Surgical organ displacement: what is the best "materials and methods" for proton radiotherapy?

Chin J Cancer Res 2013;25(3):267-268 www.thecjcr.org In the mid 1940s, Robert Wilson (1) hypothesized that a highly localized deposition of energy from a proton beam could be used to increase the radiation dose to tumors while minimizing radiation to adjacent normal tissues. The depthdose distribution of a proton beam differs significantly from that of a photon beam. Protons show increasing energy deposition with penetration distance, reaching a maximumnamed the Bragg peak-near the end of the range of the proton beam. In front of the Bragg peak, the dose level is modest compared to photon beams; beyond the Bragg peak, the dose decreases to nearly zero. By choosing the appropriate proton beam energy, the depth of the Bragg peak can be adjusted to match the depth and extent of the target volume. Therefore, excellent conformality can be achieved, in contrast to conventional or intensity-modulated radiotherapy (IMRT). Protons have a higher linear energy transfer (LET) than photons, but their radiobiological properties do not differ substantially. In clinical applications, the absorbed dose is multiplied by a factor of 1.1 to convert the relative biological effectiveness (RBE) of a proton beam to cobalt gray equivalents (CGE) or gray equivalents (GyE) (2). In 1954, scientists at the Lawrence Berkeley Laboratory initiated the first studies of proton radiotherapy (PRT) to support Wilson’s hypothesis. Therefore, PBT has been studied for over a half a century, and more than 83,000 patients worldwide are reported to have been treated with proton beams (3-7). The most significant change to PRT occurred in the 1990s, when the Loma Linda University Medical Center began to use PRT clinically, and became the first hospital based medically dedicated proton therapy facility in the world (8). Since then, similar medically dedicated facilities have been constructed around the world. At present, almost 50 particle therapy facilities are operating worldwide, and it is estimated that the number of facilities will increase to 70-80 within 5-10 years. Despite these physical advantages, proximal and lateral dose is still the modest, and it never reaches to be zero. Therefore, if organs or structures that are sensitive to radiation located closely adjacent or abutting vulnerable, especially digestive tract, it is difficult to irradiate sufficient dose to the tumor. The article by Jesseph and colleagues in Translational Cancer Research described their single-institution experience of the use of surgical organ displacement in the treatment of abdominal, pelvic, or retroperitoneal tumors by PRT (9). The aim of this intervention is to make a space between tumor and digestive tract in order to perform PRT with a curative intent. Their findings are noteworthy. All of the 15 patients who did surgical organ displacement obtained adequate displacement to allow successful proton treatment planning. Furthermore, there were no surgical complications. These methods described by Jesseph et al. might not only allow us to irradiate sufficient dose to the tumor, but also expand indication of PRT.