Determination of the source dwell position of an afterloading device with a detector array

It was the aim to develop and test a measurement technique for the source position of an afterloading system using an electronic two-dimensional detector array (2D array). A "GammaMed plus IX" high dose rate afterloading device (Varian Medical Systems, Palo Alto, USA), and a Seven29 2D detector array (PTW Freiburg GmbH, Freiburg, Germany) have been used. A hollow needle has been connected to the afterloading device. Its outer diameter is 3.0 mm and its length about 220mm. A 14 mm thick Perspex slab was fixed in a reproducible position on the 2D array. Above the 14th detector row, a groove was cut in the slab which accommodates the hollow needle in a fixed position relative to the 2D array. In order to define the position of the source, the signals of the detectors in the 14th detector row have been evaluated. A theoretical curve depending on the source position and strength, has been fitted to the acquired detector signals. It has been shown that the reproducibility of the measurement technique - including the reproducibility of the source placement - was within 0.15mm. This method can not only replace film measurements, it is also more exact and less time consuming

MLC positioning checks and calibration with a portal imaging system

For checking the leaf positions of a MLC (Multi Leaf Collimator) images are acquired with an EPID (Electronic Portal Imaging Device) and then evaluated with a programme (MLC check) developed in-house. During image acquisition a Perspex tray with two metal markers of known position (in the radiation field) is inserted in the satellite tray holder. After determination of the marker positions within the image coordinate system, the image can be transformed to the radiation field coordinate system. This allows the exact determination of the leaf tip positions relative to the radiation field. This evaluation can be applied to images of arbitrary field shapes, provided they were acquired in the same geometry (EPID position, gantry and collimator angles). The entire measurement procedure is based on images in bmp (Windows Bitmap) format, with a 1024 x 1024 matrix and a pixel depth of 24 bit (8 bit per color channel). A suitable marker plate can be manufactured without sophisticated workload; thus the method may be easily and cost effectively adapted at other locations

Exposure of treating physician to radiation during prostate brachytherapy using iodine-125 seeds

Background and Purpose: Only sparse reports have been made about radiation exposure of the treating physician during prostate seed implantation. Therefore, thermoluminescence dosimeter (TLD) measurements on the index fingers and the backs of both hands were conducted. Material and Methods: Stranded iodine-125 seeds with a mean apparent activity of 27.4 MBq per seed were used. During application, the treating physician manipulated the loaded needle with the index fingers, partially under fluoroscopic control. Four physicians with varying experience treated 24 patients. The radiation exposure was determined with TLD-100 chips attached to the index fingertips and the backs of hands. Radiation exposure was correlated with the physician`s experience. Results: The average brachytherapy duration by the most experienced physician was 19.2 min (standard deviation sigma = 1.2 min; novices: 34.8 min [sigma = 10.2 min]). The mean activity was 1,703 MBq (sigma = 123 MBq), applied with 16.3 needles (sigma = 2.5 needles; novices: 1,469 MBq [sigma = 229 MBq]; 16.8 needles [sigma = 2.3 needles]). The exposure of the finger of the ``active hand`` and the back of the hand amounted to 1.31 mSv (sigma = 0.54 mSv) and 0.61 mSv (sigma = 0.23 mSv), respectively (novices: 2.07 mSv [sigma = 0.86 mSv] and 1.05 mSv [sigma = 0.53 mSv]). Conclusion: If no other radiation exposure needs to be considered, an experienced physician can perform about 400 applications per year without exceeding the limit of 500 mSv/year; for novices, the corresponding figure is about 200