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The establishment of radiological protection criteria for non-uniform skin exposures

Ziel

A COLLABORATIVE EXPERIMENTAL PROGRAMME WILL INVESTIGATE NON-STOCHASTIC EFFECTS IN MOUSE AND PIG SKIN AND STOCHASTIC EFFECTS IN MOUSE SKIN, FOLLOWING UNIFORM AND NON-UNIFORM ALPHA (A) AND BETA (B) IRRADIATION. THIS WILL ENABLE RADIOLOGICAL PROTECTION CRITERIA TO BE DEVELOPED FOR LIMITING NON-UNIFORM SKIN EXPOSURE AND WILL PROVIDE THE DESIGN PARAMETERS FOR PERSONAL SKIN DOSEMETERS. THE WORK IS PART OF A COLLABORATIVE PROGRAMME WITHIN THE FRAMEWORK OF THE EUROPEAN LATE EFFECTS PROJECT GROUP (EULEP) AND THE EUROPEAN RADIATION DOSIMETRY GROUP (EURADOS), BETWEEN THE CRC NORMAL TISSUE RADIOBIOLOGY RESEARCH GROUP CHURCHILL HOSPITAL, OXFORD, THE RADIOBIOLOGY DEPARTMENT OF THE MEDICAL COLLEGE OF ST. BARTHOLOMEW'S HOSPITAL, LONDON, AND OURSELVES. THE PRESENT PROJECT INVOLVES SPEDCIFICALLY THE PRODUCTION AND DOSIMETRY OF A RANGE OF ALPHA AND BETA RADIOACTIVE SOURCES.
A collaborative programme has been designed to investigate nonstochastic effects in mouse skin and pig skin, and stochatic effects in mouse skin, following uniform and nonuniform alpha irradiation and beta irradiation. This enables radiological protection criteria to be developed for limiting nonuniform skin exposure and provides the design parameters for personal skin dosimeters. In particular, identification of the nature and depth of cells at risk in the skin, and of an appropriate area over which doses should be averaged, has been carried out.

A collaborative programme is investigating nonstochastic effects in mouse and pig skin and stochatic effects in mouse skin, following uniform and nonuniform alpha and beta irradiation. This is enabling radiological protection criteria to be developed for limiting nonuniform skin exposure and providing the design parameters for personal skin dosimeters. In particular this identifies the nature and depth of cells at risk in the skin and selects an appropriate area over which doses should be averaged.
INITIAL EXPERIMENT DESIGNS HAVE FORMED THE BASIS OF CURRENT PILOT STUDIES AND THE ONGOING PROGRAMME DESCRIBED HERE HAS BEEN DESIGNED AS A COLLABORATIVE EFFORT. THE DATA WILL BE ANALYSED FROM THE VIEWPOINT OF THE PRACTICAL USER SO THAT THE PROJECT IS RELEVANT TO BOTH FUNDAMENTAL RADIOBIOLOGY AND PRACTICAL RADIOLOGICAL PROTECTION.
THE AIM OF THE PROGRAMME IS TO ANSWER A NUMBER OF PRACTICAL RADIATION PROTECTION QUESTIONS RELEVANT SPECIFICALLY TO SKIN, BUT ALSO OF GENERAL RELEVANCE TO OTHER TISSUE SYSTEMS:
1. IS THERE A THRESHOLD AREA BELOW WHICH NO DETRIMENTAL EFFECT IS OBSERVED, IRRESPECTIVE OF RADIATION DOSE?
2. WHAT ARE THE THRESHOLD DOSES FOR DESQUAMATION AND ULCERATION AS A FUNCTION OF THE AREA IRRADIATED AND THE RADIATION QUALITY?
3. HOW DO THE THRESHOLD DOSES DEPEND ON DOSE RATE/FRACTIONATION?
4. WHAT IS THE RADIOBIOLOGICAL EFFECTIVENESS (RBE) FOR ALPHA RADIATION FOR NON-STOCHASTIC ENDPOINTS?
5. HOW ARE THE NON-STOCHASTIC EFFECTS DEPENDENT ON MORPHOLOGICAL AND BIOLOGICAL DIFFERENCES BETWEEN SPECIES AND HOW CAN THE ANSWERS TO QUESTIONS 1-4 BE EXTRAPOLATED TO MAN?
6. OVER WHAT AREA AND DEPTH SHOULD SKIN DOSE BE ASSESSED IN ORDER TO PROVIDE A SINGLE-DOSE PARAMETER TO DESCRIBE THE VARIOUS NON-STOCHASTIC EFFECTS OVER THE WHOLE RANGE OF B ENERGIES OF PRACTICAL INTEREST? (THIS WOULD PROVIDE A RATIONAL BASIS FOR DEFINING AN ANNUAL DOSE LIMIT AND FOR PROVIDING THE DESIGN PARAMETERS FOR A PERSONAL SKIN DOSEMETER).
7. WHAT ANNUAL DOSE LIMIT FOR SMALL AREA EXPOSURES OF HUMAN SKIN WILL PREVENT DETRIMENTAL NON-STOCHASTIC EFFECTS?
THE EXPERIMENTAL PROGRAMME WILL INVOLVE PARALLEL STUDIES WITH PIGS (DR. HOPEWELL) AND MICE (DR. COGGLE). AREAS OF SKIN WILL BE IRRADIATED USING A RANGE OF DIFFERENT-SIZED SOURCES OF THREE DIFFERENT BETA EMITTERS: PM-147 (EMAX 0.225 MEV), TM-170 (EMAX 0.97 MEV) AND SR/Y-90 (EMAX 2.27 MEV) AND CM-244 ALPHA SOURCES (EMAX 5.8 MEV). IN-HOUSE SOURCES WILL BE PRODUCED TO PROVIDE DOSE RATES FROM 10 TO THE POWER OF MINUS 1 TO 10 TO THE POWER OF 4 GY H TO THE POWER OF MINUS 1 OVER AREAS FROM 1 MM TO THE POWER OF 2 TO 10 CM. STRONTIUM AND PROMETHIUM SOURCES WILL BE BASED ON COMMERCIAL DESIGNS WITH FIELD-REDUCING FILTERS WHERE NECESSARY. THULIUM SOURCES WILL BE PRODUCED BY NEUTRON ACTIVATION OF ULTRA-PURE METAL FOILS. VARIOUS AREA CURIUM 244 ALPHA SOURCES WILL BE PROVIDED BY USING POLYSTYRENE FIELD-REDUCING FILTERS ON AN ELECTRO-DEPOSITED SOURCE.
ISODOSE AND CENTRAL AXIS DEPTH DOSE DATA WILL BE MEASURED USING AN EXTRAPOLATION CHAMBER WITH POLYSTYRENE ABSORBER FOILS. AN INTERCOMPARISON PROGRAMME UNDER THE AUSPICES OF THE BETADOS GROUP OF EURADOS WILL PROVIDE AN OPPORTUNITY FOR STANDARDISATION. DOSE ESTIMATES WILL ALSO BE PROVIDED USING ULTRA-THIN THERMOLUMINESCENT DOSEMETERS AND SOURCE UNIFORMITY CHECKS WILL BE MADE USING FILM DENSITOMETRY.

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