What is the definition or description of: brachytherapy?

Brachy means: "short", so that the isotopes used have short range of active dose and rapid fall-off of the dose so as to not give the healthy tissues the highest damaging radiation, and the implanted tumor get very high dose, locally confined treatment.

Internal radiation: It specifically translates to close or near theray , as in the location of the treatment. It encompasses a wide variety of techniques used in many different situations that include both permanent and temporary, low or hugh dose rate, intracavitary as well as implanted use of particle based radiation usually in the form of a type of seed that is placed inside or alongside a tumor or surgical site.

The Most Targeted RT: 'Brachy' literally means "arm's length" which represents the short distance that the radiation travels, This is typically achieved with radioactive or electronic sources that are either permanently placed into the tumor region (i.,e prostate) and give radiation slowly (low-dose rate) or temporarily placed within catheters in tumor regions (i.e breast ) and deliver high-dose rate RT.