3DCRT

Three-dimensional conformal radiotherapy (3DCRT) is an external beam radiotherapy technique that uses three-dimensional imaging to shape radiation beams to the geometry of a tumor. Planning relies on computed tomography (CT) scans to delineate target volumes—the gross tumor volume, clinical target volume, and planning target volume—and to identify nearby organs at risk. Dose prescriptions aim to cover the target while limiting exposure to healthy tissues.

In practical terms, 3DCRT uses multiple fixed radiation beams whose openings are shaped by a multileaf collimator (MLC). The treatment planning system optimizes the arrangement and weight of these beams to produce a dose distribution that conforms to the target in three dimensions. Beams are typically chosen to balance coverage and sparing of critical structures, with dose constraints assessed through dose–volume histograms. Treatment is delivered on a linear accelerator and may involve image-guided verification, such as portal imaging or cone-beam CT, to ensure accurate patient setup.

Compared with older two-dimensional techniques, 3DCRT provides improved conformality and better sparing of some normal tissues. It is distinct from intensity-modulated radiotherapy (IMRT), which uses modulated fluence to achieve even tighter dose shaping. Nevertheless, 3DCRT may be limited by organ motion, radiation dose to inhomogeneous regions (such as lung or head and neck anatomy), and the need for precise imaging and immobilization. It remains widely used for a range of sites, including brain, head and neck, prostate, and thoracic or abdominal tumors, where reliable target localization and motion management are feasible.