Charged-particle beams consisting of protons or helium ions are a type of particulate radiation therapy that contrast with conventional electromagnetic (i.e., photon) radiation therapy due to the unique properties of minimal scatter as the particulate beams pass through the tissue, and deposition of the ionizing energy at a precise depth (i.e., the Bragg Peak). Thus radiation exposure to surrounding normal tissues is minimized. The theoretical advantages of protons and other charged-particle beams may improve outcomes but this has nto been proven. At the same time proton beam radiotherapy is significantly more expensive than other modalities.
An search of the literature demonstrates that there is the technical feasibility of proton three dimensional conformal, external beam partial breast irradiation (3D-CPBI) in 20 patients with fully excised node-negative, early stage breast cancer. In another publication of apparently the same group of 20 women, an analysis of cosmetic outcomes and tumor recurrence at 12 months is reported. The authors propose that 3D-CPBI using protons instead of standard photon therapy offers dose improve homogeneity to the tumor bed while sparing normal breast tissue from a radiation dose. In light of the lack of a randomized comparison group, short follow-up, small number of patients, and favorable prognoses of the enrolled patients, conclusions concerning the equivalence of 3D-CPBI to whole breast radiation therapy cannot be made.
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