M. Sommer

Dose reduction in computed tomography: the effect of eye and testicle shielding on radiation dose measured in patients with beryllium oxide-based optically stimulated luminescence dosimetry

The aim of this study was to assess the effect of eye and testicle shielding on radiation dose to the lens and the testes of patients undergoing CT examinations. Fifty-one male patients underwent CT twice with identical protocols initially without, the second time with protective garments. Doses to the testes and the lenses were recorded with beryllium oxide-based dosimeters. The dose to the testes and lenses from CT exposure was reduced by 96.2% ± 1.7% and 28.2% ± 18.5%, when testicle and eye shielding was used, respectively. The effect of the eye shielding on the eye lens dose was found to depend on the x-ray tube position when the eye is primarily exposed during the scan. The maximum eye lens dose reduction achieved was found to be 43.2% ± 6.5% corresponding to the anterior position of the tube. A significant correlation between the patient’s body mass index and dose exposure could not be found. Eye and testicle shields, apart from being inexpensive and easy to use, were proven to be effective in reducing eye lens and testicle radiation dose burden from CT exposures.

Scintillation properties of the YVO4:Eu3+ compound in powder form: its application to dosimetry in radiation fields produced by pulsed mega-voltage photon beams

The investigation of scintillation properties of europium doped yttrium orthovanadate shows the suitability of this material for fiber-based dose rate measurements. All measurements were carried out with a 6 MV Varian linear accelerator. The temperature dependence of the signal is lower than that of the plastic scintillators reported so far. By measuring the afterglow of probes between Linac-pulses, the signal due to the stem effect can be successfully eliminated. Comparison of depth dose profiles in a water phantom for radiation field dimensions between 1 x 1 cm(2) and 10 x 10 cm(2) shows that the probes are suitable for small fields having dimensions up to 1 x 1 cm(2). The high light yield of probes having dimensions of 1 mm opens up the possibility for their use in spatially confined radiation fields, such as in intensity-modulated radiotherapy (IMRT) and volume-modulated radiation therapy (VMAT).

PROPERTIES OF THE BEOSL DOSIMETRY SYSTEM IN THE FRAMEWORK OF A LARGE-SCALE PERSONAL MONITORING SERVICE

The Individual Monitoring Service of the Helmholtz Zentrum München is currently using the BeOSL dosimetry system for monitoring ∼15 000 persons per month. This dosimetry system has a modular structure and represents a complete new concept on handling dosemeters in a large-scale dosimetry service. It is based on optically stimulated luminescence dosemeters made of beryllium oxide. The dosimetric and operational properties of the system are shown and discussed.

ENVIRONMENTAL DOSIMETRY WITH THE BeOSL PERSONAL DOSEMETER

In the course of this work, a dosemeter for measurement of ambient dose equivalent H*(10) based on the BeOSL dosimetry system was designed. Calculations of the energy response of the two-element BeOSL personal dosemeter in terms of H*(10) showed that the response does not fulfil the requirements of IEC 62387 Especially, the response for photon energies of 60-100 keV is too low. It is possible to correct this under-response using a BeOSL two-element dosemeter, a linear algorithm and an additional cover for the dosemeter. The Hp(0.07) element is shielded with lead, and with the help of a linear algorithm, corrections of the energy response are possible. So, the national requirements for an H*(10) area dosemeter in Germany can be fulfilled. The requirements of IEC 62387 are fulfilled for angles of radiation incidence from 0° to 60° for a rotation around the vertical and horizontal axis through the dosemeter, whereas for angles of incidence from 75° to 90°, the requirements are only fulfilled for rotation around the vertical axis through both elements.