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Shielding for radioisotope bremsstrahlung sources Sr90 + Y90
Technical notes International Journal of Applied Radiation and Isotopes, 19fi5, Vol. 16, p. 613. Pergamon Press Ltd. Printed in Northern Ireland
A Technetium-99m
Labeled
Colloid
(Received 28 February 1965)
Introduction Six-hour Tcggm has been recently(1-3) proposed as a tracer for medical diagnosis. This isotope can easily be “milked” as TcggmO, by 0.1 N hydrochloric acid or isotonic sodium chloride solution, from an alumina column containing 67-hr Mogg. Moreover, its single low energy (0.140 MeV) y-ray makes it especially suitable for scintillation scanning. HARPER et al.(*p3) use for liver scanning a Tcsgm colloidal preparation, probably TcsS, absorbed on colloidal sulphur. They preparet4) this colloidal solution by bubbling hydrogen sulphide through an acid solution of gelatine containing Tcggm, and purifying it from free TcO,by ion exchange resin. We have studied a simple preparation procedure, which the user can perform by very short chemical manipulations before the injection. We have found that a labeled colloid can be prepared adding to preformed colloidal antimony sulphide, free from hydrogen sulphide and stabilized with polivinylpyrrolidone (PVP), an equivalent volume of the saline solution containing the “milked” Tcgsm. This preparation was sterilized by autoclave heating for 30 min at 120°C. Further purification proved to be unnecessary because, after this treatment, the colloidal particles retain the Tcggnl quantitatively. In this way the preformed colloid, supplied to the user, can easily be labeled shortly before injection. \1’e have obtained clear liver scannings by intravenous injection of the colloid to rabbits. DECROSSI rt uZ.(j) have used the same preparation in men with good results.
Experimental ‘rcogm04- was “milked” from Mogg by elution with isotonic saline solution. The preparation of the antimony sulphide was carried out by the classical procedure, adding 20 ml 176 antimony potassium tartrate to 100 ml boiling distilled water, saturated with hydrogen sulphide. :2fter stabilizing with 10 ml 6% PVP solution, the Fxcess hydrogen sulphide was carefully removed with nitrogen. The preparation was sterilized, heating for 30 min at 120°C. The preformed colloid is extremely stable for more than 3 months. The investigation of labeling yield was performed by adding, to 5 ml colloid, different amounts of Tcggn,04saline solution and subsequent autoclave heating for 30 min at 120°C.
613
Under these conditions, for ratios of theTcggm solution volume to the preformed colloid volume up to 1, the yield was better than 98%. We have found that the heating process increases the labeling yield. Furthermore we have observed that in preparing the TcsS, colloid according to the procedure described by HARPER et al., the yield is about 70%. However, if the preparation is heated for 30 min at 12O”C, after having bubbled hydrogen sulphide through the Tcsgn solution, the yield increases to 100%. This makes unnecessary the purification step by exchange resin. All the studies of the labeling yield and the determinations of free Tcsgnz were carried out by dialysis. The particle size was determined by ultrafiltration, 15-20% of them having a diameter smaller than 100 mp, the remainder a diameter of 100-200 m,u. The toxicity of the colloidal antimony sulphide was investigated by intravenous injection of antimony sulphide to mice (0.17 mg) and rabbits (8.4 mg). No toxicity reactions were observed. 0. L. GARZ~N M. C. PALCOS R.
RADICELLA
Comisidn National de Energia Atdmica Buenos Aires, Argentina
References 1.
HARPER
P. V. et al. Chicago Clinical Society i2lreting,
April (1962). 2. HARPER P. V. et al. Nucleonics 22, (1) 50 (1964). 3. LATHROP K. A. and HARPER P. V. Second Annunl Oak Ridge Radioisoto&es Conference, April (1964). 4. HARPER P. V. et al. J. Nucl. Med. 5, 382 (1964). 5. DEGROSSI 0. e.tal. Nature, Lond. In press.
International Journal of Applied Radiation and Isotopes, 1965, Vol. 16, pp. 613-615. Pergamon Press Ltd. Printed in Northern Ireland
Shielding for Radioisotope Bremsstrahlung Sources SrgO+ Ygo (Received 26 February 1965) IN A recent paper FLORKOWSKI(~) has compared the attenuation factors in lead, for the radiation from a SrgO bremsstrahlungsource, determined by experiment with values which he has deduced theoretically using the following assumptions: (i) That only the Yg’J component of the source contributes substantially to the bremsstrahlung. (ii) The energy distribution of the bremsstrahlung is analogous to that calculated by WYARD(~) for P32. (iii) This bremsstrahlung spectrum
614
Technical notes
L
IOOcm-
thickness of lead was extrapolated from the experimentally derived attenuation curve. We have also determined the attenuation curves in lead for a bremsstrahlung source of SrgO !- Ygo (Type Buchlcr, VZ 0059, transmission target 0.05 mm Pt, backscatter target 0.4 mm I’t, coated by 0.2 mm Ni 1, These measurements were made to obtain racliatioll protection datas for thickness gauges manufacturctl by our organization. ‘I’he specific y-ray constant for the bremsstrahlung of these sources was T - 0.012 r m” hr~‘c-l. ‘I‘hC generation of bremsstrahlung is strongly inlluencetl by the construction of the source and the indicntcd value is only valuable for sources of the same design. The bremsstrahlung source (Fig. 1) is embrdcled in a lead block and covered with a 3 mm ,\I plate so that the p-rays arc completely absorbed. ‘l’his /:shielding is flush-mounted on the lead block. ‘i‘lrc, absorption layers, 100 x 100 mm, are placed directl) in front of the lead block. ‘The measurements conformed with “broad-beam geometry” and the distance between the source and the detector was 100 cm. The detector was an ionization chamber with th(, following characteristics: chamber volumr 5000 CI~:~. air-filled: wall l-2 mm polyethylcnc lined \vith graphite: radiation window 200 mm diameter ,\Icoated Hestaphan film 3.6 mg/cm”, for c.lcctron compensation a layer of 3 mm Al was placed in front of the window. L$‘ith this layer, electron equilibrium was obtained even for bremsstrahlung with c.nrrgich equal to the maximum /I-energy of Yg”. ()n the othc.1.
-
FIG. 1. Diagram to show the construction of the bremsstrahlung source and the arrangement of the detector. 1. Lead block of wall thickness 15 cm with a 5 cm x 5 cm cavity; 2. Sr”O-YgO source, diameter 22 mm; 3. Al plate 3 mm thick; 4. Lead absorber; 5. Ionization chamber; 6. Vibrating condenser electrometer. is divided into ten intervals and for any interval, after evaluating the specific y-ray constants and the absorption coefficients for lead, the exposure dose rate contributions are summed up to the total exposure dose rate behind lead layers of given thickness. The experimental values of the attenuation factors were determined by means of Geiger counters which In the series of were calibrated with a Ra-source. measurements only lead thicknesses over 0.5 mm were considered, and the exposure dose rate for zero
Attenuotnn
factors of
for
bremsstrahlung
Sr90+Y90
FLORKOWSKI
Lead
thickness
_
FIO. 2. Comparison of the attenuation factors measured with the ionization chamber with the theoretical and experimental values of FLORKOWSKI.
Technic al notes hand, the small selective absorption by 3 mm Al did not give rise to variations in the slope of the absorption curves beyond the limits of experimental error. The ionization current was measured with a I:rieseke & Hoepfner vibrating condenser amplifier ‘l’ype FH 56. The results are compared with those of FLORKOWSKI in Fig. 2. The error in our measurements was estimated to be +5 per cent. Our experimental values show better agreement with the theoretical values of FLORKOWSKI than his experimental results. This is due mainly to the fact that our testing method was more suitable for exposure-dose measurements. In the range of lead thickness over 1 cm our absorption curve lies approximately 20 per cent below the theoretical curve of FLORKOWSKI; this might be due to the fact that FLORKOWSKI omitted to take account of the K-radiation which, according to the published spectra(lV3) contributes about 20 per cent to the
615
radiation intensity. This and the emission of the bremsstrahlung of SrgO might be the reason for the steeper rise of our curves. In fact, the agreement between our results and the theoretical curve of FLORKO~SKI is satisfactory so that the method employed by FLORKOWSKI can well be used for other bremsstrahlung shielding problems. H. H. NAUMANN Frieseke and Hoepfer GmbH. K. H. WAECHTER Erlangen-Bruck, Germany References Rad. Isotopes 15, 579 1. FL~RKOWSKI T. Int. J. a#. (1964). 2. WYARD S. J. Nucleonics 13 (7) 44 (1955). Ausgabe A82, 372 3. WAECHTER K. H. E.T.Z. (1961).
A Technetium-99m
Labeled
Colloid
(Received 28 February 1965)
Introduction Six-hour Tcggm has been recently(1-3) proposed as a tracer for medical diagnosis. This isotope can easily be “milked” as TcggmO, by 0.1 N hydrochloric acid or isotonic sodium chloride solution, from an alumina column containing 67-hr Mogg. Moreover, its single low energy (0.140 MeV) y-ray makes it especially suitable for scintillation scanning. HARPER et al.(*p3) use for liver scanning a Tcsgm colloidal preparation, probably TcsS, absorbed on colloidal sulphur. They preparet4) this colloidal solution by bubbling hydrogen sulphide through an acid solution of gelatine containing Tcggm, and purifying it from free TcO,by ion exchange resin. We have studied a simple preparation procedure, which the user can perform by very short chemical manipulations before the injection. We have found that a labeled colloid can be prepared adding to preformed colloidal antimony sulphide, free from hydrogen sulphide and stabilized with polivinylpyrrolidone (PVP), an equivalent volume of the saline solution containing the “milked” Tcgsm. This preparation was sterilized by autoclave heating for 30 min at 120°C. Further purification proved to be unnecessary because, after this treatment, the colloidal particles retain the Tcggnl quantitatively. In this way the preformed colloid, supplied to the user, can easily be labeled shortly before injection. \1’e have obtained clear liver scannings by intravenous injection of the colloid to rabbits. DECROSSI rt uZ.(j) have used the same preparation in men with good results.
Experimental ‘rcogm04- was “milked” from Mogg by elution with isotonic saline solution. The preparation of the antimony sulphide was carried out by the classical procedure, adding 20 ml 176 antimony potassium tartrate to 100 ml boiling distilled water, saturated with hydrogen sulphide. :2fter stabilizing with 10 ml 6% PVP solution, the Fxcess hydrogen sulphide was carefully removed with nitrogen. The preparation was sterilized, heating for 30 min at 120°C. The preformed colloid is extremely stable for more than 3 months. The investigation of labeling yield was performed by adding, to 5 ml colloid, different amounts of Tcggn,04saline solution and subsequent autoclave heating for 30 min at 120°C.
613
Under these conditions, for ratios of theTcggm solution volume to the preformed colloid volume up to 1, the yield was better than 98%. We have found that the heating process increases the labeling yield. Furthermore we have observed that in preparing the TcsS, colloid according to the procedure described by HARPER et al., the yield is about 70%. However, if the preparation is heated for 30 min at 12O”C, after having bubbled hydrogen sulphide through the Tcsgn solution, the yield increases to 100%. This makes unnecessary the purification step by exchange resin. All the studies of the labeling yield and the determinations of free Tcsgnz were carried out by dialysis. The particle size was determined by ultrafiltration, 15-20% of them having a diameter smaller than 100 mp, the remainder a diameter of 100-200 m,u. The toxicity of the colloidal antimony sulphide was investigated by intravenous injection of antimony sulphide to mice (0.17 mg) and rabbits (8.4 mg). No toxicity reactions were observed. 0. L. GARZ~N M. C. PALCOS R.
RADICELLA
Comisidn National de Energia Atdmica Buenos Aires, Argentina
References 1.
HARPER
P. V. et al. Chicago Clinical Society i2lreting,
April (1962). 2. HARPER P. V. et al. Nucleonics 22, (1) 50 (1964). 3. LATHROP K. A. and HARPER P. V. Second Annunl Oak Ridge Radioisoto&es Conference, April (1964). 4. HARPER P. V. et al. J. Nucl. Med. 5, 382 (1964). 5. DEGROSSI 0. e.tal. Nature, Lond. In press.
International Journal of Applied Radiation and Isotopes, 1965, Vol. 16, pp. 613-615. Pergamon Press Ltd. Printed in Northern Ireland
Shielding for Radioisotope Bremsstrahlung Sources SrgO+ Ygo (Received 26 February 1965) IN A recent paper FLORKOWSKI(~) has compared the attenuation factors in lead, for the radiation from a SrgO bremsstrahlungsource, determined by experiment with values which he has deduced theoretically using the following assumptions: (i) That only the Yg’J component of the source contributes substantially to the bremsstrahlung. (ii) The energy distribution of the bremsstrahlung is analogous to that calculated by WYARD(~) for P32. (iii) This bremsstrahlung spectrum
614
Technical notes
L
IOOcm-
thickness of lead was extrapolated from the experimentally derived attenuation curve. We have also determined the attenuation curves in lead for a bremsstrahlung source of SrgO !- Ygo (Type Buchlcr, VZ 0059, transmission target 0.05 mm Pt, backscatter target 0.4 mm I’t, coated by 0.2 mm Ni 1, These measurements were made to obtain racliatioll protection datas for thickness gauges manufacturctl by our organization. ‘I’he specific y-ray constant for the bremsstrahlung of these sources was T - 0.012 r m” hr~‘c-l. ‘I‘hC generation of bremsstrahlung is strongly inlluencetl by the construction of the source and the indicntcd value is only valuable for sources of the same design. The bremsstrahlung source (Fig. 1) is embrdcled in a lead block and covered with a 3 mm ,\I plate so that the p-rays arc completely absorbed. ‘l’his /:shielding is flush-mounted on the lead block. ‘i‘lrc, absorption layers, 100 x 100 mm, are placed directl) in front of the lead block. ‘The measurements conformed with “broad-beam geometry” and the distance between the source and the detector was 100 cm. The detector was an ionization chamber with th(, following characteristics: chamber volumr 5000 CI~:~. air-filled: wall l-2 mm polyethylcnc lined \vith graphite: radiation window 200 mm diameter ,\Icoated Hestaphan film 3.6 mg/cm”, for c.lcctron compensation a layer of 3 mm Al was placed in front of the window. L$‘ith this layer, electron equilibrium was obtained even for bremsstrahlung with c.nrrgich equal to the maximum /I-energy of Yg”. ()n the othc.1.
-
FIG. 1. Diagram to show the construction of the bremsstrahlung source and the arrangement of the detector. 1. Lead block of wall thickness 15 cm with a 5 cm x 5 cm cavity; 2. Sr”O-YgO source, diameter 22 mm; 3. Al plate 3 mm thick; 4. Lead absorber; 5. Ionization chamber; 6. Vibrating condenser electrometer. is divided into ten intervals and for any interval, after evaluating the specific y-ray constants and the absorption coefficients for lead, the exposure dose rate contributions are summed up to the total exposure dose rate behind lead layers of given thickness. The experimental values of the attenuation factors were determined by means of Geiger counters which In the series of were calibrated with a Ra-source. measurements only lead thicknesses over 0.5 mm were considered, and the exposure dose rate for zero
Attenuotnn
factors of
for
bremsstrahlung
Sr90+Y90
FLORKOWSKI
Lead
thickness
_
FIO. 2. Comparison of the attenuation factors measured with the ionization chamber with the theoretical and experimental values of FLORKOWSKI.
Technic al notes hand, the small selective absorption by 3 mm Al did not give rise to variations in the slope of the absorption curves beyond the limits of experimental error. The ionization current was measured with a I:rieseke & Hoepfner vibrating condenser amplifier ‘l’ype FH 56. The results are compared with those of FLORKOWSKI in Fig. 2. The error in our measurements was estimated to be +5 per cent. Our experimental values show better agreement with the theoretical values of FLORKOWSKI than his experimental results. This is due mainly to the fact that our testing method was more suitable for exposure-dose measurements. In the range of lead thickness over 1 cm our absorption curve lies approximately 20 per cent below the theoretical curve of FLORKOWSKI; this might be due to the fact that FLORKOWSKI omitted to take account of the K-radiation which, according to the published spectra(lV3) contributes about 20 per cent to the
615
radiation intensity. This and the emission of the bremsstrahlung of SrgO might be the reason for the steeper rise of our curves. In fact, the agreement between our results and the theoretical curve of FLORKO~SKI is satisfactory so that the method employed by FLORKOWSKI can well be used for other bremsstrahlung shielding problems. H. H. NAUMANN Frieseke and Hoepfer GmbH. K. H. WAECHTER Erlangen-Bruck, Germany References Rad. Isotopes 15, 579 1. FL~RKOWSKI T. Int. J. a#. (1964). 2. WYARD S. J. Nucleonics 13 (7) 44 (1955). Ausgabe A82, 372 3. WAECHTER K. H. E.T.Z. (1961).