Medical Physics · 1996 · 108 citations · 0 references
MedicineOncologyRadiation OncologyRadiation DosimetryRadiation MeasurementTreatment PlanningExternal Beam DosimetryExternal Beam RadiotherapyIonization Chamber DosimetryRadiation TherapyStereotactic RadiosurgeryMiniature Ionization ChambersParallel-plate Ionization Chamber DosimetryParallel-plate Ionization ChambersSpectrum AnalysisStereotactic Radiosurgery DosimetryTumor DosimetryX-ray DosimetryX-ray Imaging Systems
A miniature, battery operated 40 kV x-ray device has been developed for the interstitial treatment of small tumors ( < 3 cm diam) in humans. X rays are emitted from the tip of a 10 cm long, 3 mm diameter probe that is stereotactically inserted into the tumor. The beam, characterized by half-value layer (HVL), spectrum analysis, and isodose contours, behaves essentially as a point isotropic source with an effective energy of 20 keV at a depth of 10 mm in water. The absolute output from the device was measured using a parallel plate ionization chamber, modified with a platinum aperture. The dose rate in water determined from these chamber measurements was found to be nominally 150 cGy/min at a distance of 10 mm for a beam current of 40 microA and voltage of 40 kV. The dose in water falls off approximately as the third power of the distance. To date, 14 patients have been treated with this device in a phase I clinical trial.