Brachytherapy photons

No distinct advantage has been noted when other forms of external beam irradiation, other than photons, or brachytherapy have been used. Neutron irradiation has not proven to be better than photons for stage III inoperable NSCLC (14,15). The use of brachytherapy has been limited to endobronchial treatment for palliation or as a boost after external beam. There have been institutional reports of interstitial brachytherapy, also usually done as aboost. Neither of these two approaches has been shown to be superiorto external beam (16,17). 

Brachytherapy physics is concerned with electrons, whether primary or secondary, as in the case of photon sources (Table 1). 

Figure 3 Microdosimetric distributions for several photon radiations commonly used in brachytherapy. (From Ref. 36.)...

Another isotope, however, is beneficial for treating cancer, especially of the prostate. Cesium 131 has a half-life of only 10 days and emits low-energy photons that can be used to destroy cancer cells. Injection of a small source or"seed"of the radioisotope to a specific site—a process called brachytherapy—allows radiation to be aimed like bullets that can damage target receptor cells. It is especially potent against those that divide rapidly like cancer cells. 

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