Traditionally external radiation for treating cervical cancer was given with four-field technique. That is radiation beams were directed from anterior, posterior, right and left lateral directions. This technique did not spare any of organs inside the pelvis.
With the invention of CAT scans, three-dimensional radiation therapy was developed. This technology was a CT-based radiation planning system which allowed sparing of normal tissues to some extent. Later on a sophisticated form of 3D conformal radiation therapy, called Intensity Modulated Radiation Therapy or IMRT was developed. This form of radiation planning software is an inverse planning system which begins with a desired dose distribution and arrives at a specification of the required fluence modulation to create it.
Obviously the more sophisticated these technologies get, the more successfully we can spare the normal tissues surrounding the target of radiation.
Nowadays an even more sophisticated technology called RapidArc Therapy, not only improves dose conformity but also significantly shortens treatment times. Volumetric modulated arc therapy differs from existing techniques like IMRT because it delivers dose to the whole volume, rather than slice by slice and the treatment planning algorithm ensures the treatment precision, helping to spare normal healthy tissue.