F-18 Injection & Uptake

Patient Injection: Injection either in Hot Lab or Uptake Room with a typical dose: 370 -740 MBq (10-20 mCi)

FDG Uptake: Patient waits for 60-90 minutes

Activity will decay while waiting. Remaining activity 0.83, 0.68 and 0.57 for wait time 30, 60 and 90 minutes, respectively

F-18 Scanning

Patient Void: Patient clears ~15% just before scanning

Patient Scan: Whole-body PET scan for 30-60 minutes

Radiation Safety: Areas of Concern

•        Adjacent offices  
  

•        Adjacent hallways  
  

•          Rooms with radiation sensitive equipment (i.e. cameras, uptake systems)  

Storing Patients

Waiting rooms will probably need additional shielding

•         Dose to employees  
  

•         Dose to visitors  
  

•         High background for imaging

Previously indicated…patients wait 30-90 minutes

Transient Patients

•         Some departments do not have a waiting area near
  injection room  
  

•         Radiation from patient may have effect on radiation 
  sensitive equipment (increased background)  
  

  •         Scintillation well counters  
    

  •         Thyroid uptake systems  
    

  •         Scintillation cameras  

How Much Shielding is Needed For PET?  

ALARA Recommendations

• Many facilities have set ALARA limits to be 10% of the applicable limits for radiation workers  
  

• 5 mSv/yr (500 mrem/yr)  

More Lead The Better??

•         Not exactly true  
  

•         Yes…it will reduce exposure rates  
  

•         Yes…it is $$$$

Each institution must find a happy medium between safety and cost (isn’t that ALARA principle?)

Factors Affecting Radiation Protection

•         Number of patients imaged  
  

•         Activity administered per patient  
  

•         Length of time patient remains in facility  
  

•         Location of department within facility

        Physicist perform calculations based on:

•         Number of patients imaged  
  

•         Activity administered per patient  
  

•         Length of time patient remains in facility  
  

•         Location of facility relative to controlled and uncontrolled areas

Determine amount of shielding needed to keep doses ALARA

Suggestions:

•          Imaging room will most likely need additional shielding  
  

•         Many facilities add ½ inch lead in walls facing occupied areas (offices, busy hallways)  
  

•         Some could add only ¼ inch if they do not expect a large patient load (realistic??)  
  

•         Some facilities only add ¼ inch lead in walls facing semi-occupied areas  
  

•           Don’t forget floors and ceilings  
   

•         If patient load is high enough, shielding may be needed

 

Photograph illustrating sheets of lead installed during construction of imaging room.

Photograph illustrating shielded space for Nuclear Medical Technologists in PET Imaging facility-  Leaded Glass Windows and Lead in Walls.

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Portable Shielding:

•         Pb shields 2.5 and 5.0 cm thick are available  
  

•         Dose reduction factors of 40 and 1900 respectively

Problems

•         Patient may move in relation to gantry  
  

•         Shield can limit access to patient

Portable Shield Warning

•         Traditional portable shields not adequate  
  

•         Only have a few mm of lead  
  

•         Won’t do much to stop 0.511 MeV photons

PET/CT Shielding

PET uses high levels of high energy photons

CT uses higher levels of low energy photons (x-rays)

If shielded for PET – no additional shielding needed

If shielded for CT only – additional shielding will be necessary