VOL.
51, N O . 601 Correspondence
The great majority of diagnostic procedures now utilize compounds labelled with technetium 99m for which the gonad dose is typically in the range 100 to 200 mrad. The consequence of employing a criterion at least ten times as severe as that originally recommended by the ICRP would be that the "ten-day rule" would have to be applied to the majority of patients undergoing these investigations. No one would deny the need to apply proper precautions in the best interest of patients so as to avoid undesirable radiation exposure. However, the criteria used should represent a sensible balance between relative risks and benefits. This is especially true of the "ten-day rule" which is very awkward to apply in practice. So far no evidence has been presented which would justify the MRC Isotope Advisory Panel's recommended much severer criterion for the application of the "ten-day rule" than that originally envisaged by the ICRP. Yours, etc.
(1973) and Spiers (1969). Both label the ordinate axis ratio of absorbed dose rather than ratio of ionization produced. Now under equilibrium conditions the ratio of absorbed dose in copper to absorbed dose in carbon is equal to the ratio of the mass energy absorption coefficients for the particular photon energy considered. In the case of y rays from 60 Co this ratio is equal to 0.92, using data obtained from Knipe (1975). This signifies that under equilibrium conditions the absorbed dose in the carbon is slightly greater than the absorbed dose in the copper. However, the graphs with relabelled ordinate axes predict this same ratio to be 1.46, i.e. they predict that under electronic equilibrium the absorbed dose in copper is 1.46 times the absorbed dose in carbon. Now, one of the aims of Dutreix and Bernard's article (1966) is to investigate the underdosage and overdosage of tissue in the transition zone between tissue and a metal surface. The mistake is therefore not a trivial one. R. SEAR. The following shows how the discrepancy can be resolved: Radioisotope Department, mSz Dz=k U—^-^rad (1) The London Hospital, mSair Whitechapel, London E1 1BB where Dz = absorbed dose in a volume element of material REFERENCES Z BRITISH INSTITUTE OF RADIOLOGY, 1975. Irradiation of U = ionization produced in the air ionization human subjects for medical research. BIR Bulletin 1, 2, chamber 4-6. k — conversion factor for absorbed dose in air, INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION. rad/R=0.869 Publication 9, 1966. Recommendations of the ICRP mSz _ mass stopping power ratio of material Z (Pergamon Press, Oxford). mSair relative to air. OSBORN, S. B., 1977. Restricted applicability of the "ten-day Dutreix et al. (1962) found that for y rays from 60Co and rule". British Journal of Radiology, 50, 606. for the situation studied, the mean energy of the electrons Report of a WHO/IAEA consultation on the use of ionizing which form the electron flux in the equilibrium state is ef the radiation on human beings for medical research and train- order of 10 keV. Thus the ratio of the mass stopping powers ing including the use of radioactive materials. November should be calculated for a mean electron energy of 10 keV. 6-10, 1972. (Geneva, Report WHO/RHL/73.1). ICRU Handbook 78 (1959) gives (table 8.6) stopping power Report of a working party of the MRC Isotope Advisory ratios for 60Co y rays as 1.02 and 0.68-0.75 for C/air, Cu/air Panel on the application of the "ten-day rule" in radio- respectively. Dutreix and Bernard found experimentally that pharmaceutical investigations. 1977. British Journal of the ratio of ionization in carbon to that in copper under Radiology, 50, 200-202. equilibrium conditions is 0.69. Using equation (1) and the SEAR, R., 1974. Radioisotopes and the "ten-day rule". stopping power ratios quoted, the ratio of absorbed dose in British Journal of Radiology, 47, 822. the carbon to that in the copper under equilibrium conditions is 0.97. This agrees well with the predicted value of 0.92 found from the ratio of the mass energy absorption coefficients. THE EDITOR—SIR, It is to be hoped that future reproductions of the results of INTERFACE DOSIMETRY The study of an article in the March 1966 issue of this Dutreix et al., will not contain this error. Yours, etc., Journal (Dutreix and Bernard, 1966) has brought to light an D. LOWE. error of translation that appears to have gone unnoticed. Effectively the article summarizes in English work on Department of Nuclear Science and Technology, interface dosimetry carried out at the Institut G. Roussy, Royal Naval Colege, Villejuif, France, and previously published in French in a Greenwich, London SE10. number of articles, viz: Dutreix et al. (1962), Dutreix et al. (1964), and Dutreix and Bernard (1965). REFERENCES Briefly, the authors made ionization measurements in the BURLIN, T. E., SIDWELL, J. M., and WHEATLEY, B. M., 1973. Applications of Monte Carlo methods in medical radiology vicinity of a carbon/metal interface irradiated by y rays British Journal of Radiology, 46, 398-399. from 60Co and X rays in the energy range 10 MV to 20 MV. These measurements made possible the determina- DUTREIX, J., DUTREIX, A., and BERNARD, M., 1962. Etude de tion of the dose absorbed by a water equivalent medium la dose au voisinage de l'interface entre deux mileux de (carbon) in contact with a body of higher atomic number. It composition atomique differente exposes aux rayonnewas found that in the neighbourhood of the interface there ment et du 60Co. Physics in Medicine and Biology, 7, was an extremely rapid variation of dose, characterized by 69-82. the occurrence of peaks at a distance of 20-40 mg/cm2 behind DUTREIX, J., DUTREIX, A., BERNARD, M., and BETHENCOURT, the interface. These distributions were represented graphicA., 1964. Etude de la dose au voisinage de l'interface entre ally; the ordinate axis was labelled the ratio of ionization deux milieux de composition atomique differente, exposes in material Z to the ionization in carbon in the region where a des RX de 11 a 20 MV. Annales de Radiologie, 7 (3-4), 233-241. electronic equilibrium is established — U/Uc in the originals. One of these plots was reprinted in Dutreix and Bernard DUTREIX, J., and BERNARD, M., 1965. Etude de flux des (1966) Fig. 1, p. 206), the only difference being that the electrons secondaires et de leur retrodiffusion. Applicaordinate axis was now labelled the ratio of absorbed dose in tion a la determination de l'ionisation a l'interface entre material Z to absorbed dose in water in electronic equilibdeux milieux differents exposes a des RX de haute rium conditions—D/De. The assumption was made, thereenergie. Biophysik 2,179—192. fore, that U/Uc=D/De. I have found reproductions of this 1966. Dosimetry at interfaces for high energy X and selfsame graph in two other publications, viz: Burlin et al. gamma rays. British Journal of Radiology, 39, 205-210.
60
JANUARY
1978
Correspondence ICRU, 1959. Report of the International Commission on Radiological Units and Measurements. National Bureau of Standards (U.S.) Handbook 78. KNIPE, A. D., 1975. A revision of photon interaction data in the UKAEA nuclear data library. AEEW-M1368. SPIERS, F. W., 1969. Transition Zone Dosimetry. In Radiation Dosimetry, Ed. F. H. Attix, W. C. Roesch and E. Tochilin, Vol. Ill, pp. 809-867 (Academic Press, New York).
There has been correspondence in these columns recently about this topic (Farmer, 1976; Nicholson, 1976; Davies, 1977; Isherwood, 1977) but written from the rather different viewpoint of finding a name to describe and distinguish between X-ray transmission section scans, and radioisotope emission section scans. It seems to us that the problem is really much wider than this. Confusion may be caused by names based on initials (for example, TCAT and ECAT for transmission and emission computerized axial tomographs) which are only really understood by the "inner clique"; or new uses of the classical languages, which are often obscure to the uninitiated (e.g. zeugmatography for nuclear magnetic resonance imaging); or upon commercial names (e.g. EMI scan) which will not apply in a hospital with a machine of another manufacturer. It would be better to concentrate on combinations of commonly used and accepted names of any reasonable origin. This is more likely to be acceptable and come into common parlance, thereby clarifying the confusion. Yours, etc.,
THE EDITOR—SIR, NOMENCLATURE IN SCANNING INVESTIGATION
Since radioisotope (or radionuclide!) investigations are no longer unique in having a "scanning" procedure, the term has now become ambiguous. In-patients who have left the ward "to go for a scan" are becoming increasingly difficult to trace. In Aberdeen there are separate locations for gamma camera studies, rectilinear scanning, in vivo uptake tests and whole body counting, ultrasonic and thermographic studies, and X-ray cerebral scanning (EMI scanner). While the efficiency of having one word for one investigation is admirable, we really ought to be qualifying the word "scan" as a routine or else abandoning it altogether. Since there is little hope of abandoning it, the simplest solution is for the people who perform the investigations to be more specific in their terminology and make the effort of saying radioisotope scan, X-ray scan, ultrasound scan or thermal scan. Within each category again simple but specific terminology would keep everyone informed for example, with radioisotope scans there are conventional views and tomographic or section views. The important thing is to establish a working terminology which everyone in the hospital will understand and use in the interest of the patient.
W. I. KEYES, J. R. MALLARD.
Department of Medical Physics, University of Aberdeen, Foresterhill, Aberdeen AB9 2ZD REFERENCES DAVIES, E. R., 1977. Computerized tomographic scan terminology. British Journal of Radiology, 50, 77. FARMER, F. T., 1976. Terminology in computerized imaging. British Journal of Radiology, 49, 815. ISHERWOOD, I., 1977. Computerized tomographic scan terminology. British Journal of Radiology, 50, 374. NICHOLSON, J. P., 1976. New terminology needed. British Journal of Radiology, 49, 653.
61
51, N O . 601 Correspondence
The great majority of diagnostic procedures now utilize compounds labelled with technetium 99m for which the gonad dose is typically in the range 100 to 200 mrad. The consequence of employing a criterion at least ten times as severe as that originally recommended by the ICRP would be that the "ten-day rule" would have to be applied to the majority of patients undergoing these investigations. No one would deny the need to apply proper precautions in the best interest of patients so as to avoid undesirable radiation exposure. However, the criteria used should represent a sensible balance between relative risks and benefits. This is especially true of the "ten-day rule" which is very awkward to apply in practice. So far no evidence has been presented which would justify the MRC Isotope Advisory Panel's recommended much severer criterion for the application of the "ten-day rule" than that originally envisaged by the ICRP. Yours, etc.
(1973) and Spiers (1969). Both label the ordinate axis ratio of absorbed dose rather than ratio of ionization produced. Now under equilibrium conditions the ratio of absorbed dose in copper to absorbed dose in carbon is equal to the ratio of the mass energy absorption coefficients for the particular photon energy considered. In the case of y rays from 60 Co this ratio is equal to 0.92, using data obtained from Knipe (1975). This signifies that under equilibrium conditions the absorbed dose in the carbon is slightly greater than the absorbed dose in the copper. However, the graphs with relabelled ordinate axes predict this same ratio to be 1.46, i.e. they predict that under electronic equilibrium the absorbed dose in copper is 1.46 times the absorbed dose in carbon. Now, one of the aims of Dutreix and Bernard's article (1966) is to investigate the underdosage and overdosage of tissue in the transition zone between tissue and a metal surface. The mistake is therefore not a trivial one. R. SEAR. The following shows how the discrepancy can be resolved: Radioisotope Department, mSz Dz=k U—^-^rad (1) The London Hospital, mSair Whitechapel, London E1 1BB where Dz = absorbed dose in a volume element of material REFERENCES Z BRITISH INSTITUTE OF RADIOLOGY, 1975. Irradiation of U = ionization produced in the air ionization human subjects for medical research. BIR Bulletin 1, 2, chamber 4-6. k — conversion factor for absorbed dose in air, INTERNATIONAL COMMISSION ON RADIOLOGICAL PROTECTION. rad/R=0.869 Publication 9, 1966. Recommendations of the ICRP mSz _ mass stopping power ratio of material Z (Pergamon Press, Oxford). mSair relative to air. OSBORN, S. B., 1977. Restricted applicability of the "ten-day Dutreix et al. (1962) found that for y rays from 60Co and rule". British Journal of Radiology, 50, 606. for the situation studied, the mean energy of the electrons Report of a WHO/IAEA consultation on the use of ionizing which form the electron flux in the equilibrium state is ef the radiation on human beings for medical research and train- order of 10 keV. Thus the ratio of the mass stopping powers ing including the use of radioactive materials. November should be calculated for a mean electron energy of 10 keV. 6-10, 1972. (Geneva, Report WHO/RHL/73.1). ICRU Handbook 78 (1959) gives (table 8.6) stopping power Report of a working party of the MRC Isotope Advisory ratios for 60Co y rays as 1.02 and 0.68-0.75 for C/air, Cu/air Panel on the application of the "ten-day rule" in radio- respectively. Dutreix and Bernard found experimentally that pharmaceutical investigations. 1977. British Journal of the ratio of ionization in carbon to that in copper under Radiology, 50, 200-202. equilibrium conditions is 0.69. Using equation (1) and the SEAR, R., 1974. Radioisotopes and the "ten-day rule". stopping power ratios quoted, the ratio of absorbed dose in British Journal of Radiology, 47, 822. the carbon to that in the copper under equilibrium conditions is 0.97. This agrees well with the predicted value of 0.92 found from the ratio of the mass energy absorption coefficients. THE EDITOR—SIR, It is to be hoped that future reproductions of the results of INTERFACE DOSIMETRY The study of an article in the March 1966 issue of this Dutreix et al., will not contain this error. Yours, etc., Journal (Dutreix and Bernard, 1966) has brought to light an D. LOWE. error of translation that appears to have gone unnoticed. Effectively the article summarizes in English work on Department of Nuclear Science and Technology, interface dosimetry carried out at the Institut G. Roussy, Royal Naval Colege, Villejuif, France, and previously published in French in a Greenwich, London SE10. number of articles, viz: Dutreix et al. (1962), Dutreix et al. (1964), and Dutreix and Bernard (1965). REFERENCES Briefly, the authors made ionization measurements in the BURLIN, T. E., SIDWELL, J. M., and WHEATLEY, B. M., 1973. Applications of Monte Carlo methods in medical radiology vicinity of a carbon/metal interface irradiated by y rays British Journal of Radiology, 46, 398-399. from 60Co and X rays in the energy range 10 MV to 20 MV. These measurements made possible the determina- DUTREIX, J., DUTREIX, A., and BERNARD, M., 1962. Etude de tion of the dose absorbed by a water equivalent medium la dose au voisinage de l'interface entre deux mileux de (carbon) in contact with a body of higher atomic number. It composition atomique differente exposes aux rayonnewas found that in the neighbourhood of the interface there ment et du 60Co. Physics in Medicine and Biology, 7, was an extremely rapid variation of dose, characterized by 69-82. the occurrence of peaks at a distance of 20-40 mg/cm2 behind DUTREIX, J., DUTREIX, A., BERNARD, M., and BETHENCOURT, the interface. These distributions were represented graphicA., 1964. Etude de la dose au voisinage de l'interface entre ally; the ordinate axis was labelled the ratio of ionization deux milieux de composition atomique differente, exposes in material Z to the ionization in carbon in the region where a des RX de 11 a 20 MV. Annales de Radiologie, 7 (3-4), 233-241. electronic equilibrium is established — U/Uc in the originals. One of these plots was reprinted in Dutreix and Bernard DUTREIX, J., and BERNARD, M., 1965. Etude de flux des (1966) Fig. 1, p. 206), the only difference being that the electrons secondaires et de leur retrodiffusion. Applicaordinate axis was now labelled the ratio of absorbed dose in tion a la determination de l'ionisation a l'interface entre material Z to absorbed dose in water in electronic equilibdeux milieux differents exposes a des RX de haute rium conditions—D/De. The assumption was made, thereenergie. Biophysik 2,179—192. fore, that U/Uc=D/De. I have found reproductions of this 1966. Dosimetry at interfaces for high energy X and selfsame graph in two other publications, viz: Burlin et al. gamma rays. British Journal of Radiology, 39, 205-210.
60
JANUARY
1978
Correspondence ICRU, 1959. Report of the International Commission on Radiological Units and Measurements. National Bureau of Standards (U.S.) Handbook 78. KNIPE, A. D., 1975. A revision of photon interaction data in the UKAEA nuclear data library. AEEW-M1368. SPIERS, F. W., 1969. Transition Zone Dosimetry. In Radiation Dosimetry, Ed. F. H. Attix, W. C. Roesch and E. Tochilin, Vol. Ill, pp. 809-867 (Academic Press, New York).
There has been correspondence in these columns recently about this topic (Farmer, 1976; Nicholson, 1976; Davies, 1977; Isherwood, 1977) but written from the rather different viewpoint of finding a name to describe and distinguish between X-ray transmission section scans, and radioisotope emission section scans. It seems to us that the problem is really much wider than this. Confusion may be caused by names based on initials (for example, TCAT and ECAT for transmission and emission computerized axial tomographs) which are only really understood by the "inner clique"; or new uses of the classical languages, which are often obscure to the uninitiated (e.g. zeugmatography for nuclear magnetic resonance imaging); or upon commercial names (e.g. EMI scan) which will not apply in a hospital with a machine of another manufacturer. It would be better to concentrate on combinations of commonly used and accepted names of any reasonable origin. This is more likely to be acceptable and come into common parlance, thereby clarifying the confusion. Yours, etc.,
THE EDITOR—SIR, NOMENCLATURE IN SCANNING INVESTIGATION
Since radioisotope (or radionuclide!) investigations are no longer unique in having a "scanning" procedure, the term has now become ambiguous. In-patients who have left the ward "to go for a scan" are becoming increasingly difficult to trace. In Aberdeen there are separate locations for gamma camera studies, rectilinear scanning, in vivo uptake tests and whole body counting, ultrasonic and thermographic studies, and X-ray cerebral scanning (EMI scanner). While the efficiency of having one word for one investigation is admirable, we really ought to be qualifying the word "scan" as a routine or else abandoning it altogether. Since there is little hope of abandoning it, the simplest solution is for the people who perform the investigations to be more specific in their terminology and make the effort of saying radioisotope scan, X-ray scan, ultrasound scan or thermal scan. Within each category again simple but specific terminology would keep everyone informed for example, with radioisotope scans there are conventional views and tomographic or section views. The important thing is to establish a working terminology which everyone in the hospital will understand and use in the interest of the patient.
W. I. KEYES, J. R. MALLARD.
Department of Medical Physics, University of Aberdeen, Foresterhill, Aberdeen AB9 2ZD REFERENCES DAVIES, E. R., 1977. Computerized tomographic scan terminology. British Journal of Radiology, 50, 77. FARMER, F. T., 1976. Terminology in computerized imaging. British Journal of Radiology, 49, 815. ISHERWOOD, I., 1977. Computerized tomographic scan terminology. British Journal of Radiology, 50, 374. NICHOLSON, J. P., 1976. New terminology needed. British Journal of Radiology, 49, 653.
61
