A radiation source of a brachytherapy apparatus includes: a hot cathode heated for generating free electrons, which are emitted to a target element and form an electron beam under an accelerating electric field a focusing element partially enclosing the hot cathode and having a focusing electric field through which the electron beam passes for reducing the diameter thereof an anode tube configured to enter a lesion or a lumen of an applicator a target element positioned at an end of the anode tube and generating radiation in response the impact of the electron beam and a control module configured to control the focusing electric field of the focusing element, thereby adjusting a diameter of the electron beam.一種近端治療裝置的放射源,包括:一熱陰極,被加溫以產生游離電子,該游離電子受一加速電場的作用而射向一靶元件而形成一電子束;一聚焦元件,部分圍繞該熱陰極,並具有一聚焦電場,該電子束通過該聚焦電場而縮小其直徑;一陽極管柱,被構造以進入一病變處或是一施用器的內腔中;該靶元件,位於該陽極管柱的末端,被該電子束撞擊而產生放射;以及一控制模組,被構造以控制該聚焦元件的聚焦電場,從而調整該電子束的直徑大小。1‧‧‧放射源10‧‧‧陰極組件11‧‧‧陰極、熱陰極、熱絲12‧‧‧聚焦元件20‧‧‧陽極組件21‧‧‧靶元件22‧‧‧陽極管柱31‧‧‧饋通引線40‧‧‧殼體
