Traditionally external radiation for treating endometrial cancer was given with four-field technique. That is radiation beams were directed from anterior, posterior, right and left lateral sides. This technique did not spare any of organs within pelvis.
With the invention of CAT scans, three-dimensional radiation therapy was developed. This technology was a CT-based treatment planning system which allowed sparing of adjacent 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.