Stereo X ray photogrammetry applied for prevention of sigmoid-colon damage caused by radiation from intrauterine sources.

Radiation therapy of cervix carcinoma is applied in this Institute by means of a modified Stockholm method in combination with external beam irradiation. In 1968, parametrial portals were replaced by large planparallel opposed fields extending cranially to LIII/LIV with central shielding in order to avoid overdosage in the area of intracavitary treatment. This resulted in a marked increased incidence of severe sigmoid-colon radiation lesions from 0.25% to 4%; predominantly in Stage I and II patients. Therefore two measures have been introduced: beginning in 1972 measures were taken to prevent the cranial displacement of the uterus during intracavitary treatment in order to avoid shortening the distance between the radioactive sources and the sigmoid-colon; from 1972 stereo X ray photogrammetry (SMR) was applied for dose determinations at points of the sigmoid-colon, which were seen to be located close to the applicator. When SRM data indicated that a high dose at the sigmoid-colon might occur, treatment modifications enabled prevention of radiation damage. Change of position of the applicator was the first to be considered. In the last seven years no surgical intervention had to be performed because of a sigmoid-colon lesion resulting from an unexpected high radiation dose delivered by intrauterine sources. The local recurrence rate was not increased following treatment modifications for prevention of sigmoid-colon radiation damage.