achieve a therapeutic dose. The modern trend in treatment of GI cancers is toward multimodality treatment. However, there is an increased risk of toxicity when combining modalities such as radiotherapy, chemotherapy, and surgery, thus placing an even greater emphasis or normal-tissue toxicities.

Improvements in radiation treatment techniques over the past few decades have allowed dose escalation with improved normal-tissue sparing. The driving force behind improving treatment conformity is the significant short- and long-term morbidity of normal tissue toxicity during and after radiation treatment. The degree of normal-tissue sparing within individuals undergoing radiation treatment is highly variable and depends on tumor type and region. Tumors of the esophagus, for example, are surrounded by lung and spinal cord, while anal cancers are in close proximity to the bladder and rectum. Each subsite of the GI tract requires different techniques and approaches to maximize normal-organ sparing while delivering adequate amounts of radiation to the tumor. The physical properties of proton radiation may offer a distinct benefit in treating GI malignancies.