Angular Dependence Factors and Air Kerma to Dose Equivalent Conversion Coefficients for Cylindrical Phantoms Irradiated by Plane-Parallel Extended Monoenergetic Photon Beams

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Abstract
With the aid of the Monte Carlo method, conversion coefficients between the receptor-free air collision kerma and the collision kerma for 4-element ICRU tissue have been calculated at a depth of 0.007 g.cm-2 in circular cylinder phantoms irradiated by broad plane-parallel photon beams in a direction perpendicular to the cylinder main axis. The phantom material was ICRU tissue or PMMA; the phantom diameter 1.9 cm, 7.3 cm, of 30 cm; the phantom length 30 cm. The calculations were performed for monoenergetic photons in the energy range between 4 keV and 1.25 MeV. The conversion coefficients can be used in the field of extremity dosimetry to convert measured kerma or exposure values into personal dose equivalents: the results for the 7.3 cm diameter cylinder phantoms for the calibration of wrist or ankle dosemeters; those for the 1.9 cm diameter phantoms for the calibration of finger dosemeters. In addition to the conversion coefficients, their angular dependence factors in the middle plane of the phantoms perpendicular to the main axis were also studied. Such quantities for the ICRU tissue phantoms are necessary in the procedure for type testing extremity dosemeters on rod or pillar phantoms.

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