US3588031A - Internally shielded teletherapy source - Google Patents

Internally shielded teletherapy source Download PDF

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Publication number
US3588031A
US3588031A US793699*A US3588031DA US3588031A US 3588031 A US3588031 A US 3588031A US 3588031D A US3588031D A US 3588031DA US 3588031 A US3588031 A US 3588031A
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United States
Prior art keywords
source
teletherapy
cobalt
radiation
shielding
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Expired - Lifetime
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US793699*A
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English (en)
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Norman C Howard
Lawrence E Wilkinson
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General Electric Co
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General Electric Co
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    • G—PHYSICS
    • G21—NUCLEAR PHYSICS; NUCLEAR ENGINEERING
    • G21F—PROTECTION AGAINST X-RADIATION, GAMMA RADIATION, CORPUSCULAR RADIATION OR PARTICLE BOMBARDMENT; TREATING RADIOACTIVELY CONTAMINATED MATERIAL; DECONTAMINATION ARRANGEMENTS THEREFOR
    • G21F5/00—Transportable or portable shielded containers
    • G21F5/02—Transportable or portable shielded containers with provision for restricted exposure of a radiation source within the container
    • A—HUMAN NECESSITIES
    • A61—MEDICAL OR VETERINARY SCIENCE; HYGIENE
    • A61N—ELECTROTHERAPY; MAGNETOTHERAPY; RADIATION THERAPY; ULTRASOUND THERAPY
    • A61N5/00—Radiation therapy
    • A61N5/10—X-ray therapy; Gamma-ray therapy; Particle-irradiation therapy

Definitions

  • the internal shield in intimate contact with the cobalt-60 has a wall thickness of from about 0.3 to about 0.7 centimeters and comprises uranium or tungsten metal or an alloy thereof.
  • This arrangement permits the use of higher activity cobalt loadings in standard teletherapy machines. Also, this permits more effective use of the radiation and more accurate and effective radiation therapy.
  • the object of externalbeam therapy is to produce a homogeneous distribution of absorbed energy within a prescribed treatment volume and time interval, while producing no energy absorption in the tissues outside this volume. It has been found that the higher the generating voltage, the more therapeutically useful are the characteristics of an X-ray beam for the treatment of deepseeded cancer. Thus, X-ray generators with ever higher voltages have been developed.
  • Cobalt-60 units are also advantageous over high voltage X- ray generators because of their simplicity, flexibility and constancy of output.
  • the absence of complicated electric and electronic circuits reduces maintenance problems and eliminates the need of a highly skilled maintenance staff.
  • the relative simplicity and small size of the source head and the absence of heavy electrical connections allow a high degree of flexibility in equipment design. This has resulted in the development and production of a wide range rotational cobalt- 60 units.
  • the radiation source used in the cobalt-60 teletherapy units consists of a small amount of cobalt-60 in a container which is inserted in the teletherapy head.
  • the usual cobalt-60 beam therapy unit consists of the encapsulated cobalt-60 radioactive source, a source shield or housing, a shutter device to turn the useful beam on and off and a variety of support mechanisms and beam control and adjustment mechanisms.
  • the source housing and shutter includes sufficient shielding material, such as lead, so that the leakage radiation from the source shield will average less than 2 milliroentgens per hour at a distance of one meter from the source in all directions. While a wide variety of therapy units have been designed, a single international standard source holder has been designed which will fit most of these units. This holder can accommodate a.
  • the quantity of shielding material included in the unit housing is determined by the radiation leakage limit and the expected activity of sources to be used therein.
  • higher output sources may not be usable in older teletherapy units since they would cause leakage radiation exceeding the permissible limits.
  • high-output source materials are now becoming available due to improved ability to produce cobalt-60 in high flux level nuclear reactors. High activity sources permit the treatment of a deep seated tissue in shorter periods.
  • the maximum source diameter is 3 centimeters.
  • smaller diameter sources may be used by inserting a spacer ring (or shim) between the outer wall of the source and the inner wall of the holder.
  • the source diameter approaches a true point source and a diaphragm is used between the source and the object receiving the radiation, radiation will fall off sharply at the edge of the field.
  • a large penumbra will result; that is, the radiation falloff outside the field will be more gradual. This results from the fact that radiation coming from one side of the source is limited by the diaphragm aperture in a different way than that emerging from the opposite side. An extensive penumbra is undesirable since it will result in the irradiation of healthy and possibly sensitive tissues adjacent the portion being treated.
  • Another object of this invention is to provide a cobalt-60 teletherapy source permitting the use of higher output sources in existing machines.
  • Still another object of this invention is to provide a teletherapy source permitting a more precise radiation beam.
  • Still another object of this invention is to provide a teletherapy source of improved convenience, reliability and safety.
  • cobalt-60 teletherapy source in which the cobalt-60 source material is at least partially surrounded by and in intimate contact with a quantity of shield material which is in turn doubly encapsulated in stainless steel containers, the outside dimension of which fits within the international standard teletherapy source holder.
  • the cobalt- 60 material is in the form of small pellets in a generally cylindrical array within a ring, ringand-cap, or cup-shaped shield member.
  • the radial walls of said shield member preferably have a thickness of from about 0.3 to about 0.7 centimeters.
  • This thickness range is preferred since much thinner walls tend to decrease the shielding capability to the point where higher output cobalt- 60 sources cannot be safely used while much thicker walls would decrease the diameter of the core to the point where unachievably high specific activity would be required in the source material.
  • the internal shield member and source material are then doubly encapsulated in stainless steel cans having a thickness of about 0.65 millimeters.
  • Stainless steel is preferred for the encapsulating cans because of its strength, corrosion resistance and ability to be easily closed with high integrity welds. it is undesirable to use a high-density material for the encapsulating container, since this would also attenuate the radiation in the treatment beam.
  • uranium While any material having a density greater than about grams per cubic centimeter would be useful in the internal shield member, unalloyed and unclad uranium metal or a suitable tungsten alloy are preferred for use in the internal shield. Uranium performs extremely well as the internal shield. Preferably, the uranium is unalloyed and unclad since any alloying or cladding materials would have lower densities and would decrease the shielding ability of the internal shield member. Applicants'have found that uranium in the unclad state may be used in the configuration of this invention since the internal shield material is entirely encapsulated.
  • Uranium metal is difficult to use in an external shield in air since it is easily oxidized and then expands in volume, Thus, an external uranium shield may expand to the point where it prevents disassembly of close-fitting components.
  • Tungsten is also preferred for the internal shield material because of its high density and its availability at reasonable cost.
  • the addition of the internal shield member made up of very effective shielding material in intimate contact with the source material is much more effective than the equivalent quantity of shielding material spaced further from the source material.
  • the mass of shielding material to give an equivalent shield thickness is smaller where the shield is contained within the source material encapsulating cans than where the shield material is in the form of a ring outside the encapsulating cans.
  • the larger external shield ring would permit a greater quantity of radiation to leak out of the ends of the ring. Where the shielding is internal, the end leakage beams are significantly narrower.
  • the thickness of an absorber which attenuates a beam of radiation by one-half is called the halfvalue thickness.
  • the halfvalue thickness of uranium is 0.566 centimeters and of tungsten is 0.69 centimeters.
  • the inclusion of a 0.3 to 0.7 centimeter internal shield of uranium in a source capsule will increase the effective shielding of the overall unit by a factor of about 0.53 to 1.25. For tungsten this factor is about 0.43 to 1.02.
  • the permissible activity level of the source in a conventional teletherapy machine will be increased by from about 40 percent to about 125 percent.
  • the source may be made narrow er in order to approach more nearly to the ideal point source. This will greatly decrease the penumbra effect and substantially decrease the undesired irradiation of sensitive structures adjacent to the matter being irradiated.
  • FIG. 1 shows an isometric view, partly cut away, of a teletherapy source according to this invention positioned in an international standard source holder;
  • FIG. 2 shows an isometric view, partially cut away, of a second embodiment of the teletherapy source of this invention positioned in an international standard source holder;
  • FIG. 3 shows a schematic representation of a typical cobalt- 60 teletherapy machine including the teletherapy source of this invention.
  • FIG. 1 there is seen a teletherapy source generally designated 10 enclosed within an international standard source holder generally designated 11.
  • the dimensions of source holder 11 have been made standard by international agreement.
  • Source holder 11 carries external threads 12 to permit the source holder to be threaded into a teletherapy machine.
  • Source holder 11 is loaded by inserting thecylindrical source 10 into the standard diameter bore of source holder 11.
  • An annular inwardly projecting lip 13 prevents source 10 passing through the bore.
  • a retaining ring 14 engaged in an annular slot in the bore of source holder 11 retains source 10 in position.
  • source 10 consists of a quantity of cobalt- 60 source material 15 within a ring-shaped internal shield member 16 both of which are doubly encapsulated within two concentric stainless steel cans l7 and 1.8.
  • the end members of cans 16 and 17 are welded in place to prevent leakage of radioactive material.
  • This configuration permits the use of a high-activity cobalt- 60 source material in a standard teletherapy machine since additional shielding material is provided in the most effective location. Also, the cylinder of cobalt-60 source material is rela tively narrow thus decreasing the exit beam diameter and, therefore, the undesirable penumbra efiect. Since the internal shielding material 16 is entirely enclosed within double-encapsulating cans 17 and 18, materials such as uranium metal which tend to swell when exposed to the atmosphere may be used without inconvenience.
  • FIG. 2 shows a second embodiment of the teletherapy source of this invention.
  • the source 10 is retained between a lip 13 and a retaining ring 14 within the international standard source holder 1 1.
  • the internal shield member 16' has a generally cylindrical ringand-cap or cup-shaped configurationrather than the ringshape shown in FIG. 1.
  • the configuration shown in FIG. 2 will be preferred where source activity is very high.
  • the internal shield member 16 provides additional shielding both at the sides of source material 15 and at the back of the source. Of course, shielding in the beam port region would be undesirable since this would interfere with the use of the source in irradiating objects.
  • the portion of source material at the end of the source material cylinder away from the beam port will tend to be self-shielded by the source material closer to the beam port. Therefore, adding additional shielding material in the form of a cap or cup base at the back of the source in place of a portion of source material will not significantly decrease the effectiveness of a very high-activity source material while significantly increasing the shield effectiveness in this direction.
  • FIG. 3 shows a schematic representation of a typical teletherapy machine in which the teletherapy source of this invention is especially useful.
  • the teletherapy head generally designated is positioned above the object 21 to be irradiated on any conventional supporting structure (not shown).
  • a generally cylindrical shutter drum 22 is positioned in a horizontal cylindrical opening throughhead 20.
  • Drum 22 is rotatable by a drive means 23.
  • Adjacent one edge of drum 22 is a horizontal opening within which source drawer 24 is slidably inserted.
  • Drawer 24! is held in place by a removable end cover 25.
  • the teletherapy source in source holder 11 may be directly inserted into a cavity in drawer 24, or the cavity may be sized and threaded to receive teletherapy source in source holder 11 in source drawer 24.
  • Drive means 23 is capable of rotating drum 22 from an of! position as shown, in solid lines in FIG. 3, in which the source is surrounded by shielding material to an on position (shown in broken lines) in which the source in source holder 11 is adjacent a port 26 which permits radiation ofobject 21.
  • Collimating blocks 26 are provided to adjust the width of the irradiation beam, which is indicated by lines 27.
  • lines 27 As can be seen from FIG. 3, where the source in source holder 11 is a point source, line 17 will outline a sharp, distinct area on object 21. Where the source in source holder 11 has an appreciable source diameter, it is apparent that the edges of the area outlined by lines 27 will be vague and indistinct, thus making the treatment of a distinct zone on object 211 difficult.
  • a teletherapy source comprising:
  • cobalt- 60 source material has a specific activity of from about 300 to about 500 curies per gram.
  • each of said stainless steel containers has a wall thickness of about 0.65 millimeters.
  • shielding material is selected from the group consisting of unalloyed, unclad uranium metal and tungsten alloys.
  • a cobalt- 6O teletherapy source assembly comprising an annular international standard teletherapy source holder, secured within said holder a source capsule comprising a quantity of cobalt-60 teletherapy source material doubly encapsulated within stainless steel containers; the improvement wherein a quantity of a shielding material having a density greater than about 10 grams per cubic centimeter is provided between, said cobalt-60 source material and said encapsulating containers, said shielding material at least partially surrounding and in intimate contact with said source material.
  • said cobalt- 60 source material has a generally cylindrical configuration and said shielding material is in the form of a ring-shaped member surrounding and in intimate contact with said source material and in contact with the inner wall of the smaller of said encapsulating containers, said shielding material being selected from the group consisting of tungsten alloys and unalloyed, unclad uranium metal, said ring-shaped member having a wall thickness of from about 0.3 to about 0.7 centimeters.
  • said shielding material is generally cylindrical with an axial opening in one end filled with said cobalt-60 source material, said shielding being material selected from the group consisting of unclad, unalloyed uranium metal and tungsten alloys, said shielding material having a substantially uniform wall thickness in the range of from about 0.3 to about 0.7 centimeters.

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  • Physics & Mathematics (AREA)
  • Engineering & Computer Science (AREA)
  • General Engineering & Computer Science (AREA)
  • High Energy & Nuclear Physics (AREA)
  • Radiation-Therapy Devices (AREA)
  • Particle Accelerators (AREA)
  • Closures For Containers (AREA)
  • Physical Or Chemical Processes And Apparatus (AREA)
US793699*A 1969-01-24 1969-01-24 Internally shielded teletherapy source Expired - Lifetime US3588031A (en)

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US79369969A 1969-01-24 1969-01-24

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US (1) US3588031A (it)
JP (1) JPS5027157B1 (it)
BE (1) BE744894A (it)
CH (1) CH502826A (it)
DE (1) DE2002620B2 (it)
ES (1) ES375772A1 (it)
FR (1) FR2029069A1 (it)
GB (1) GB1286561A (it)
IT (1) IT954060B (it)
NL (1) NL7000413A (it)
SE (1) SE346047B (it)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4935943A (en) * 1984-08-30 1990-06-19 The United States Of America As Represented By The United States Department Of Energy Corrosion resistant storage container for radioactive material
US5442186A (en) * 1993-12-07 1995-08-15 Troxler Electronic Laboratories, Inc. Radioactive source re-encapsulation including scored outer jacket
DE202005019260U1 (de) * 2005-12-09 2007-04-19 RUHR-UNIVERSITäT BOCHUM Vorrichtung zum Aussenden ionisierender Strahlung
CN105031832A (zh) * 2015-08-27 2015-11-11 西安大医数码技术有限公司 适形调强放疗装置
US20160306069A1 (en) * 2013-03-20 2016-10-20 Geoservices Equipements Sas Radiation source device
CN107799195A (zh) * 2017-11-24 2018-03-13 北京新核医疗科技有限公司 水平中子束照射方法、微型堆中子治疗装置及医疗系统
CN111710457A (zh) * 2020-06-29 2020-09-25 北京三强核力辐射工程技术有限公司 一种全身伽玛刀放射治疗用钴-60放射源及其制备方法

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2992767B1 (fr) 2012-06-28 2014-08-08 Tn Int Emballage de transport et/ou d'entreposage de matiere radioactive
CN111477375B (zh) * 2020-04-29 2025-01-14 山东泉港辐射科技发展有限公司 一种源板架

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4935943A (en) * 1984-08-30 1990-06-19 The United States Of America As Represented By The United States Department Of Energy Corrosion resistant storage container for radioactive material
US5442186A (en) * 1993-12-07 1995-08-15 Troxler Electronic Laboratories, Inc. Radioactive source re-encapsulation including scored outer jacket
DE202005019260U1 (de) * 2005-12-09 2007-04-19 RUHR-UNIVERSITäT BOCHUM Vorrichtung zum Aussenden ionisierender Strahlung
US20160306069A1 (en) * 2013-03-20 2016-10-20 Geoservices Equipements Sas Radiation source device
CN105031832A (zh) * 2015-08-27 2015-11-11 西安大医数码技术有限公司 适形调强放疗装置
CN109107053A (zh) * 2015-08-27 2019-01-01 西安大医集团有限公司 适形调强放疗装置
CN107799195A (zh) * 2017-11-24 2018-03-13 北京新核医疗科技有限公司 水平中子束照射方法、微型堆中子治疗装置及医疗系统
CN107799195B (zh) * 2017-11-24 2024-01-09 北京新核核工程科技有限公司 水平中子束照射方法、微型堆中子治疗装置及医疗系统
CN111710457A (zh) * 2020-06-29 2020-09-25 北京三强核力辐射工程技术有限公司 一种全身伽玛刀放射治疗用钴-60放射源及其制备方法

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Publication number Publication date
NL7000413A (it) 1970-07-28
ES375772A1 (es) 1973-03-16
GB1286561A (en) 1972-08-23
DE2002620B2 (de) 1978-10-05
DE2002620A1 (de) 1970-07-30
SE346047B (it) 1972-06-19
CH502826A (de) 1971-02-15
IT954060B (it) 1973-08-30
FR2029069A1 (it) 1970-10-16
JPS5027157B1 (it) 1975-09-05
BE744894A (fr) 1970-07-23

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