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A versatile radium storage safe

This content has been downloaded from IOPscience. Please scroll down to see the full text. 1978 Phys. Med. Biol. 23 986 (http://iopscience.iop.org/0031-9155/23/5/017) View the table of contents for this issue, or go to the journal homepage for more

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PHYS. MED. BIOL., 1978, Vol. 23, S o . 5, 986-988.

Printed in Great Britain

Technical Note

A Versatile Radium Storage Safe C. J. KARZMARK,

PH.D.

and P. A. HUISMAN,

D.ENGR.

Department of Radiology, Stanford University School of Medicine, Stanford, CA 94305, U.S.A.

Received 21 February 1978

Theradium safe described provides secure, conveniently supervised and monitored storage for more than 200 radium needles and tubes (500 mg) and is adaptable for storing other brachytherapy radionuclides. Distinctive features of the safe are: (1) the light-weight, rotating drum which holds the sources, (2) the ease, safety and rapiditywith which sources can be inventoried, removed or returned to the safe, and (3) a port through which radon leak tests can be made with minimal exposure to radiation. Thegeometry of the safe is cylindrical. Alight-weightaluminiumdrum houses 24 source holders and rotates about a vertical axis within stationary lead shielding. Fig. 1 shows a vertical assembly section of the safe, a view of the rotating drum housing the 24 source holders and the source holder details. We have found this design less troublesome mechanically compared to the linear drawer geometryof an earlier safe, thereby reducing personnel exposure. The safe weighs approximately 550 kg; thecylindrical body is 50 cm in diameter, 32 cm in height (fig. 2). It is secured to a wall, and supported at bench height from the floor on a 5 cm pipe and an overhead anchor bolt facilitates installation with block and tackle. No malfunction has occurred during more than seven years of use. Presently, it is used for storing radium needles and tubes, but can be used for the storage of I3'Cs or 6oCobrachytherapy sources as well. However, this would require modification of the source holders and a reassessment of the shielding requirements. The construction and operation of the safe are described in terms of the components identified in fig. 1. Six major sub-units identified in fig. 1 are: I, the source holder ; 11,the rotating drum; 111,the lead-filled base ; IV, thelead-filled cover; V, a light-weight cover housing mechanical components; and VI, the mirror-light assembly. Each source holder is 2.2 cm in diameter, 9 cm high, and is drilled to accommodate the requisite number and size of needles or tubes o f a particular typeto be stored (maximum of 12). As illustrated in fig. 1 , the sources protrude sufficiently for easy visualisation and access but are below the raised protectiverim(toprevent bending or shearing). Source holders remain in the lower position (solid outline in fig. 1)except when the sources are being removed or replaced (dashed upper outline). An important precaution, as in manysafes, is neverto attemptt'o return bent sources to thesource holder 0031-9155/78/0005-0986$01.00

@ 1978 The Institute of Physics

A Versatile Radium Storage Safe

987

since protrusion above the protectiverim may occur. This hazard is adequately described in the operatinginstructions and nosuchaccidenthas occurred. Furthermore, thelow mass of the drumminimises the torqueneeded for rotation and hence minimises the chances of damaging a source. Top vlew Posltion

Position correct

m m Pb Fe

AI

0 10 20 U Scale (cm)

Fig. 1. Vertical assembly section of safe, the rotating drum which houses the source holders and source holder details. I, source holder; 11, rotating drum; 111, leadfilled base; IV, lead-filled cover; V, cover; VI, mirror-light assembly; FP, flexible pusher; K,, rotating drum position indexing knob; K,, source holder updown knob; L, safe lock; 0, opening to remove and replace sources; T, tubes to radon gas detector; and W, window for drum index position indication. Source holder I is double scale for clarity. The top 0 off position in rotating drum I1 is shown filled with a blank lead source holder.

The 25 index positions are identified by numbers engraved on the top cap of the rotating drum and visible through window W. Source holders in index positions 1 to 24 may be used to house sources ; position 0, the off position, is filled with a removable lead blank cylinder. To remove a source, the key is inserted and lock L unlocked; this opens access opening 0, lights lamp VI and K, is then rotated to the approreleases knob K, for rotation. Index knob priate source holder index position;the source holder I is pushed up toopening 0 by means of a flexible pusher cable FP with a half-turnclockwise rotation of K,. The mirror of assembly VI is adjusted for individual ease of viewing the sources and the requisite sources are then removed with long tweezers. Knob K, is then rotated one-half turn anti-clockwise, restoring source holder I to its lower restingposition.Theindexknob K, may then be rotated to a new source position or the 0 off position. At the 0 position, a turn of the key closes

988

A Versatile Radium Storage Safe

a door at opening 0, locks the safe and extinguishes light VI. Two mechanical interlocks coordinate the positions of drum index knob K, and knob K, in a safe manner. If a source up motion is initiated by knob K,, the index position knob K, cannot be moved. Alternatively, knob K, cannot be moved unless index knob K, is in one of the well defined index positions 1 to 24 inclusive. The key cannot be remored unless the safe is locked.

Fig. 2. Photograph of safe. Many of the components identified in fig. 1 may be seen in this photograph.

Tubes T allow leak testing of radium sources using any escaping radon gas. This isaccomplished automatically once every 24 hours by means of a one litre external ionisation chamber detector (Radium Leak Detector, RL-I, Johnson LaboratoriesInc., Cockeysville, MD 21030) capable of detecting 50 pCiof radon at a signal-to-noise ratio of ten to one (Waters 1969). For our 500 mg radium inventory and with thesafe locked, the dose rate on the surface of the safe varies from 10-40 mrad h-, falling to 2-3 mrad h-l at a distance of 30 cm. A maximum dose rate of 40 mrad h-l at 30 cm occurs with the safe unlocked and a source holder containing 90 mg placed in the upposition. Wewish t o acknowledge the help of our colleagues, Bernice Palos and Roland Finston, in the preparationof this report. This work has been supported by Research Grant CA 05838 from the National Cancer Institute, N.I.H. REFERENCE WATERS,JOHN R., 1969, Health Phys., 16, 379.

A versatile radium storage safe.

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