In order to assess human organ doses for risk estimates under natural and man made radiation exposure conditions, human phantoms have to be used. As an improvement to the mathematical anthropomorphic phantoms, a new family of phantoms is proposed, constructed from computer tomographic (CT) data. A technique is developed which allows any physical phantom to be converted into computer files to be used for several applications. The new human phantoms present advantages towards the location and shape of the organs, in particular the hard bone and bone marrow. The CT phantoms were used to construct three dimensional images of high resolution; some examples are given and their potential is discussed. The use of CT phantoms is also demonstrated to assess accurately the proportion of bone marrow in the skeleton. Finally, the use of CT phantoms for Monte Carlo (MC) calculations of doses resulting from various photon exposures in radiology and radiation protection is discussed.

The organ doses for r rays from typical environmental sources were determined with Monte Carlo calculations using anthropomorphic phantoms having different body sizes. It has been suggested that body weight is the predominant factor influencing organ doses for environmental r rays, regardless of sex and age. A weight function expressing organ doses for environmental r rays was introduced. This function fitted well with the organ doses calculated using the different phantoms. The function coefficients were determined mathematically with the least squares method. On the assumption that this function was applicable to organ doses for human bodies with diverse characteristics, the variances in organ doses due to race, sex, age and difference in body weight of adults were investigated. The variations of organ doses due to race and sex were not significant. Differences in body weight were found to alter organ doses by a maximum of 10% for r rays over 100 keY, and 20% for low-energy r rays. The doses for organs located deep inside a body, such as ovaries, differed between a newborn baby and an adult by a maximum factor of 2 to 3. For r rays over 100 keY, the variation was within a factor of 2 for all organs. The organ doses for adolescents more than 12 years agreed within 15% with those of the average adult.

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The question discussed in this paper is whether effective dose can reflect the risk to patients from radiological procedures and can be used, for example, to optimise procedures and compare risks of various methods, to define dose constraints, and to estimate the risks to individuals or populations attributed to medical exposures. This report demonstrates that the use of effective dose for patients could be misleading or even wrong due to inappropriate simplifications of the underlying biological mechanisms and inappropriateness of the weighting factors connected with the definition of effective dose for a given patient population. We show that the choice of the most meaningful quantities to express patient exposure depends strongly on the respective situation.

In a recent recommendation, the International Commission on Radiological Protection substituted the effective dose equivalent, HE, with a similar quantity--the "effective dose," E--changing both the set of organs considered and the respective weighting factors. To quantify the impact of these changes, calculations of E and HE were performed for various photon energies and external irradiation geometries using a Monte Carlo code and mathematical anthropomorphic phantoms to which an esophagus was introduced for this purpose. For energies greater than 15 keV, E less than HE, the difference depending on photon energy and exposure geometry.