8. Evaluation of a new system for in-vivo dosimetry based on MOSFET detectors

Abstract

Purpose

: In Holycross Cancer Centre in Kielce in vivo dosimetry is performed with new miniature detectors called MOSFET. MOSFETs are advertised by Thomson & Nielsen company as almost ideal detector for in-vivo dosimetry: they are isotropic, can be treated as point detector fully transparent to treatment beam, having zero temperature and negligible energy effect, can be used either for electron and photon radiation, in teletherapy and brachytherapy, can be used in several QA procedures, very easy and convenient for handling and very low time consuming. Our experience both from extensive tests and clinical use will be presented.

Results

: From our experience MOSFETs detectors can be treated as isotropic, are fully transparent for radiation, can be used both in teletherapy and brachyterapy. For application in brachyterapy special catheters with lead localisation markers must be used. The energy dependence cannot be considered as negligible. For 6 and 15 MV X photons calibration factors differ of about 5%. Reproducibility depends strongly on the dose. It decreases very much for very small doses (for dose 60 cGy – 1 standard deviation is of 2,5%). Very useful advantage of MOSFET detectors is their applicability for surface dose measurements. More details will be presented during the congress.

Conclusion

: MOSFET detectors can be effectively used for in-vivo dosimetry in tele and brachytherapy. The reproducibility should be improved.