What Is the Contribution of Brachytherapy in Tailoring Local Therapy?

Abstract

Brachytherapy is a generic term to describe radiation techniques using short (less than 6 cm) focus surface distance (FSD). It is in contrast with “teletherapy,” usually performed using linear accelerators and a long FSD (80 cm or more) often called external beam radiation therapy (EBRT). The dose distribution in brachytherapy depends for a major part on the inverse square law which implies that with a short FSD (1–6 cm), the radiation dose fall off is very rapid (percentage depth dose close to 50% at 0.5 cm from the “surface dose”). The smaller the FSD (≤ 1 cm), the more rapid is the dose gradient. This fall off (and dose inhomogeneity) is mainly independent of the beam energy (between 50 kV and 1.3 mV). Using 50 kV with an FSD of 4 cm produces at 5 mm depth a dose of 65% of surface dose compared to only 30% when using Iridium 192 (300 kV) with a FSD of 1 cm. Broadly speaking, brachytherapy can be performed with two general approaches:

• 1. Radionuclide brachytherapy usually with iridium 192 (or with iodine 125 or cobalt 60 etc.). Positioning of the radioactive sources can be interstitial, intracavitary (endoluminal), or onto skin surface mold. The implant can be removable or permanent (iodine 125).

• 2. Contact X-Ray 50 kVp brachytherapy (CXB) for accessible and limited lesions (skin, intracavitary, intraoperative).

Disclosure

Jean Pierre GERARD is the medical advisor of the Ariane Medical Systems company Derby; UK