ML20249C039
| ML20249C039 | |
| Person / Time | |
|---|---|
| Issue date: | 06/24/1998 |
| From: | Compton E NRC OFFICE OF NUCLEAR MATERIAL SAFETY & SAFEGUARDS (NMSS) |
| To: | Martone R PICKER INTERNATIONAL, INC. |
| Shared Package | |
| ML20249C040 | List: |
| References | |
| SSD, NUDOCS 9806250218 | |
| Download: ML20249C039 (22) | |
Text
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- k UNITED STATES j
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NUCLEAR REGULATORY COMMISSION f
WASHINGTON. D.C. 20$554001
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June 24, 1998 Ronald J. Martone Manager of Regulatory Compliance Picker InternationalInc.
Nuclear Medicing Division 595 Miner Road Highland Heights, OH 44143
Dear Mr. Martone:
Following a cursory review of the BEACON system, based on the design specifications included in your letter dated June 11,1998, we hope that the following suggestions may be helpful to the development of a future device application:
1.
Please r,ote that although the collimated be.am will remain in the confinement of the detectors, the NRC does not consider this an adequate safety measure in the event that a source could become stuck in an exposed position. What fail-safe measures are provided in cases of power failures or other problems in which the source may become stuck in an exposed position? One suggestion would be to include a retractable spring mounted to the inner cylinder, in which in the event of a power failure the i_nner cylinder would be retracted automatically into a shielded parked position under the tension of the spring. In addition, in the event of any unforseen computer " glitches" or other problems, cutting the power would be a sensible emergency procedure.
2.
In addition to N LED indicators or electronic sensors monitoring source status (i.e., parked, exposed), many manufacturers include some sort of mechanicalindicator for determining source position. LEDs or electronic sensors may not be one-hundred percent reliable, due to burn-outs or power failures. Also, the exact position of the source is not known with these components. Therefore, we suggest incorporating into the device a mechanical ruled indicator directly linked to the inner cylinder drive mechanism. This indicator should be easily visible without need for an operator to look into or bend over exposure regions.
3.
All moving parts, including the inner cylinder, should have adequate spacing to ensure they will not bind during use..One suggestion is to incorporate linear bearings into the inner cylinder to reduce binding at the guide rails and drive mechanism.
4.
' The NRC relies substantially on prototype testing to verify that the device will remain operational when subjected to conditions associated with normal handling and use, and will maintain its containment (e.g., no loss of byproduct material nor significant loss of shielding) with the necessary safety features remaining operable. Picker will need to demonstrate that the device will remain in its integrity after being subjected to repeated cycling and likely impacts during use.
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Cycle testing must demonstrate that the device will remain operational after the expected number of cycles over the years of use of the device. This can be accomplished by subjecting a prototype unit to the expected number of cycles a device may encounter during its useful life.
Picker may demonstrate the device will withstand likely impacts encountered during use.
The device does not need to remain operational after impact but there must not be a loss of radioactive material nor significant decrease in shieldingi This can be accomplished by subjecting a prototype unit to multiple drops onto a hard surface from
. the height of the device during normal use.
Please note that a complete application will need to be submitted before the NRC will begin a comprehensive review of the product. I have enclosed a copy of NUREG-1556, Vol. 3, containing information on preparing an application for a device evaluation. If you have any questions or need additional information, please contact me at (301) 415-5799 or Steven
' Baggett at (301) 415-7273.
Sincerely, b
Eric B. Compton, Engineering Aide Materials Safety Branch Division of industrial and Medical Nuclear Safety Office of Nuclear Material Safety and Safeguards
Enclosure:
NUREG-1556 Vol. 3 h
Distribution:
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l Beacon: A radiation protection perspective Differential (non-uniform) attenuation of the object to be imaged in nuclear medicine is one of the l
most important problems this technology is facing. The subject has received a lot of attention in the recent years and a patient-dependent attenuation map obtained by adding an extemal radioactive source to a standard gamma camera seems to be the optimal solution.
The proolem is further complicated by the fact that modem gamma cameras have to image both '
single photons in wide range of energy (typically 80 to 350 kev) and annihilation gamma of positron emitters at 511 kev.
Typically the low-energy transmission scanning was obtained by putting a 100 kev,9-month half.
life 23Gd source in either a fixed fan-beam geometry or in a scanning line source parallel beam configuration. Source strength were several tens of mci for the fixed geometry and several hundreds of mci for the scanning version. In the low energy application, a large portion of the radiation from the source is stopped by the collimator. In the high (511 kev) application, the source is typically the 30-year half-life,662 kev 137Cs used in the form of one of several point of several tens of mci. A large portion of the activity is lost by the poor efficiency of the detectors at those higher energies.
In a new approach, BEACON combines BOTH needs in one device with several cost, imaging and radiation protection advantages. This document summarizes the latter.
PARTI Presentation of the concept AXIS IRIX BEACON is an add-on option on the AXIS and IRIX product line. The AXIS /lRIX cameras are the first systems to be designed specifically with the high-energy requirements. Thicker crystal for better efficiency at higher energy and proper shielding for the detector are among the important design criteria. Another feature of the new product affecting the design of the extemalline source holder is the high degree of versatility of the gantry motion. It is a mandatory requirement that the source holder does not interfere with the gantry motions. The source holder was designed to retract into a safe position when not in use. The following series of figures help understanding the proposed concept.
Figure 1 presents the basic dual-head AXIS in 180* configuration with the source holder fully extended and ready to be used.
Figure 2 presents the AXIS in 90* mode suitable for quick 180* tomographic acquisitions with the source holder fully extended, p i e4 I'
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Figure 3 is a variation on Figure 2 presenting the AXIS in a 102* mode offering imaging advantages, especially for cardiac applications. Figure 2 also presents the source holder fully extended.
Figure 4 is a representation of the irising 3-detector IRIX system particularly well suited for brain imaging with the source holder completely retracted.
Figure 5 is a variation on Figure 4 and is showing an IRIX with two of the detectors in 102*
configuration and the source holder fully extended to do cardiac imaging.
l l
Source Geometry The source is iucated on the side of the field-of-view and is directeo Onto the opposite detector.
The source holder provides tight collimation in the axial direction, and elso restricts the beam in the transverse direction in such a way that only the area of the fan covering the largest possible area of the detector is covered. Area outside the active fan should be at (or close to) the background radiation level. Figures 6 and 7 are showing elements of the design.
Figure 6 presents the AXIS in 180 opposed configuration with the source holder fully extended in directed toward the opposite detector. The shaded area represents the active region.
Figure 7 shows the AXIS in 102* cardiac mode with the source holder fully extended and directed toward the other detector.
Outer Source Holder The description made so far only addresses the transverse plane (plane containing a section of the patient). However, the object (patient) needs to be scanned along the axial direction to be able to produce and 3D reconstruction. The axialinformation is generated by moving the radioactive point source (to be fully described below) along that direction. The source is located inside a cylinder that acts both as a mechanical guide and as a radiation shield. The whole cylinder is mounted on an arm and is manually retractable into the permanent housing mounted on the side of the detector bucket. A section of the cylinder does not have any opening and i, used to " park" the source in idle mode (source holder fully extended but not yet ready for imaging). In the park position, radiation from the source to either the patient, personnel or to the other detector should be minimal.
Figure 8 explains some of the mechanics of that design.
Figure 8 shows the complete source holder assembly with the movable parts and the storing section at both ends of the cylinder.
Inner Source Holder and Collimator
- The ' cylinder provides the mechanical guidance for the source and the secondary shielding. The inner source holder is designed to provide collimation and the primary shielding. The Inner Holder will surround the source and will have an opening providing enough angular range in the y 2.Z IL
r transverse plane to cover all the different geometry, and a small enough opening in the axial direction to provide accurate positioning on the opposite detector. " Shadow" of the source on the detector will effectively be used by the acquisition logic to window the event on '.he detector and L
accept only those events that are pertinent to the transmission information. Figure 9 to 11 are showing some of this design.
Figure 9 is showing the inner Source Holder in the transverse plane showing a 35*
opening large enough to cover all the gantry configurations. The longitudinal view shows the tight 2* collimation tunnel.
i Figure 101s showing the Source Assembly used to insert and secure the sealed source (from Isotope Froducts Inc) into the Source Holder.
Figure 11 presents in a 3D rendition the combination of the inner and the Outer Source Holder in a typical configuration establishing that the active plane is " contained" within a volume defined by the 2 (or 3) detectors.
Isotope Energy The selection of the isotope is the last major element in the design. The energy of the gamma rays was selected to meet several criteria. First, one source for the low and for the high energy application. Second, low energy sources (like 153Gd in previous design) are notoriously poor when used with larger patient making even more acute the problem of poor statistics by blocking a larger portion of the gamma. Third, since the gantry can be put in several different configurations, the geometry of the sources cannot be linked to the geometry of the collimator for single photon emission imaging, Therefore, a high enough gamma energy should be used to
- punch through" the collimators and provide the same information. However, a gamma ray energy which is very high is not desirable because of the associated radiation leakage. For all those reasons,350 to 400 kev range was selected.
Half-life The last step was the actual selection of the isotope. Several candidates were still available.1311 was rejected for short half life and difficulty in its manipulation.152Eu was rejected for cost and contaminants.133Ba was finally selected with 10.7 year half-life, all mechanical components can be for a permanent design (with expert personnel access only). This simplifies the design but also eliminate ALL user manipulation.. It is even likely that the source will be good for the whole life of the instrument.
Activity
- Because of the high accuracy of the scanning device and the precision of the collimation, a high
. quality image can be obtained with a very low activity. The specified activity will be around 10 mci per source,2 sources per camera.
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Radiation Protection issues j
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Advantages I
i The new design using a scanning medium energy point source within a retractable cylinder offers several advantages when compared to currently available product aiming at producing similar results. In no particular order:
- No user manipulation for the life of the equipment.
- Active area contained within a plane itself contained into a volume formed by the detector buckets themselves shielded for high energy imaging.
- Built-in park areas with additional shielding.
- Built-in permanent storage with additional shielding.
- Low activity.
- No user-fillable source option.
- Better image statistics for larger patient where increased imaging time (and exposure) was the only altemative.
Normal Operation in normal operation, the source will inside the inner Source Holder at one end of the cylinder in the park position. The opening of the cylinder will be facing the detector bucket so all radiation leaking from the Inner Source Holder will be contained in tha Outer Cylinder and all the radiation leaking out of the Cylinder will be blocked by the lead of the detector bucket. A green LED will clearly indicate that the source is in proper location.
The system will interpret a request for transmission as follow.
- Move the detector (s) at the appropriate angle and position according to the imaging type requested
- Release the arm mechanism holding the Outer Cylinder assembly
- The user will be asked through messages on the computer screen to manua!!y position the cylinder in a position in conformance with the imaging mode selected using clearly marked indicator on the assembly. Appropriate system sensors will confirm that position is correct and advise the user in the contrary. Same for Head I and Head ll.
- The system will automatically rotate the Outer Cylinder so that the opening of the Cylinder is consistent with the current detector position. Appropriate system sensors will confirm that position is correct and advise the user in the contrary.
For Head I and Head 11.
- When all positions and all orientation conform to the gantry position and image type requested, the green LED will become orange.
- Proper gantry motions will then be performed p V.6 Ik
- Whenever the source leaves the park position and is effectively exposing the object, the orange LED will tum red.
- After the imaging (transmission) session, the source will go back in the park position and the user will be asked the next step (chain to another transmission protocol or going back to normal mode).
- User will be asked through messages on the computer screen to manually reposition the Cylinder in the permanent storage position by rotating the supporting arm on Head I and Head ll. No gantry motion inconsistent with the Source Holder position will be performed unless the system sensors confirm that all sources and source holders are in permanent storage position. At that point, a green LED willindicate that the system is ready for normal use.
Even for a triple detector machine, only Head I and Head ll are going to be equipped with the extemal source.
t What ifs i
System sensors will monitor the source location in the Outer Cylinder, the location of the Cylinder itself and obviously the position and orientation of the detectors. Any inconsistency between all the sensed positions will result in aborting the current imaging session and either park the source in
. the storage position (if possiblo) and/or ask the user to manually reposition the Cylinder in the permanent storage position while the prcblem is being investigated by qualified personnel.
In the event of a power outage where no gantry or computer action is possible, the activity will still be contained in the volume defined by the detectors (that will act as very efficient shielding material. Since no imaging can be performed in this situation, we have to assume that the patient will be removed from the imaging region and the medical personnel will take proper actions. In the
. event that the source is stuck mid travel inside the Cylinder during a power outage (and no message can be sent to the user via computer or LED) a battery-powered beeper (inhibited in conditions of normal use) will signal to the personnel that the source is exposed. This represents the worst situation. More and more cameras are put on autonomous power system and proper instructions will be added and given to the user in the shut off procedure resulting from a power outage.
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\\..... /g WASHINGTON, D.C. 20ee6-0001 Ronald J. Martone Manager of Regulatory Compliance Picker internationalInc.
Nuclear Medicine Division 595 Minor Road Highland Heights, OH 44143
Dear Mr. Martone:
Folowing a cursory review of the BEACON system based on the design specifications included
- in your letter dated June 11,1998, we hope that the following suggestions may be helpful to the development f o~d fMW"'O evaluation " ' '
,4 pM. *~-
n On.o 1.
Please note that although the collimated beam will remain in the confinement of the detectors, the NRC does not considered this an adequate safety' measure'in the event that a source could become stuck in an exposed position. What fail-safe measures are provided in cases of power failures or other problems when source is in exposed.
position? One suggestion would be to include a retractable spring mounted to the inner cylinder, in which in the event of a power failure the inner cylinder would be retracted automatically into a shielded parked position under the tension of the spring. In addition, in the event of any unforseen computer " glitches" or other problems,1 cutting the power would be a sensible emergency procedure.
2.
In addition to the LED indicators or electronic sensors monitoring source status (i.e.,
- parked, exposed) the NRC usually suggests including some sort of mechanical indicator for determining source position. LEDs or electronic sensors may not be one-hundred percent reliable, due to burn-outs or power-failures.; Also, the exact position of the source is not known with these components Therefore, we suggest incorporating into the device a mechanical ruled indicator directly linked to the inner cylinder drive mechanism. This indicator should be easily visible without need for an operator to look into or bend over exposure regions.
The NRC relies substantially on prototype testing to venfy thak the device will remain
- 3.
operational when subjected to conditions associated with normal handling and use, and
- will maintain its containment (e.g., no loss of byproduct material nor significant loss of shielding) with the necessary safety featured remaining operable. Picker will need to
- demonstrate that the device will remain its integrity after being subjected to repeated
- cycling and likely impacts during use. n
- Cycle testing must demonstrate that the device will remain operational after the
' expected number of cycles over the years of use of the device This can be g
m accomplished by subjecting a prototype unit to the expected number of cycles a device.
may encounter during its useful life..
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i
~
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I Picker may demonstrate the device will withstand likely impacts encountered during use.
l The device does not need to remain operational after impact but there must not be a loss or radioactive material nor significant decrease in shielding. This can be accomplished by subjecting a prototype unit to multiple drops onto a hard surface from the height of the device during normal use.
1 Sincerely, j
l
~l Eric B. Compton, Engineering Aide Materials Safety Branch 4
Division of Industrial and I
Medical Nuclear Safety Office of Nuclear Material Safety and Safeguards 1
Distnbution:
IMNS r/f ;
NE02-SSD-7 DOCUMENT NAME: H:\\ERIC\\OTHER\\ PICKER.SUG J T3 eseelve a espy of this clocument, andleste in the bos: *C" = Copy without ettechment/ enclosure. E" = Copy with attachment / enclosure
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