Phantoms give a clearer picture of radiation effects

A new generation of realistic models of the human body could give radiation scientists and medical workers a better view of how exposure to radiation affects different internal organs. These so-called “voxel phantoms” offer a new way to reveal the effects of radioactive particles that have been ingested or breathed in or otherwise entered the body. (The word “voxel” means volume element and is the three-dimensional equivalent of pixel).

Maria Zankl of the Institute of Radiation Protection in Neuherberg, Germany, speaking at The Society for Radiological Protection`s Internal Dosimetry conference at the British Library today (23/10/02), describes how she and her colleagues are using voxel phantoms to help them understand how different organs are affected by the damaging energies of a radioactive material that has been taken up.

“When a radioactive substance gets inside you, it distributes throughout the body, into bones and organs, and these body sites themselves then become “radioactive sources”, Zankl explains. “These internal radiation sources can cause tissue damage and serious health problems, such as radiation sickness and cancer, depending on how much radioactive material was taken up.”

Until now, scientists have only been able to estimate very roughly how much of the energy from the radioactive material that is released in the “source organs” is absorbed by these organs themselves, and how much reaches other organs nearby and is absorbed there. This provides values of “organ doses” given that the spread of the radioactive material around the body is already known. These values allow health effects to be predicted but they cannot be measured directly so schematic models of the human body have been used to estimate the energy absorptions.

Zankl and her colleagues have recently assessed the use of body images (recorded with computerised tomography (CT) and magnetic resonance imaging (MRI)) of real people used to create far more realistic body models – “voxel phantoms”. These virtual apparitions provide a much clearer picture of the radioactive energy released and absorbed by the internal organs. “We have quantified how large the dose in different organs is, depending on the amount of radioactive material accumulated in the single source organs,” explains Zankl. “The new voxel phantoms are a clear improvement over previous ones, since they have a very realistic internal anatomy,” she adds, “and the organ distances are exactly the same as in a real person.”

Zankl revealed to the meeting that on the basis of her team`s results the International Commission on Radiological Protection (ICRP) will use voxel models for future dose calculations.