"Ionizing Radiation in Medicine "

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  • Why this is important enough to talk about. Widespread use, increasing use, few practitioners suggest this to ba a growth field.
  • While experimenting with the Crookes tube (precursor of the modern x-ray tube) Wilhelm Konrad Roentgen discovered X-rays in 1896 when he noticed phosphorescence emanating from a plate in the beam. Knowing that this was caused by some type of radiation, but not knowing what kind, he called them “x-rays”. Henri Becquerel discovered radioactivity while conducting experiments on Roentgen’s findings. He wrapped a photographic plates in brown paper along with a fluorescent material, potassium uranyl sulfate. When he attempted his experiment he found that the plates were all fully exposed even though they had not been exposed to light. Max Planck developed much of the conceptual framework for what would become the field of Quantum Mechanics. His work was extended by Albert Einstein and led to the famous equation, E=mc 2 Einsteins’ work led to a new understanding of light as having both particulate and wave characteristics. By equating energy with mass, his work was fundamental to the development of nuclear physics as a field. By bombarding elements with neutrons radioactive elements could be synthesized, with varying types of emissions of varying energies, and having unique interactions with matter
  • A patient receives a certain amount of radiation dose from nuclear medicine studies which is comparable to, and often much less than, many diagnostic x-ray studies or the natural background radiation dose one receives just by living on earth. The amount received from the diagnostic tests is not harmful to the patient
  • Discussion of Nuclear instability, radiation emissions, energy/mass conversions, half-life, in order to provide basis for discussion of physical characteristics of emissions. Why does an alpha particle have a high LET, what happens to the nuclide, how do these radiations form. Nucleus: Protons positively charged. Within the nucleus in very close proximity. Tendency is to repel each other. This tendency is countered by neutrons. With increasing atomic number (number of protons), atomic mass (mostly from number of protons + number of neutrons) increases at a greater rate. H – at # 1, mass 1 1 proton, 0 neutrons He at # 2, mass 4 2 protons, 2 neutrons Tc99 # 43, mass 99 43 protons, 56 neutrons I131 # 53, mass 131 53 protons, 80 neutrons U238 # 92, mass 238 92 protons, 146 neutrons
  • Physicists worked extensively on gaining an understanding of radioactivity and were able to differentiate between alpha, beta, gamma, and neutron emissions. Einstein’s special theory of relativitiy led to Planck’s development of quantum theory; work on these theories led to a deeper understanding of radiation as having both wave and mass (particulate) characteristics, of the relationship between mass and energy (E=mc 2) , and of the process of radioactive decay. Fermi’s work at Univ. of Chicago led to the development of a nuclear reactior that could produce radionucliides including trans-uranic elements in abundance.
  • Biological half life: based on excretion and metabolism. Important in pharmacology and toxicity studies. LET – rate of deposition of energy from radiation particle. High LET means rapid deposition, usually over short distance. RBE – relative biological effect is based on radiosensitivity of tissue. RBE correlates with metabolic rate. “ Q” factor – refers to the relative biological impact of different emissions. Values are standardized by the government and published in 10CFR. “Q” factors: photon, electron = 1; neutron = 10; alpha = 20. photon, beta and neutron are all relatively low LET ( linear energy transfer ) radiations, in which the ionizations caused by the radiation are separated by many thousands of ångströms (Å), alpha radiation is a high LET radiation, with the ionizations occurring essentially about every ångström of travel of the alpha particle
  • cell damage based on # of ionizations #ionizations correlates positively with increasing LET range of approximately 5-9 micrometres, or roughly the thickness of one cell diameter ionizations disrupt chemical bonds (DNA) and create free radicals
  • LET comparison between two radiations, an alpha and a beta. Alpha particles expend a large amount of energy in a short distance making them dangerous to growing tissue. They cannot penetrate the outer surface of the skin, however, so they pose little external threat. Beta particles penetrate more deeply but deposit relatively less energy than an alpha. Strength comes in numbers, and sensitivity of tissue.
  • positron (positive charge electron analog) from nucleus interacts with electrons in surrounding (target) cells. Resulting annihilation event yields two 511 keV photons travelling in opposite directions. When captured in a gamma camera this characteristic allows precise localization of event. Key is to deliver radiopharmaceutical to target cell. Glucose is rapidly absorbed by brain tissue making this an ideal brain imaging modality. Limitation: availability of positron emitters. Short half-life makes transport impractical forcing patient to travel to a facility with a cyclotron.
  • Brain SPECT Also known as "Neurolite brain SPECT" or "brain SPECT with and without Diamox." This study determines the blood perfusion of the brain. Diamox is used to increase blood flow to the brain and is used in conjunction with Neurolite in some cases. Indications (incomplete list) Alzheimer's Dementia Atrophy Head trauma Chemical exposure Lyme disease Vascularitis Drug toxicity Diamox Contraindications Patients who suffer from migraine headaches and/or are allergic to sulfa drugs should not have Diamox. Adenosine is used as a substitute. Preparation No stimulants 12 hours prior to exam. This includes caffeine and some medication. Scheduling This is a two-part study that requires two seperate visits The two studies should be at least two days apart but not more than a couple months apart Schedule after 1 p.m. only, due to dose availability Procedure time is approximately 1.5 hours for the baseline study Procedure time is approximately 2.5 hours for the Diamox Additional Resources Patient Information Sheet for Brain SPECT. Brain SPECT Showing Alzheimer's Disease   © Copyright 2000-2008 Cedars-Sinai Health System. All rights reserved. Privacy Policy Terms and Conditions http://www.csmc.edu/9663.html
  • Full history: 27 year-old woman initially diagnosed with invasive ductal carcinoma by ultrasound guided biopsy. She underwent bilateral mastectomy, chemotherapy, and right-sided radiation. Radiopharmaceutical: 15.0 mCi F-18 Fluorodeoxyglucose i.v. Findings: FDG-PET imaging demonstrates innumerable areas of increased uptake consistent with diffuse metastatic disease. The whole-body bone scintigraphy study initially performed for right rib pain demonstates focal mildly increased activity in the superior right parietal skull, right lower sternum, left anterior 6th rib, right aspect of L4, superior right acetabulumamd medial proximal right femur. Discussion: FDG-PET scanning is a valuable tool to image aggresive neoplasms such as breast cancer. Evaluation of extent of disease is crucial to therapy and overall prognosis. Bone scintigraphy likely significantly underestimated the extent of skeletal metastases.
  • Full history: 27 year-old woman initially diagnosed with invasive ductal carcinoma by ultrasound guided biopsy. She underwent bilateral mastectomy, chemotherapy, and right-sided radiation. Radiopharmaceutical: 15.0 mCi F-18 Fluorodeoxyglucose i.v. Findings: FDG-PET imaging demonstrates innumerable areas of increased uptake consistent with diffuse metastatic disease. The whole-body bone scintigraphy study initially performed for right rib pain demonstates focal mildly increased activity in the superior right parietal skull, right lower sternum, left anterior 6th rib, right aspect of L4, superior right acetabulumamd medial proximal right femur. Discussion: FDG-PET scanning is a valuable tool to image aggresive neoplasms such as breast cancer. Evaluation of extent of disease is crucial to therapy and overall prognosis. Bone scintigraphy likely significantly underestimated the extent of skeletal metastases.
  • 49 year old man presents for staging after grossly complete excision of a high grade fibrosarcoma from the right groin 1.5 weeks earlier. Although the surgery was uneventful, the patient had progressively increasing pain at the surgical site following removal of a drain 4 days earlier. He also reported a remote history of rectal cancer, status post abdominoperineal resection 13 years ago, from which he was presumably cured
  • F-18 FDG PET reveals a rim of intensely increased activity surrounding a photopenic region in the anterior abdominal wall at the site of prior surgery. Several small foci of increased uptake adjacent to this region were also noted, as well as increased uptake within two right internal iliac and one left inguinal lymph node
  • Imaging of brain trauma TBI Clinical Policy Bulletin: Single Photon Emission Computed Tomography (SPECT) Number: 0376 Policy Noncardiac Indications : Aetna considers single photon emission computed tomography (SPECT) medically necessary for any of the following indications: Diagnosing and assessing hemangiomas of the liver; or Presurgical ictal detection of seizure focus in members with epilepsy (in place of positron emission tomography (PET)); or Assessment of osteomyelitis, to distinguish bone from soft tissue infection; or Localization of abscess, for suspected or known localized infection or inflammatory process; or Differentiation of necrotic tissue from tumor of the brain; or Lymphoma, to distinguish tumor from necrosis; or Neuroendocrine tumors, diagnosis and staging; or Detection of spondylolysis and stress fractures; or Imaging of parathyroids in parathyroid disease. Aetna considers SPECT experimental and investigational for all other noncardiac indications, including any of the following, because its diagnostic value has not been established in the peer reviewed medical literature in these situations: Initial or differential diagnosis of members with suspected dementia (e.g., Alzheimer's disease, vascular dementia, dementia with Lewy bodies, and frontotemporal dementia); or Diagnosis or assessment of stroke members; or Scanning of internal carotid artery during temporary balloon occlusion; or Diagnosis or assessment of members with attention deficit/hyperactivity disorder ( CPB 426 - Attention Deficit/Hyperactivity Disorder ); or Diagnosis or assessment of members with autism ( CPB 648 - Pervasive Developmental Disorders ); or Diagnosis or assessment of members with personality disorders (e.g., borderline personality disorder, anti-social personality disorder including psychopathy, schizotypal personality disorder, as well as aggressive and violent behaviors); or Diagnosis or assessment of members with schizophrenia; or Differential diagnosis of Parkinson's disease from other Parkinsonian syndromes; or Prosthetic graft infection; or Vasculitis. Cardiac Indications : Aetna considers SPECT medically necessary for the following indications for members who do not meet any of the exclusion criteria below: Diagnosis of coronary artery disease (CAD) in members with an uninterpretable resting electrocardiogram (ECG) and restricted exercise tolerance; or Assessing myocardial viability before referral for myocardial revascularization procedures. source: AETNA insurance policy letter
  • Movie shows the typical pattern of atrophy found in Alzheimer patients. It can be distinguished from the ischemic disease scan by following up with a scan performed following a Diamox injection. If the perfusion improves, it is more than likely an Alzheimer type disorder. If the infarcted areas become worsened, it would suggest an ischemic disorder
  • “ Hot spots” indicating high rate of uptake of radiopharmaceutical (Tc99-m) Right tibial shaft suggests hypermetabolic state
  • 18 yo. male with darkening urine, worsening muscle pain, and decreasing urine output over the past 3 days after one day of intense physical exercise Diagnosis: Rhabdomyolysis Full history: 18 yo. male who presented from an OSH with rhabdomyolysis and acute renal failure. He reported a 3-day history of darkening urine, increasing muscle pain, and decreasing urine output after one day of intense physical training. Patient reported taking 2 tablets of KCl after finishing training and multiple tablets of ibuprofen to control muscle pain with no relief. Whole body bone scintigraphy was ordered to identify the extent of involvement of rhabdomyolysis as there was concern about the development of compartment syndrome in the affected muscles. Findings: There is intense uptake in the thighs bilaterally, particularly in the vastus lateralis and medialis muscles. In the vastus medialis muscles bilaterally, there is a central area of decreased activity which suggests more extensive necrosis in these areas. There is also moderate uptake in the triceps bilaterally and mild uptake in the rectus muscle superiorly. Additionally, uptake in the kidneys is higher than normal, and no bladder activity is seen, consistent with the patient's acute renal failure. Discussion: Tc-99m MDP can accumulate in soft tissue as a result of a number of different conditions and is probably the result of soft tissue calcification or infarction. In rhabdomyolysis, the mechanism of uptake is thought to be related to muscle cell injury and subsequent infarction, which disrupts the local calcium-phosphate balance, causing Tc-99m to be deposited in the areas of involvement. However, inflammation of the affected muscles could also increase flow and uptake of the tracer. Bone scintigraphy can be used to identify all involved muscle groups and the degree of involvement, as it was in this case. Causes of rhabdomyolysis, besides intense physical exercise, include crush injury due to trauma and adverse reactions to drugs, such as statins, or drugs of abuse, such as cocaine.
  • Combination of PET with CT and MRI PET scans are increasingly read alongside CT or magnetic resonance imaging (MRI) scans, the combination ( "co-registration" ) giving both anatomic and metabolic information (i.e., what the structure is, and what it is doing biochemically).
  • Tubes surgically implanted based on tumor geometry establish radiation field around tumor Radioactive “seeds” emplaced dose calculated by medical physicist activity and geometry critical
  • Tubes surgically implanted based on tumor geometry establish radiation field around tumor Radioactive “seeds” emplaced dose calculated by medical physicist activity and geometry critical
  • The American Cancer Society (2001) estimated 182 800 new cases of invasive breast cancer in the year 2000 among women in America, and 40 800 are expected to die from the disease (American Cancer Society, 2000). Novel, more effective treatments that overcome this problem in breast cancer management are essential. Targeted therapy, first discussed over 100 years ago, is based on the idea that a drug will attack its target without damaging other tissue ( Raso, 1990 ). Targeted alpha therapy (TAT) uses an -emitting radionuclide as a lethal medicament via an effective targeting carrier to kill cancer cells ( McDevitt et al , 1998 ; Allen, 1999b ). We are investigating a novel targeting approach that exploits the involvement of cell-surface receptor bound urokinase plasminogen activator (uPA) in the metastatic spread of breast cancer cells ( Kruithof et al , 1995 ). -emitting radionuclides emit particles with energies of 4–8 MeV, which are up to an order of magnitude greater than most rays. Yet, their ranges are two orders of magnitude less as particles have a linear energy transfer (LET) which is about 100 times greater ( Allen, 1999a ). This is manifested by a higher relative biological effectiveness (RBE). As a result, a much greater fraction of the total energy is deposited in cells with 's and very few nuclear hits are required to kill a cell. Consequently, only radiation has the potential to kill the metastatic cancer cells at tolerable dose limits, whereas the low LET of 's makes this a very difficult task within human dose tolerance limits.
  • Patients are first given an intravenous injection of a boron-10 tagged chemical that preferentially binds to tumor cells. In clinical trials performed so far the neutrons are created in a nuclear reactor , but particle accelerators may also be used to collide protons into targets made of lithium or beryllium. The neutrons pass through a moderator, which shapes the neutron energy spectrum suitable for BNCT treatment. Before entering the patient the neutron beam is shaped by a beam collimator. While passing through the tissue of the patient, the neutrons are slowed by collisions and become low energy thermal neutrons. The thermal neutrons undergo reaction with the boron-10 nuclei, forming a compound nucleus (excited boron-11) which then promptly disintegrates to lithium-7 and an alpha particle. Both the alpha particle and the lithium ion produce closely spaced ionizations in the immediate vicinity of the reaction, with a range of approximately 5-9 micrometres, or roughly the thickness of one cell diameter. This technique is advantageous since the radiation damage occurs over a short range and thus normal tissues can be spared.BNCT has been experimentally tested primarily as an alternative treatment for malignant brain tumors called glioblastoma multiforme as well as recurrent, locally advanced head and neck cancer . Although there are reports of some successful outcomes, this approach has not yet been shown to be superior to other current therapies. Hence, BNCT has not entered routine clinical use
  • imaging technology to identify abnormal areas in the brain with pinpoint accuracy, so an array of radiation beams can be focused precisely on the target from many different directions. Each individual radiation beam is too weak to harm the brain tissue it passes through. The damage occurs only at the spot in the brain where all the beams meet. With the help of a computer, this spot can be accurately plotted to within a fraction of a millimeter. Brain tumors. Radiosurgery is useful in the management of both benign and malignant brain tumors, especially tumors originating elsewhere in the body that have metastasized to the brain. Radiosurgery often can treat tumors that may have been termed inoperable because of their location in hard-to-access areas of the brain. Arteriovenous malformations (AVMs). AVMs are abnormal collections of arteries and veins that connect directly, instead of through a network of capillaries. When located in the brain, these abnormalities can cause severe bleeding, headaches or seizures. While many AVMs can be removed with conventional microsurgery, radiosurgery may offer a much less invasive option with less risk of neurologic injury. Trigeminal neuralgia. This nerve disorder causes disabling facial pain that feels like an electric shock. Radiosurgery can create a lesion on the nerve, blocking its pain signals. This procedure is typically reserved for older patients or for patients with recurrent pain after other operations for trigeminal neuralgia. Acoustic neuromas. These noncancerous tumors, also called schwannomas, develop on the nerve that affects balance and hearing. Radiosurgery can effectively control the growth of small tumors in the majority of cases, with a lower risk of deafness or loss of facial movement, compared with conventional surgery. Pituitary tumors. Tumors of the pea-sized "master gland," which is located deep within the brain, can cause a variety of problems because the pituitary controls the thyroid, adrenal and reproductive glands. Radiosurgery may be employed to stop the growth of the tumor and halt the abnormal hormone secretion that can occur from these tumors
  • imaging technology to identify abnormal areas in the brain with pinpoint accuracy, so an array of radiation beams can be focused precisely on the target from many different directions. Each individual radiation beam is too weak to harm the brain tissue it passes through. The damage occurs only at the spot in the brain where all the beams meet. With the help of a computer, this spot can be accurately plotted to within a fraction of a millimeter. tumor and halt the abnormal hormone secretion that can occur from these tumors Gamma knife The gamma-knife machine was the first instrument developed for radiosurgery. The instrument precisely focuses 201 beams of gamma radiation on a precisely located area, each beam originating from a slightly different point. Before the procedure, a box-shaped frame is attached to your head with four pins. This frame stays in place throughout the treatment. In addition to holding your head perfectly still, the head frame serves as a reference point in determining exactly where the beams of radiation should converge. The head frame is actually the key to the precision of the gamma-knife machine. Once the frame is attached to your head, imaging scans — such as magnetic resonance imaging (MRI), computerized tomography (CT) or conventional X-rays of brain circulation taken after injection of a substance that makes the blood vessels show up (cerebral angiography) — are performed. The results are fed into the gamma knife's computerized planning system. This planning process may take several hours. During that time, you can relax in another room, but the head frame must remain attached to your head. When it's time for the treatment, you recline on a pallet that slides into the gamma-knife machine. Your head frame is attached securely to a helmet inside the machine. Treatment times vary, depending on the size and number of targets. This procedure works best for targets less than 4 centimeters in size.
  • Gamma knife equipment. Clockwise from top left: Frame, shield, emplaced on patient, machine view
  • "Ionizing Radiation in Medicine "

    1. 1. HOT STUFF Ionizing Radiation in Medicine
    2. 2. Objectives • History of nuclear medicine • Benefits of Nuclear Medicine • Radiation Biology: interactions and effects • Diagnostic and Therapeutic Applications • Common Nuclear Medicine procedures
    3. 3. Overview • Over 20 million procedures annually in US • Provides information unobtainable by other means • Useful for diagnosis and therapy • Sensitive, can detect many diseases at early stages • Less expensive than exploratory surgery • Based on ionizing radiation • Allows evaluation of physiologic function • Non-invasive, painless
    4. 4. Historical Perspectives • 1896 X radiation discovered by Roentgen • 1896 Ionizing radiation discovered by Becquerel • 1900 Quantum Hypothesis - Planck • 1905 Special Theory of Relativity - Einstein • Continuing interest led to development of the field of Radiation Physics • Advances allowed for the creation of isotopes – varying physical characteristics • 1951 FDA approves I131 as radiopharmaceutical
    5. 5. How it Works Physical and Biological Considerations
    6. 6. Basic Concept • Radiation is used to image or treat disease – external or internal source • Radiopharmaceutical is selected – physical characteristics of radiation source – biological characteristics of target cells • Radiation dose is administered to patient – inhalation, ingestion, injection, or external beam • Imaging is possible due to radiation energy • Therapy is possible due to radiotoxicity
    7. 7. Radiation Physical Characteristics • Nucleus – protons, neutrons – neutrons “stabilize” nucleus • Nuclear instability – increasing nuclear mass => decreasing nuclear stability • Decay to stable state through loss of mass – as energy (E=mc2) in the form of photons – as particles: alpha, beta, positron, neutron • Radiological half-life – time to decay to one-half original activity
    8. 8. Radiation Decay Products • Alpha particle – high mass (2 neutron, 2 protons) – low velocity • Beta – low mass (electron) – intermediate energy • Gamma – very low mass (photon, wave-particle duality) – energetic • Neutron – wide range of energies – activation
    9. 9. Biological Effects Tissue Interaction • Ionizing Radiation Toxicity – disrupts cellular DNA – creates free radicals (peroxides) • Linear Energy Transfer (LET) • Tissue radiosensitivity – relative biological effect – uptake and elimination
    10. 10. Toxicity Cellular Effects • Function of ionization density • DNA bonds – repair mechanism overwhelmed – increased mutations – loss of ability to replicate • Free radicals – destruction of cellular contents
    11. 11. Biological Interactions Linear Energy Transfer (LET) • Measure of ionization density – ionizations/unit volume • Energy (eV) deposited per micrometer of travel – Low LET: gamma, beta, x-radiation – High LET: alpha, neutron radiation
    12. 12. Linear Energy Transfer FIGURE 4.3 Penetrating power of alpha and beta particles. SOURCE: Courtesy of Joseph Jurcic, Memorial Sloan-Kettering Cancer Center.
    13. 13. Biological Interactions Relative Biological Effect • Relative Biological Effect – relative effectiveness of different emissions in producing a biological effect • Quality factor (Q) – tissue effects of different types of radiation • photon, beta = 1 • neutron = 10 • alpha = 20
    14. 14. Biological Interactions Tissue Radiosensitivity • Metabolic Rate – correlates with nutrient uptake rate • Tissue-specific nutrients, configuration • Replication rate – correlates with nutrient uptake rate • Elimination rate – biological half-life
    15. 15. Biological Interactions Uptake and elimination • Nutrient/substrate uptake – attach nucliide to ligand – preferential uptake by target cells • Glucose in brain • Elimination – biological half-life – matabolism – physical half-life
    16. 16. Radiopharmacy Selection of Agent: Considerations • High LET – high energy deposition in target cells – ionizations produced in target cells • Low LET – little energy absorbed per unit weight – few ionizations produced in tissue • Target cell specificity – uptake • Exposure to surrounding tissue – ALARA
    17. 17. Commonly used Isotopes Isotope half-life Emission Energy keV Yield% Use Tc99m 6.02h Gamma 140 89 multiple I131 8.04d Gamma beta 364 606 81 89 thyroid Xe133 5.24d Gamma beta 81 346 36 99 lung scans In111 2.83d Gamma Gamma 245 171 94 90 leukocytes
    18. 18. Applications in Medicine Diagnostics
    19. 19. Diagnostic Modalities • Positron Emission Tomography (PET) • Single Photon Emission Computed Tomography (SPECT) • Radioimmunoassay (RIA) • Scintigraphy • Co-Registration – PET with MRI or CT
    20. 20. Diagnostic Studies • Renal function • Coronary artery perfusion and cardiac function • Lung scans for respiratory and blood flow problems • Inflammation and infection • Ortho - fractures, infection, arthritis and tumors • Cancer detection and localization – lymph node evaluation, metastases • GI bleed • Thyroid function • Cerebral perfusion and abnormalities (seizures, memory loss, TBI)
    21. 21. Diagnostic Studies Exposure Risk • Low energy gamma and positron radiations • Low exposure (dose) – comparable to diagnostic x-ray studies – natural background radiation • Low risk – dose received is not harmful to the patient
    22. 22. Positron Emission Tomography • F18 FDG (fluorodeoxyglucose) typically used – weak positron emitter (low radiation dose) • Glucose analog – high uptake by brain, kidney, tumor, cardiac, and lung tissue – physiologic function • Excellent 3-D imaging – precise localization of tissue – monitoring therapeutic efficacy
    23. 23. PET Brain
    24. 24. Monitoring Therapy Esophageal tumor • PET more sensitive than CT for monitoring therapy • Expanding role for PET • Society of Nuclear Medicine, Wieder et.al. 2005
    25. 25. Metastatic Breast Carcinoma • 27 year-old woman initially diagnosed with invasive ductal carcinoma by ultrasound guided biopsy. She underwent bilateral mastectomy, chemotherapy, and right-sided radiation
    26. 26. Scintigraphy compared with PET • 27 year-old woman with history of breast cancer
    27. 27. Case Study • 49 year old man presents for staging after grossly complete excision of a high grade fibrosarcoma from the right groin 1.5 weeks earlier • Uneventful surgery • Progressively increasing pain at the surgical site following removal of a drain 4 days earlier
    28. 28. Post-surgical Abscess • 18F PET study
    29. 29. PET Scan Availability • Increasing availabilty – over 1600 centers nationwide – http://petnetsolutions.com/zportal/portals/pat/find_a _pet_center/imagingcenter • Cost – $3 000 to $6 000 – 3 hours for study • Advantages – metabolic scanning • Provider information – http://www.petscaninfo.com/zportal/portals/phys
    30. 30. SPECT • Less expensive than PET – $1000 v $3000 • Widely available • Commonly used for brain scans, perfusion studies • Sensitivity – cerebral ischemia 90% (v 20% CT) @ 8 hours – fracture 80% @ 24 hours, 95% @ 72 hours – seizure (ictal state) 81-93% – myocardial ischemia 90%
    31. 31. Cerebral Ischemia Sensitivity = 90% Clin Nucl Med. 2006 Jul;31(7):376-8
    32. 32. SPECT MUGA Cardiac Function and EF • Tc99m labeled rbc’s • Left ventricular hypertrophy with global hypokinesis • 47 years old with history of CAD
    33. 33. SPECT MUGA Cardiac Function and EF • Tc99m labeled rbc’s • Left ventricular hypertrophy with global hypokinesis • 47 years old with history of CAD
    34. 34. Emission from lateral thighs, right triceps, and inguinal lymph nodes T-cell lymphoma
    35. 35. Scintigraphy • Molecular imaging – indicator of metabolic activity – “hot spots” where uptake is high • Low radiation exposure – Short half-life, low energy gamma radiation • Extensive application in many specialties – Orthopedics, Cardiology, Endocrinology, etc
    36. 36. Case Study X-ray of an 18-month-old boy unable to bear weight on his R leg s/p twisting injury x 2d
    37. 37. Bone Scan at 7 days post-injury
    38. 38. Case Study 18 yo. male with darkening urine, worsening muscle pain, and decreasing urine output over the past 3 days after one day of intense physical exercise
    39. 39. • Elevated kidney uptake w/o bladder activity • Decreased activity in vastus medialis suggests necrosis Rhabdomyolisis
    40. 40. PET/CT Co-registration • Provides anatomical and physiological information
    41. 41. Applications in Medicine Therapeutics
    42. 42. Therapeutic Modalities • Brachytherapy • Ablation • Targeted Alpha Therapy • Gamma knife • External Beam • Boron Neutron Capture Therapy
    43. 43. Therapeutic Applications Examples • Cancer Treatment • Tumor destruction • Palliation of pain • Marrow Transplants
    44. 44. Brachytherapy • Radioactive “seeds” emplaced in surgically implanted tubes • Dose calculation by medical physicist • Tumour geometry determined through imaging modalities
    45. 45. Prostate Cancer Treatment • Tube placement geometry allows creation of interlocking radiation field around target • Field maximizes dose to target while minimizing collateral damage
    46. 46. Iodine Ablation • Ingestion of radioactive cocktail I131 • Dose delivered after surgical thyroidectomy • Patient becomes radioactive • Hospitalized until safe for general public
    47. 47. Targeted Alpha Therapy • Carrier molecule “tagged” with alpha emitter – monoclonal antibodies • Delivery of alpha-emitting isotopes to target – High LET – capable of killing in a range of 1 to 3 cells • Leukemia cells and small solid tumors • Myeloid leukemias, prostate cancer, and lymphoma treatments are under study
    48. 48. Monoclonal Antibody Radioactive Source Chelated to Agent
    49. 49. BNCT • Boron Neutron Capture Therapy • Boron delivered to target cells • Neutron irradiation => activiation of boron • 11Boron decay yields alpha particles – High LET of alpha deposits energy within 3 cell diameters – kills target while minimizing effect to surrounding tissue
    50. 50. Gamma Knife • Precise location and tumor geometry essential • Cobalt-60 source – high level of penetrating gamma rays • Two hundred one beams focused on target • Delivery controlled by shield • Frame emplaced to hold shield • Procedure lasts about 4 hours
    51. 51. Therapeutic Benefits • Brain tumors – (benign and malignant) brain tumors – metastatic lesions – allows treatment in hard-to-access (inoperable) areas of the brain. • Arteriovenous malformations (AVMs) – in brain can cause severe bleeding, headaches or seizures • Trigeminal neuralgia – create a lesion on the nerve blocking its pain signals • Acoustic neuromas – lower risk of deafness or loss of facial movement than with conventional surgery. • Pituitary tumors
    52. 52. Gamma Knife • Concept: to create an interlocking field of gamma radiation emissions centered on the target • Tumour geometry is determined via imaging modality
    53. 53. Questions?

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