Diversification of existing reference phantoms in nuclear medicine: Calculation of specific absorbed fractions for 21 mathematical phantoms and validation through dose estimates resulting from the administration of (18)F-FDG.

Current dose assessment in nuclear medicine patient studies relies on published S-values, which are, in turn, based on calculated specific absorbed fractions (SAFs) available for a limited number of anthro-pomorphic computational phantoms. In order to take the individual physiognomy of patients more into account, this study aimed to broaden the supply of phantoms and their respective SAFs. An ensemble of 21 mathematical phantoms was submitted to the Monte Carlo Code MCNP4c2 for the purpose of calculation of SAFs for annihilation radiation. These values were incorporated into an internal dose assessment following the Medical Internal Radiation Dose (MIRD) schema and relying on published biokinetic data for intravenous administration of (18)F-FDG. The results were compared with data from the ICRP, MIRD reports and concurrent calculations with OLINDA/EXM. A very good agreement with sources relying on the SAFs of Cristy and Eckerman (i.e., the ICRP and OLINDA/EXM) was observed, with the absorbed dose in lung being the only exception. In the case of dose to red marrow, the King Spiers factors were omitted in the three-factor approximation, which led to a precise accordance with the Cristy/Eckerman values. Summarizing, one can say that the coincidence with published data justifies the method chosen and demonstrates successfully the expansion of available reference phantoms for dose assessment in nuclear medicine.

Outdoor workers' acceptance of personal protective measures against solar ultraviolet radiation.

The acceptance and usability of personal protection against solar UV radiation was evaluated in a field study with a group of tinsmiths in Austria. The personal protective measures (PPM) tested involved four categories: shirts, headwear, sunglasses and topically applied sunscreens; at least six different products per category were tested. Recommendations for the "ideal" shirt, headwear, pair of sunglasses and topical sunscreen are given based on data from questionnaires, i.e., from the point of view of the workers, independently from the actual physical level of protection (such as low transmittance or area of coverage) provided. It is argued that in practice it is important to consider the acceptance and usability of protective measures as well as the level of physical protection when providing PPM.

Performance analysis of a film dosimetric quality assurance procedure for IMRT with regard to the employment of quantitative evaluation methods.

A system for dosimetric verification of intensity-modulated radiotherapy (IMRT) treatment plans using absolute calibrated radiographic films is presented. At our institution this verification procedure is performed for all IMRT treatment plans prior to patient irradiation. Therefore clinical treatment plans are transferred to a phantom and recalculated. Composite treatment plans are irradiated to a single film. Film density to absolute dose conversion is performed automatically based on a single calibration film. A software application encompassing film calibration, 2D registration of measurement and calculated distributions, image fusion, and a number of visual and quantitative evaluation utilities was developed. The main topic of this paper is a performance analysis for this quality assurance procedure, with regard to the specification of tolerance levels for quantitative evaluations. Spatial and dosimetric precision and accuracy were determined for the entire procedure, comprising all possible sources of error. The overall dosimetric and spatial measurement uncertainties obtained thereby were 1.9% and 0.8 mm respectively. Based on these results, we specified 5% dose difference and 3 mm distance-to-agreement as our tolerance levels for patient-specific quality assurance for IMRT treatments.

Application of the heliocentric potential to aircraft dosimetry.

The heliocentric potential is the result of a steady-state solution to the diffusion equation of cosmic rays through the solar wind. The counting rate of any high-latitude, ground-level neutron monitor can be used to determine this potential, which will return cosmic ray spectra in real time. These spectra are routinely used to determine the radiation dose rate to which air crew are exposed during the precise hours of a flight, including the effects of quick decreases and Forbush decreases. Further, it has been used in an effort to calculate the radiation dose rate to air crew during an energetic solar particle event, as the cosmic ray background before the event must be determined. An alternate approach is to use the deceleration potential, which assumes a significant time-dependence of cosmic rays through the heliosphere. However, the theory behind it does not account for the behaviour of ground-level neutron monitors.