Dosimetric characterization of a synthetic single crystal diamond detector in clinical radiation therapy small photon beams.

PURPOSE: To determine the potentialities of synthetic single crystal diamond Schottky diodes for accurate dose measurements in radiation therapy small photon beams. METHODS: The dosimetric properties of a diamond-based detector were assessed by comparison with a reference microionization chamber. The diamond device was operated at zero bias voltage under irradiation with high-energy radiotherapic photon beams. The stability of the detector response and its dose and dose rate dependence were measured. Different square field sizes ranging from 1 × 1 cm(2) to 10 × 10 cm(2) were used during comparative dose distribution measurements by means of percentage depth dose curves (PDDs), lateral beam profiles, and output factors. The angular and temperature dependence of the diamond detector response were also studied. RESULTS: The detector response shows a deviation from linearity of less than ±0.5% in the 0.01-7 Gy range and dose rate dependence below ±0.5% in the 1-6 Gy∕min range. PDDs and output factors are in good agreement with those measured by the reference ionization chamber within 1%. No angular dependence is observed by rotating the detector along its axis, while ∼3.5% maximum difference is measured by varying the radiation incidence angle in the polar direction. The temperature dependence was investigated as well and a ±0.2% variation of the detector response is found in the 18-40 °C range. CONCLUSIONS: The obtained results indicate the investigated synthetic diamond-based detector as a candidate for small field clinical radiation dosimetry in advanced radiation therapy techniques.

Measuring the imaged-object distance with a stationary high-spatial-resolution scintillation camera.

A method to measure the detector-to-object distance from the images obtained with stationary high-spatial-resolution gamma-ray cameras for in vivo studies has been developed. It exploits the shift of the imaged object in the image plane, obtained at a certain tilt of the parallel-hole collimator. A linear dependence of the image displacement on the distance to the object has been measured using a high-spatial-resolution scintillation camera employing an yttrium-aluminium perovskite (YAP) scintillator. It is shown that the modified YAP camera can be used to obtain three-dimensional information without moving the camera or the object. The method could be applied in scintimammography and radioguided surgery, in lymphoscintigraphy, as well as in the analysis of the biodistribution of radiopharmaceuticals.

Performance measurements of a high-spatial-resolution YAP camera.

Physical properties of a position-sensitive camera for the analysis of biodistributions of gamma- and beta-emitting radiopharmaceuticals in small animals have been studied, in order to achieve optimal operating conditions. The camera consisted of a highly segmented yttrium-aluminate perovskite (YAP) scintillator, coupled to a position-sensitive photomultiplier. The energy resolution, the detection efficiency, the spatial resolution, the spatial linearity and the count-rate linearity of the YAP camera have been determined. Images related to initial activity levels and successive biodistribution evolution in mice organs are presented as an illustration of the camera performance.

99mTc-MIBI scintimammography using a dedicated nuclear mammograph.

UNLABELLED: This study reports on a prototype single-photon emission mammograph (SPEM) dedicated to 99mTc-hexakis-2-methoxyisobutile isonitrile (MIBI) scintimammography. Main technical features are reported together with physical performance. Preliminary patient data are also reported. METHODS: The SPEM detector head is composed of a CsI(T1) scintillating array coupled to a Hamamatsu R3292 position-sensitive photomultiplier tube with crossed-wire anode. The high-resolution collimator is 35-mm thick with a 1.7-mm hole diameter and a 0.2-mm septal thickness. The electronic acquisition system is composed of five integrated cards with computation based on high-speed programmable microprocessors. The readout electronics include correction maps for on-line energy correction and spatial uniformity. The small size of the detector head allows the use of mechanical breast compression to minimize detection distance and tissue scatter. After physical SPEM performance evaluation in vivo scintimammography was performed in 29 patients and was compared with a state-of-the-art Anger camera. RESULTS: The SPEM showed an intrinsic spatial resolution of 2 mm, an energy resolution of 23% FWHM at 122 keV and spatial uniformities of 18% (integral) and 13.5% (differential). The SPEM imaged one 0.4-cm carcinoma missed by the Anger camera and resolved as separate lumps an irregular focal uptake on the Anger camera image. The remaining cases yielded concordant results. CONCLUSION: The SPEM prototype presented in this study shows adequate physical characteristics for 99mTc-MIBI scintimammography.