What is the role of proton beams in the treatment of prostate cancer?

Updated: Nov 29, 2018
  • Author: Isamettin Andrew Aral, MD, MS; Chief Editor: Edward David Kim, MD, FACS  more...
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Answer

Conventional external beam radiation therapy (EBRT) is delivered via photon beams. Data from Loma Linda and Harvard suggest that prostate cancer can be effectively managed with conformal proton beam therapy. [24] What is less clear is whether the overall cost-benefit ratio will make this form of therapy a continued source of clinical interest. [25]

Photons are packets of energy that are capable of entering the body to a depth that is proportional to their energy (ie, higher energy equals deeper penetration). Photons are generated for clinical use in linear accelerators by accelerating electrons to varying potentials (speeds) and aiming them at a tungsten target.

The resultant collision of the electron with the target generates a photon beam whose energy is proportional to the accelerating potential of the electron. Energies of commonly used clinical beams range from 4 to 25 MV.

The electron is a relatively small particle with essentially no weight. Consequently, the equipment needed to accelerate the electron before it collides with the target is comparatively small. In contrast, other charged particles (eg, protons) have as much as 2000 times the mass of an electron. Accordingly, the equipment needed to accelerate these particles is significantly larger; in fact, it can require up to several thousand square feet of space.

A unique feature of proton beam therapy is the way in which it deposits its most concentrated radiation dose. Unlike photon beam therapy, the entrance radiation dose tends to be significantly less than the maximum energy of the clinical beam. Proton beams have a characteristic Bragg peak. Beyond this point, where energy is at a maximum intensity level, radiation energy rapidly falls off, which is important in the management of normal tissue toxicity.

Technologic advances in proton beam therapy have resulted in the construction of several centers throughout the United States. Although costs remain in excess of $100 million per unit, this technology has generated significant interest in the management of prostate carcinoma.

Proton beam therapy has been successfully used in the management of prostate cancer. Early work from the cyclotron center at Harvard formed an important basis for current clinical trials. [26]


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