Proton Radiation Therapy

Compared to a photon beam, a proton beam has some unique features that make it a particularly attractive option for treatment of liver tumors. Proton Radiation is a relatively new technology that is only available at a few sites in the U.S. First, it has a low “entrance dose” (the dose delivered along the path of the beam from the surface of the skin to the front of the tumor), thus minimizing the dose to healthy tissues in front of the tumor and potentially reducing treatment-related side-effects. Second, it has virtually no “exit dose” beyond the tumor, again reducing the dose to healthy tissues. Third, in the case of liver tumors, it travels through homogenous tissue (liver) to get to the tumor, making it less likely that changes in tissue density along its path may modify its characteristics (range of penetration). Lastly, it is able to deliver a very potent dose of radiation directly to the tumor.

Capitalizing on these unique characteristics of the proton beam, a very focused treatment can be achieved for the treatment of liver tumors. An illustrative example of a radiation treatment plan is shown below. Here the tumor is denoted in stippled blue while the remaining liver is outlined in dark blue to the right of the tumor. The circular lines surrounding the tumor are different doses seen by tissues. The white line that is closest to the tumor delivers a very potent dose of radiation while the orange line denotes a dose than is less than half the dose represented by the white line. There is considerable sparing of the healthy liver and the spinal cord (marked in red) by the orange line (less than half the dose delivered to the tumor).

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Proton Radiation Therapy