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DEVELOPMENT OF REALISTIC PHANTOMS TO ASSIST THE INTERPRETATION OF IN VIVO MEASUREMENTS OF LOW ENERGY PHOTON-EMITTING RADIONUCLIDES IN BONE

Objective

THE OBJECTIVE OF THIS STUDY IS TO DESIGN AND CONSTRUCT PHANTOMS WHICH CAN BE USED TO CALIBRATE DETECTORS FOR THE IN VIVO MEASUREMENT OF LOW-ENERGY PHOTON EMITTING RADIONUCLIDES IN BONE.
Research is directed towards the production of skull and chest phantoms suitable for the calibration of detectors for the measurement of americium-241, lead-210 and strontium-90 in bone. Information has been obtained on the initial skeletal distribution of bone surface seeking radionuclides in man from measurements on subjects injected with yttrium-88 and neptunium-239. To improve methods of assessing intakes and body content of bone seeking radionuclides an improved model of plutonium biokinetics has been developed for assessing systemic uptake of plutonium from excretion measurements.
SEVERAL RADIONUCLIDES OF RADIOLOGICAL IMPORTANCE, E.G. 241-AM, 210-PB AND 90-SR, DEPOSIT IN BONE AND MAY BE DETECTED THERE BY IN VIVO MEASUREMENTS TECHNIQUES, USUALLY BY THE MEASUREMENT OF ACTIVITY IN THE SKULL. FOR MEASUREMENTS OF TRANSURANIC ACTIVITY IN THE LUNGS, ACTIVITY DEPOSITED IN THE RIBS MAY PRESENT AN INTERFERENCE THAT SHOULD BE QUANTIFIED. DIFFICULTIES IN CALIBRATION ARISE BECAUSE THE PHOTON EMISSIONS OF THESE RADIONUCLIDES ARE PREDOMINANTLY OF LOW ENERGY AND THEREFORE SUBJECT TO CONSIDERABLE ATTENUATION IN THE BODY TISSUES. IN ORDER TO CALIBRATE DETECTORS FOR SUCH MEASUREMENTS, IT IS NECESSARY TO PROVIDE A PHANTOM WHICH ACCURATELY REPRESENTS THE PHOTON ATTENUATION PROPERTIES OF THE RELEVANT PART OF THE BODY AND IN WHICH KNOWN ACTIVITIES ARE DISTRIBUTED AS THEY WOULD BE IN A CONTAMINATED SUBJECT. IT IS ANTICIPATED THAT IN GENERAL PHANTOMS MAY BE CONSTRUCTED BY APPLYING RADIOACTIVE MATERIAL TO THE SURFACES OF THE BONE STRUCTURES AND BUILDING UP SOFT-TISSUE-EQUIVALENT MATERIALS ON THESE STRUCTURES TO REPRESENT UNDERLYING AND OVERLYING TISSUES. A PRELIMINARY PART OF THE STUDY WILL BE TO CARRY OUT CALCULATIONS TO TEST WHETHER ACTIVITY DEPOSITED ON THE INNER AND OUTER SURFACES OF A BONE STRUCTURE CAN ADEQUATELY REPRESENT ACTIVITY DISTRIBUTED IN THE BONE AS IT WOULD BE FOLLOWING INTAKE. THE POSSIBLITIES OF USING BOTH HUMAN BONES AND BONE SUBSTITUTE STRUCTURES WILL BE INVESTIGATED. TECHNIQUES WILL BE DEVELOPED FOR APPLYING RADIOACTIVITY TO BONE SURFACES IN A CONTROLLABLE MANNER AND FOR APPLYING ACCURATELY CONTROLLED THICKNESSES OF TISSUE SUBSTITUTE MATERIALS TO BONE STRUCTURES.
THE PRIMARY AIM OF THE STUDY WILL BE TO PRODUCE SKULL PHANTOMS SUITABLE FOR THE CALIBRATION OF DETECTORS FOR THE MEASUREMENT OF 241-AM, 210-PB AND 90-SR IN BONE. THE SECONDARY AIM OF THE STUDY WILL BE TO PRODUCE CHEST PHANTOMS SUITABLE FOR THE CALIBRATION OF DETECTORS FOR THE ASSESSMENT OF THE INTERFERENCE ARISING FROM THE PRESENCE OF 241-AM AND PLUTONIUM ISOTOPES IN BONE. IN THE LAST PART OF THE STUDY, THE PHANTOMS PRODUCED WILL BE USED IN INTERCALIBRATION EXERCICES BETWEEN IN VIVO MEASUREMENT LABORATORIES IN THE EUROPEAN COMMUNITY.
IN THE INITIAL PHASE OF THE PROJECT, CALCULATIONS WILL BE CARRIED OUT TO ASSESS:
(A) WHETHER ACTIVITY DEPOSITED ON THE SURFACES OF BONES OR BONE EQUIVALENT CAN ADEQUATELY REPRODUCE THE PHOTON SPECTRUM EXPECTED FROM ACTIVITY REALISTICALLY DISTRIBUTED IN BONE (BOTH THE ATTENUATION OF LOW-ENERGY PHOTONS AND THE BREMSSTRAHLUNG PRODUCTION SPECTRUM WILL BE CONSIDERED);
(B) THE TISSUE EQUIVALENCE OF AVAILABLE SOFT-TISSUE SUBSTITUTES.
A LITERATURE SEARCH WILL BE UNDERTAKEN TO DEFINE AVERAGE SKULL DIMENSIONS AND AVERAGE THICKNESSES OF TISSUE OVERLYING THE SKULL BONES.
THE AVAILABILITY OF HUMAN SKULLS WILL BE EXAMINED. THE POSSIBILITY OF CONSTRUCTING ARTIFICIAL SKULLS FROM BONE EQUIVALENT MATERIAL WILL ALSO BE INVESTIGATED.

Funding Scheme

CSC - Cost-sharing contracts

Coordinator

NATIONAL RADIOLOGICAL PROTECTION BOARD (NRPB)
Address
Chilton
OX11 0RQ Didcot
United Kingdom