CT-Image Guided Brachytherapy

The name “Brachytherapy” is derived from ancient Greek words for short distance (brachios) and treatment (therapy) and refers to the therapeutic use of encapsulated radionuclides placed within or close to the tumor. Brachytherapy (BT), used as an integral part of cancer treatment for almost a century, developed in last three decades a rapid growth with the development of afterloading devices and the introduction of artificial radionuclides. The impressive progress of three dimensional (3D) imaging, the rapidly increasing speed and capacity of computers, and the sophisticated techniques developed for the treatment planning, opened a new era. Brachytherapy plays a crucial role in the curative treatment of many tumors. CT and/or MRI compatible applicators allow a sectional image based approach with a better assessment of GTV (Gross Tumor Volume) and CTV (Clinical Target Volume) compared to traditional approaches. Accurate and reproducible delineation of GTV and CTV, as well as healthy (critical) organs, has a direct impact on treatment planning, especially it is possible to optimize the reference isodoses to the target. A two-film typical localization technique does not allow the definition of the threedimensional (3D) extensions of the planning target volume (PTV) and organs at risk (OARs). Furthermore, using traditional dosimetry systems the dose report is related to the geometry of the implant and not to the target volume. In modern BT both treatment planning and plan evaluation have to be based on real 3D volume of the PTV and OARs.