Proton Therapy

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Key points

  • Proton therapy is a form of external beam radiotherapy that has several key advantages over conventional photon (x-ray) radiotherapy.

  • Unlike x-rays, protons deposit their maximum dose at a specific depth, with no exit dose to normal tissues, exploiting a phenomenon known as the Bragg peak.

  • Lack of exit dose allows for delivery of a therapeutic radiation dose to tumors in challenging anatomic locations.

  • Reduction in integral dose (low-dose bath) to normal tissues may reduce the risk of late

Expansion and use of single-room centers

Until recently, the costs associated with developing and operating a proton center have been a key drawback. Traditional multiroom centers—typically housing 4 to 5 proton treatment rooms—have cost between $100 million and 300 million to build, with estimated annual operating costs of $15 million to $25 million.18 These centers typically have required bread-and-butter cases—breast cancer and prostate cancer—to economically sustain the center and subsidize the rare, complex cancers most likely to

Key clinical areas of use

The National Comprehensive Cancer Network guidelines currently support the use of proton therapy in various scenarios across more than 40 distinct cancer types,23 and several clinical trials are currently randomizing patients to proton therapy versus x-ray radiotherapy (Table 1).20 The following sections highlight selected key disease sites in which proton therapy may offer key advantages over conventional radiotherapy.

Future directions for research and use

Future directions for in silico and in vivo research aim to improve the understanding of the physics and biology of proton therapy and how these differ versus those of conventional photon radiation. Specifically, learning exactly where the Bragg peak occurs has key clinical implications, because proton depth dose uncertainty currently requires strategies that involve either treating a margin of normal tissue to ensure tumor coverage or avoiding a margin of tissue to avoid a key organ at risk.

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    Disclosure Statement: M.J. LaRiviere, P.M.G. Santos, C.E. Hill-Kayser: nothing to disclose. J.M. Metz: advisory boards for Varian, IBA, and Provision.

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