A brief overview of the use of proton beam radiotherapy for gastrointestinal cancers

In 1946, almost 50 years after the discovery and implementation of X-rays for the treatment of cancer, Dr. Robert Wilson at Harvard University proposed that proton beams could have potential clinical benefit (1). The first cancer patient was treated with proton beam therapy (PBT) in 1954 at the Lawrence Berkeley Laboratory, a high energy physics research facility in California. Only seven years later, the Harvard Cyclotron Laboratory opened in Boston, Massachusetts in 1961 and treated more than 9,000 patients with PBT over the next 40 years. The bulk of this experience was in the treatment of inoperable, radioresistant tumors that were superficial and/or of simple geometry and amenable to treatment with a fixed horizontal beam, such as ocular melanoma, prostate cancer, and sarcoma (2,3). The first hospital-based PBT center opened in 1990 at Loma Linda University in California. The Paul Scherrer Institute in Switzerland opened in 1996 the first compact gantry capable of administering pencil beam scanning intensity modulated proton therapy (IMPT). In the United States, MD Anderson Cancer Center in Texas initiated treatment in 2008 with a rotating gantry capable of administering pencil beam scanning IMPT. This ushered in a new era of modern PBT facilities capable of treating large, complex targets at essentially any site in the body. In 2015, Washington University commenced treatment with the first commercially available single room, compact proton accelerator and gantry, reducing the initial cost of investment to open a PBT center. As of December 2018, there are 30 PBT centers in operation in the United States (21 multi-room facilities and 9 single room facilities) and 45 PBT centers in operation outside of the United States, mostly in Asia and Europe (4).