SECONDARY STANDARD CALIBRATION, MEASUREMENT AND IRRADIATION CAPABILITIES OF THE INDIVIDUAL MONITORING SERVICE AT THE HELMHOLTZ ZENTRUM MÜNCHEN: ASPECTS OF UNCERTAINTY AND AUTOMATION

Simulation of Hp(0,07) beta and photon response of a BeOSL finger ring dosemeter

Simulation of a dosemeter's energy and angular response lowers development cost and time. To support development of a new beta sensitive dosemeter we simulate both the dosemeter and the skin dose in a rod phantom as there are no fluence to dose conversion coefficients in the ICRU Report 47 for electrons. Published spectra for BSS2, N-Series and S-Cs and S-Co were used to define sources, with CAD models used to define the simulation geometry. Simulation tools were validated with experimental beta and photon responses available for the BeOSL photon ring. The developed toolchain was then used to simulate several iterations of a beta sensitive detector element inside a beta ring holder, with the goal to minimise the need for repeated prototype fabrication and characterisation. Simulation results for the final design were compared to measurements on 3D printed prototypes with all radiation qualities, except 90Sr/90Y 0°, falling within measurement uncertainty.

Protected and Unprotected Radiation Exposure to the Eye Lens During Endovascular Procedures in Hybrid Operating Rooms

OBJECTIVE

Radiation cataract has been observed at lower doses than previously thought, therefore the annual limit for equivalent dose to the eye lens has been reduced from 150 to 20 mSv. This study evaluated radiation exposure to the eye lens of operators working in a hybrid operating room before and after implementation of a dose reduction program.

METHODS

From April to October 2019, radiation exposure to the first operator was measured during all consecutive endovascular procedures performed in the hybrid operating room using BeOSL H_p(3) eye lens dosimeters placed both outside and behind the lead glasses (0.75 mm lead equivalent). Measured values were compared with data from a historic control group from the same hospital before implementation of the dose reduction program.

RESULTS

A total of 181 consecutive patients underwent an endovascular procedure in the hybrid operating room. The median unprotected eye lens dose (outside lead glasses) of the main operator was 0.049 mSv for endovascular aortic repair (EVAR) (n = 30), 0.042 mSv for thoracic endovascular aortic repair (TEVAR) (n = 23), 0.175 mSv for complex aortic fenestrated or branched endovascular procedures (F/BEVAR; n = 15), and 0.042 mSv for peripheral interventions (n = 80). Compared with the control period, EVAR had 75% lower, TEVAR 79% lower, and F/BEVAR 55% lower radiation exposure to the unprotected eye lens of the first operator. The lead glasses led to a median reduction in the exposure to the eye lens by a factor of 3.4.

CONCLUSION

The implementation of a dose reduction program led to a relevant reduction in radiation exposure to the head and eye lens of the first operator in endovascular procedures. With optimum radiation protection measures, including a ceiling mounted shield and lead glasses, more than 440 EVARs, 280 TEVARs, or 128 FEVARs could be performed per year before the dose limit for the eye lens of 20 mSv was reached.

SIMULATION OF OSL AND TLD DOSEMETER RESPONSE FOR THE DEVELOPMENT OF NEW EXTREMITY DOSEMETERS

The individual monitoring service at the Helmholtz Zentrum München is currently developing a new eye lens dosemeter to be integrated in radiation protection glasses and a new ring dosemeter using a new BeOSL detector element for extremity dosimetry developed by Dosimetrics. In the design process for the new eye lens dosemeter, MCNP6 Monte Carlo simulations were used to model the energy and angular response of new dosemeters before ordering the expensive tools for injection molding. This study describes the simulation of the dosemeter and detector, and the involved calculations do obtain the response in terms of the radiation protection quantity Hp(3). Simulations were carried out also for existing whole body dosemeters and TLD rings in order to verify the MC tools. With the final dosemeter prototypes becoming available earlier this year, all MC models could be verified and show very good agreement with experimental data.

A FULLY AUTOMATED SECONDARY STANDARD X-RAY CALIBRATION FACILITY FOR PERSONAL DOSEMETERS

The individual monitoring service at the Helmholtz Zentrum München has extended the calibration facilities provided at the Munich IAEA/WHO secondary standard dosimetry laboratory with a new fully automated X-ray calibration facility for the calibration of personal dosemeters according to the ISO 4037 standard series. This work describes the X-ray irradiation system and the automated dosemeter transport system as well as the measurements performed to characterize the photon fields and to ascertain conformity to the ISO standard. Standard uncertainties of the radiation quantities provided by the system are given together with a discussion of some of the problems that are encountered in fulfilling the requirements of a matched field according to the latest drafts of the ISO 4037-1 standard.