In vivo clinical dosimetry with LiF: PTFE dosimeters

The purpose of this report is to describe the implementation of a dosimetric system suitable for ''in vivo'' measurements in some clinical applications. This system is based in re-usable thermoluminiscent dosimeters of Lithium fluoride embebded in teflon (PTFE). The results obtained in the utilization of these dosimeters for the determination of entrance absorbed doses on an antropomorphical phantom and patients are also presented. The irradiations have been made in several anatomical localizations with 60Co gamma rays. A great number of measurements has been made to determine properly the precision that can be reached with LiF: PTFE dosimeters. A considerable improvement of this precission has been obtained calibrating individually each dosimeter. The effects of the remanent sensibilization of the dosimeters that have received relatively high doses (approx. 1 Gy) are also reported. In order to take into account this unwanted effect it is necessary to calibrate frequently the dosimeters during their useful life, lowering, in this way, the risk of making wrong assignation of absorbed doses. From the results obtained in the measurements of absorbed doses in patients, it is clearly deduced that, even in anatomical localizations without special difficulties, such as the abdominal: flat and without problems to maintain the treatment position, rather high discrepancies can be found between the planned doses and those really imparted in practice. These results confirms the usefulness of making patient dose measurements in order to have effective control of the necessary quality of the therapeutical treatments. (author)