1 Management of Radioactive Waste in a Nuclear Medicine Department
A Medical Physics Perspective
Dr. Jennie Cooke Medical Physics and Bioengineering Dept St. James’s Hospital 2 Technetium-99m – the (almost) ideal isotope for diagnostics 3
• Produced from a Mo-99 generator
• Gamma emitter with energy 140keV
• Half-life of 6 hours
• Can be labelled to a wide range of pharmaceuticals
• Imaging is performed with a SPECT system (Single photon emission computed tomography) typically with CT (x-ray) attenuation correction.
• Short lived waste (typically < 48 hours storage)
• Workhorse isotope – relatively large volumes of waste Se-75 - tauroselcholic [75 selenium] acid 4
• Mimics bile acid for the diagnosis of bile acid malabsorption
• Half-life – 120 days
• Activity administered is very low - < 370kBq
• Outpatient protocol Ga-68 PET imaging – the new wave 5 • Produced from a Ge-68 generator
• Positron emitter - annihilation producing 2 x 511keV photons
• Half-life of 68 minutes
• Can be labelled to a range of ligands
• Imaging is performed with a PET system (Positron emission tomography) typically with CT (x-ray) attenuation correction.
• Short lived waste (typically < 12 hours storage)
• Synthesis of gallium peptides produces a large volume of waste. Some contamination with Ge-68 (half life 271 days) is unavoidable. 6
Radiopharmaceutical Preparation
Patient administration
Uptake time & inpatients A Simple Radiopharmaceutical Preparation 7
Operator dresses in PPE – disposable gown and gloves.
Operator prepares a drip tray in the laminar flow cabinet lined with a low lint wipe to absorb spills.
Technetium - 99m (Tc-99m) is eluted from the generator into a glass vial.
A glass vial of radiopharmaceutical is swabbed with an alcohol wipe. Spills of Tc-99m are also absorbed using these.
The required volume of Tc-99m is drawn from the eluate vial using a syringe and needle.
The Tc-99m is diluted with saline from a 10ml plastic vial of NaCl. A Simple Radiopharmaceutical Preparation 8
Operator dresses in PPE – disposable gown and gloves.
Operator prepares a drip tray in the laminar flow cabinet lined with a low lint wipe to absorb spills.
Technetium - 99m (Tc-99m) is eluted from the generator into a glass vial.
A glass vial of radiopharmaceutical is swabbed with an alcohol wipe. Spills of Tc-99m are also absorbed using these.
The required volume of Tc-99m is drawn from the eluate vial using a syringe and needle.
The Tc-99m is diluted with saline from a 10ml plastic vial of NaCl. More complex operations… 9
In vitro red blood cell labelling with Tc-99m
In vitro white blood cell labelling with In-111
Blood handling for glomerular filtration rate measurements
Complex labelling processes such as synthesis using larger disposables such as cassettes. More complex operations… 10
In vitro red blood cell labelling with Tc-99m
In vitro white blood cell labelling with In-111
Blood handling for glomerular filtration rate measurements
Complex labelling processes such as synthesis using larger disposables such as cassettes. 11 RadiopharmacyRadiopharmacy Waste Waste Segregation Segregation
Tc-99m Tc-99m Long-lived Long lived Non- Sharps: non- isotopes isotopes radioactive sharps: sharps: non-sharps waste Needles Gloves Synthesis cassettes Glass vials Gowns Wipes Synthesis waste vials Tray liner Radiopharmaceutical Administration 12
Intravenous: Capsule: Ventilation Study: Cannula Cup Vapourisation set PPE Gloves Absorbent sheets 13 InjectionRadiopharmacy Room Waste Waste Segregation Segregation
All other waste returned to Tc-99m Sharps: Tc-99m non- sharps: radiopharmacy for Needles Gloves disposal Cannulas Gowns Wipes Absorbent sheets Waste production during uptake time and from inpatients 14 Diagnostic Radiopharmaceutical Challenges 15
1. Segregation failures – larger volumes of long lived waste.
2. Long-lived contaminants: I-123 preparation which should have a half-life of 13.2 hours contains longer lived isotopes in small quantities: I-125 with a half-life of 60 hours and Te-121 (20 days).
Rather than expected max. storage of 160 hrs – we find we are storing large numbers of vials for >6 months. Radioiodine therapy for thyroid cancer 16 The original targeted radiotherapy – iodine is only absorbed by thyroid tissue.
Patients first have total thyroidectomy.
Iodine-131 is both a beta and high energy (364keV) gamma emitter (therapy and diagnostic imaging possible).
I-131 has a half-life of 8 days. Gamma photons can be detected by gamma camera sometimes producing the I-131 is administered in capsule form. characteristic star artifact.
Beta particles are absorbed by and ablate any residual thyroid cancer cells. Radioiodine therapy for thyroid cancer 17
• I-131 ablation patients are inpatients
• There are no side effects and patients must be self-caring.
• Specially designed lead lined isolation suite, which is a controlled area when a treated patient is resident.
• Excretion is predominantly urinary
• All bodily fluids are contaminated during the first few days. Radioiodine therapy – sources of waste 18 Radioiodine therapy – sources of waste 19
In-sink In room washing Sharps macerator machine Radioiodine therapy – waste storage 20
• Large volumes of waste
• Often contaminated with decaying food (risk of pests)
• Stored for up to six months Radioiodine therapy – special waste challenges 21
• Patient with non-emptying colostomy bag
• Storage required for six months
• Concerns re odours and patient privacy
• Solution was to source a metal drum with airtight seal Radioactive waste storage 22
Waste is tagged, labelled with trefoil, isotope type and date.
Transferred to short term waste store which is restricted by swipe access and locked out of hours.
Longer lived isotopes store in long-term waste store where available (fire proof, alarmed).
Remnants of vial containing prepared radiopharmacuticals (I-123, In- 111) and unused capsules (Se-75, I-131) stored in a locked safe inside waste store.
All waste is stored until decayed to background levels (typically 6-12 half-lives). This is measured using a contamination monitor (scintillation where available, this varies from site to site). Final disposal 23
• Waste item measured using contamination monitor.
• If no measurement above background detected item can be disposed.
• Tags and trefoils are removed.
• Item is removed from waste register.
• All waste items tagged with cable tie with identifying number.
• Moved to general waste collection point.