Air kerma to HP(3) conversion coefficients for photons from 10 keV to 10 MeV, calculated in a cylindrical phantom

Abstract

In the framework of the ORAMED project (Optimization of RAdiation protection for MEDical staff), funded by the European Union Seventh Framework Programme, different studies were aimed at improving the quality of radiation protection in interventional radiology and nuclear medicine. The main results of the project were presented during a final workshop held in Barcelona in January 2011, the proceedings of which are available in the open literature. One of the ORAMED tasks was focused on the problem of eye-lens photon exposure of the medical staff, a topic that gained more importance especially after the ICRP decision to lower the limiting equivalent dose to 20 mSv per year. The present technical note has the scope, besides briefly summarising the physical reasons of the proposal and the practical implications, to provide, in tabular form, a set of air kerma to Hp(3) conversion coefficients based on the adoption of a theoretical cylindrical model that is well suited for reproduction of the mass and the shape of a human head.

AIR KERMA TOHp(3) CONVERSION COEFFICIENTS FOR IEC 61267 RQR X-RAY RADIATION QUALITIES: APPLICATION TO DOSE MONITORING OF THE LENS OF THE EYE IN MEDICAL DIAGNOSTICS

“…h pK (3,RQR,0) conversion coefficients were calculated for RQR qualities and for a varying angle of incidence from 0 to 180º by implementing the interpolation technique suggested by Behrens (8) . Conversion coefficients for monoenergetic photon beams were taken from Gualdrini et al (6) . The following steps were considered: (a) Firstly, the photon fluence spectra (dφ/dE) for the radiation qualities of interest were determined from the XCOMP5 program (15) .…”

“…(b) Subsequently, the average conversion coefficients h pK (3, RQR, α) were calculated by applying the following equation: h pK (3, Ei, α) correspond to mono-energetic photons for the ICRU cylindrical phantom calculated by Gualdrini et al (6) The formula represents the ratio between dose equivalent at 3 mm depth and air kerma, calculated for the radiation quality of interest RQR. In the equation, dφ/dE is the fluence per unit energy and Vmax is the voltage applied to the X-ray tube to generate the radiation beam.…”

“…This proposal was based on anatomical considerations, since this geometry is closer to the mass and shape of the head than the 30x30x15 cm 3 ISO slab phantom (5) . The authors (6) also provided conversion coefficients from air kerma to H p (3) for mono-energetic photon fields and for some X-ray beams of interest. Behrens (2010) published a complete series of h pK (3,R,α) for ISO 4037-1 (7) qualities using a slab phantom and later on in 2012 he published a series for the cylindrical phantom (8,9) .…”

Report of IRPA task group on issues and actions taken in response to the change in eye lens dose limit

“…After publication of the ICRP statement in 2011, the definition of the operational quantity, H p (3), suitable for estimating the equivalent dose to the lens of the eye H lens , and the associated calibration procedure were reviewed in relation to application to occupational dosimetry. This was achieved through the work of ENEA (Gualdrini et al 2013) and CEA-LNHB (Daures et al 2011) within the frame work of the ORAMED project (Vanhavere et al 2012) providing H p (3) dosemeters for direct measurements that could avoid the use of surrogate quantities.…”

IAEA Tec Doc-1731 ‘Implications for Occupational Radiation Protection of the New Dose Limit for the Lens of the Eye’

“…In the past, the slab phantom (as used for whole body dosimeters for the quantity H p (10)) was suggested for the quantity H p (3) [59]. Recently, a cylinder phantom has been suggested [60,61,62]. Investigations show that using the new cylinder phantom instead of the well-established slab phantom does not significantly improve the quality of measurements except for high incidence angles (larger than 75°: at 90° only the cylindrical phantom can be used for type testing) [63].…”