Time reducing exposure containing 18 fluorine flourodeoxyglucose master vial dispensing in hot lab: Omega technique

INTRODUCTION

There is an indispensable need for containment of occupational and operational exposure to radiation.[1] The onus of responsibility to reduce exposure to the patient, occupational workers, and public largely rests on medical radiation workers who are the key personnel handling, dispensing, and using radioisotopes. Use of high activity packs of 18 fluorine fluorodeoxyglucose (18F-FDG) supplied by the cyclotrons in vials is the usual practice in hot labs. Individual doses are withdrawn and administered to patients by various practices which are not very much standardized. A novel technique has been devised to efficiently fractionate and dispense from the high dose master vials of F18-FDG. This technique is precise and less time-consuming with markedly reduced exposure to the personnel in the hot lab.

CONVENTIONAL 18 FLUORINE FLUORODEOXYGLUCOSE DISPENSING METHOD AND DRAWBACKS

Bulk doses of F18-FDG are supplied in sealed glass vials transported in suppliers’ lead/tungsten pigs with activities ranging from 50 to 200 mCi in volumes varying from 5 to 10 ml. At the hot lab, the vial is measured in dose calibrator for the activity supplied and transferred into the tungsten vial pig, which is conventionally tiltable and mounted on a steel frame. Individual doses are drawn with syringe and injected to the patients. This currently practiced procedure is besieged with a number of practical and operational complexities. The entire tilting pig with its stand is bulky and occupies a lot of space inside the lead well causing physical movement restraint. Movement of the vial inside the pig during insertion of the syringe needle and awkward angling of the wrist while inserting the syringe needle causes undue time delay, with increased radiation exposure to the wrists [Figure 1]. When the volumes in the vial are low as the last doses are reached, blind insertion of syringe needle most often results in the needle tip going above the fluid level resulting in air being withdrawn instead of the liquid. The air needs to be pushed back into the vial, the needle withdrawn a little to come below the fluid level to get the desired syringe fill. All these result in increased time duration of radioactivity handling and increased radiation exposure to the operator. Finally, despite the best efforts, some quantity of activity is always left behind in the vial after withdrawal of the last dose causing loss of usable activity for at least one more case. These set of practical and operational difficulties have necessitated designing of an innovative, time reducing exposure containing technique of FDG dispensing christened as Omega technique.

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Figure 1 Tilting master vial pig mounted on a stand and withdrawal using both hands

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NEW IMPROVISED 18 FLUORINE FLUORODEOXYGLUCOSE DISPENSING METHOD

Materials required

Tungsten pig, burette stand with clamps, small lead pot cut open on both ends, small lead pot lid with a slit cut, three-way cannula, 18-gauge sterile disposable lumbar puncture needle, and sterile saline loaded 5 ml syringe [Figure 2].

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Figure 2 Items required for newer method of fluorodeoxyglucose dispensing. (1) Burette stand, (2) small lead pot lid with a slit cut, (3) lead pot cut open on both ends, (4) bleeder needle, (5) lumbar puncture needle, (6) three-way cannula, and (7) saline loaded syringe

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Procedure

Step 1

Metallic burette stand is placed inside the lead well just behind the lead window, and the tungsten pig is then positioned vertically upward on its metal stand. Activity measured F18-FDG vial is placed inside the pig and lid closed, a sterile disposable lumbar puncture needle is inserted into the activity vial all the way till the bottom through the central hole of the tungsten pig lid [Figure 3a], and a vent needle inserted next to it for pressure equalization during withdrawl of liquid from the vial [Figure 3b].

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Figure 3 (a) Insertion of lumbar puncture needle (arrow) into the activity vial. (b) Vent needle (dotted arrow) insertion for pressure equalization

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Step 2

A sterile three-way cannula is attached to the hub of the lumbar puncture needle [Figure 4a] and the open-ended small lead pot threaded over it resting on the lid of the tungsten pig [Figure 4b]. It is then covered by the slit open lid with the three-way cock resting above it [Figure 5a], a sterile saline filled 5 ml syringe is clamped horizontally on the burette stem and its nozzle attached to the side hub of the three ways, and the second hub is facing upward [Figure 5b].

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Figure 4 (a) Three-way cannula (arrow) attached to the hub of the lumbar puncture needle. (b) Open-ended lead pot (dotted arrow) being threaded over the needles and three-way

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Figure 5 (a) Lead pot covered with slit opened lid (arrow). (b) Saline filled syringe clamped horizontally on the burette stem and attached to the three-way (dotted arrow)ab

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Step 3

The clamped syringe and needle attachments are all well stabilized and are movement free. A sterile empty syringe is attached to the vertical free hub of the three-way, the cock turned toward the master vial in the tungsten pig, the calculated volume of the activity is withdrawn [Figure 6a], the cock is then turned toward the saline syringe, and a small quantity of saline is withdrawn to ensure any activity within the hub also to be taken into the activity syringe [Figure 6b]. The three-way cock is now turned to all close position and the activity syringe withdrawn, measured in the dose calibrator, and taken for injecting to the patient. The same procedure is repeated for all the subsequent withdrawals till the complete activity in the master vial is exhausted. The dispensing unit is left as it is in the lead well till the next day when all the needles and three-way cannula are disposed off and new set of sterile disposables were used and the process was repeated.

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Figure 6 (a) Withdrawal from the activity vial with three-way cock turned toward activity vial side (vertical arrow). (b) Withdrawal of saline flush with three-way cock turned toward the side syringe (angled arrow)

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ADVANTAGES OF THE NEW TECHNIQUE

• Since the activity is withdrawn in a vertical position, fluid meniscus in the syringe is clearly visible

• Entry of air into the syringe is nil, as the needle is always below the fluid level and there is no scope of air in the vial mixing up with the liquid activity

• It takes only few seconds to complete the process of withdrawing the desired volume from the master vial with one hand only instead of two hands in the conventional method

• There is no chance of spillage or droplet of activity falling on the base as withdrawal position is vertical

• Even smallest volume of activity in the hub of the three-way is taken inside the activity syringe by the small saline flush integrated with the system

• The newer technique is very cheap and uses simple in-house available items and is faster

• Even the last drop of the activity is possible to be withdrawn by this technique, saving precious activity.

CONCLUSION

The newer method has a distinct advantage in terms of ease of operation, reduced time, and thus limiting radiation exposure to whole body and hands of the technologist. The technique effectively and efficiently masters the time component of radiation protection principles of time, distance, and shielding. The whole process is much faster than the conventional technique. The whole system is behind lead glass and lead shielding well placed far backward increasing distance component to the operator and thus further reducing exposure by the inverse square law principle. All this is achieved at no additional cost or cumbersome costly equipment.