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Ever since the first proton beam therapy (PBT) treatment in 1954 at University of California, Berkley, the use of PBT worldwide has rapidly increased.1 Due to the depth-dose characteristics of protons that allow for steep fall-off just distal to the tumor target, PBT can reduce unnecessary radiation dose to nearby normal tissues and allow for safer dose escalation in select clinical scenarios. Superior normal tissue avoidance can lead to reductions in acute and late toxicities, safe dose escalation can lead to improved local control, and the combination of both factors has the potential to impact overall survival (OS).
Early data have suggested that PBT led to improved clinical outcomes in the treatment of various pediatric cancers, ocular melanomas, sarcomas of the paravertebral region, and brain tumors when compared with traditional photon-based radiation.2 Historically, fewer studies evaluated the utility of PBT in the treatment of gastrointestinal (GI) malignancies; however, retrospective studies in the setting of gastroesophageal cancer and pancreatic cancer show that preoperative PBT may reduce postoperative complications and definitive PBT may improve outcomes for those with unresectable disease.3–6 Even fewer studies have evaluated the role of PBT in the primary or neoadjuvant treatment of colorectal cancer (CRC), but there have been published clinical outcomes in the treatment of recurrent disease as well as liver metastases. The aim of this review is to discuss the existing dosimetric and clinical data for PBT in the treatment of patients with CRC.