Radiopharmaceuticals

RADIOPHARMACEUTICALS

Portray the physiology, biochemistry or pathology of a body system without causing any perturbation of function

“radiotracers

Most radiopharmaceuticals are a combination of a RADIOACTIVE molecule that permits external detection and a

BIOLOGICALLY ACTIVE molecule or drug that acts as a carrier and determines localization and biodistribution.

Radionuclides

Refers only to radioactive atoms

Radiochemical

When a radionuclide is combined with a chemical molecule to confer desired location properties

Radiopharmaceutical

Is reserved for radioactive materials that have met legal requirements for administration to the patients or

subjects.

Design Characteristics of Pharmaceuticals

The radionuclide decay should result in gamma emissions of suitable energy and sufficient abundance of

emission of external detection

It should not contain particulate radiation which increases patient’s radiation dose without adding diagnostic

information

Beta emissions are suitable for therapeutic radiopharmaceuticals

The effective half-life should only be longer enough for the intended application, usually a few hours

The specific activity should be high

The pharmaceutical component should be free of any toxicity or secondary effects

Should be readily or easily compounded and should have a reasonable cost.

The agent should rapidly and specifically localize according to the intended application.

Background clearance should be rapid, leading to good target to background ratios

Production of Radionuclides

Artificially produced

Bombardment of medium atomic-weight nuclides with low-energy neutrons in nuclear reactor results in

neutron-rich radionuclides that undergo beta-minus decay

Proton bombardment of a wide variety of target nuclides in cyclotrons or other special accelerators produces

proton-rich radionuclides that undergo positron decay or K-capture

Radionuclides Generators

One of the practical issues faces in NM is the desirability of using relatively short-lived agents and at the same

time the need to have radiopharmaceuticals delivered to hospitals or clinics from commercial sources

The solution to this dilemma is the use of Radionuclide Generator Systems

With this combination of half-lives, the generator can be shipped from a commercial vendor and the daughter

product will still have a useful half-life for clinical application.

Radionuclides Parent: MO-99 Daughter: Tc- 99m

Half-life 66 hours 6 hours

Mode of Decay Beta Minus Isometric Transition

Daughter Produce Tc- 99m, Tc-99 Tc-99

Principal Photon Energies 740 keV, 780 keV 140 keV

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 Portray the physiology, biochemistry or pathology of a body system without causing any perturbation of function  “radiotracers  Most radiopharmaceuticals are a combination of a RADIOACTIVE molecule that permits external detection and a BIOLOGICALLY ACTIVE molecule or drug that acts as a carrier and determines localization and biodistribution. Radionuclides  Refers only to radioactive atoms Radiochemical  When a radionuclide is combined with a chemical molecule to confer desired location properties Radiopharmaceutical  Is reserved for radioactive materials that have met legal requirements for administration to the patients or subjects. Design Characteristics of Pharmaceuticals  The radionuclide decay should result in gamma emissions of suitable energy and sufficient abundance of emission of external detection  It should not contain particulate radiation which increases patient’s radiation dose without adding diagnostic information  Beta emissions are suitable for therapeutic radiopharmaceuticals  The effective half-life should only be longer enough for the intended application, usually a few hours  The specific activity should be high  The pharmaceutical component should be free of any toxicity or secondary effects  Should be readily or easily compounded and should have a reasonable cost.  The agent should rapidly and specifically localize according to the intended application.  Background clearance should be rapid, leading to good target to background ratios Production of Radionuclides  Artificially produced  Bombardment of medium atomic-weight nuclides with low-energy neutrons in nuclear reactor results in neutron-rich radionuclides that undergo beta-minus decay  Proton bombardment of a wide variety of target nuclides in cyclotrons or other special accelerators produces proton-rich radionuclides that undergo positron decay or K-capture Radionuclides Generators  One of the practical issues faces in NM is the desirability of using relatively short-lived agents and at the same time the need to have radiopharmaceuticals delivered to hospitals or clinics from commercial sources  The solution to this dilemma is the use of Radionuclide Generator Systems  With this combination of half-lives, the generator can be shipped from a commercial vendor and the daughter product will still have a useful half-life for clinical application. Radionuclides Parent : MO-99 Daughter : Tc- 99m Half-life 66 hours 6 hours Mode of Decay Beta Minus Isometric Transition Daughter Produce Tc- 99m, Tc-99 Tc- Principal Photon Energies 740 keV, 780 keV 140 keV

Tc-99m  Readily available  Favorable energy of its principal gamma photon  Favorable dosimetry with lack of primary particulate radiations  Ideal half-life for many clinical imaging studies. Other Single-Photon Agents: Radioiodines I-131 and I- 123 Radioiodine- 131  AS sodium iodine was the first radiopharmaceutical of importance in clinical NM  It was used for routine studies of the thyroid gland for several years in the late 1940s  The disadvantages of I-131 include relatively high principal photon energy, long half-life and the presence of beta particle emission  Remains an important radiopharmaceutical for the treatment of hyperthyroidism and differentiate thyroid cancer.  In nonthyroid imaging applications of I-131, it is common practice to block the thyroid gland with oral iodine to prevent thyroid accumulation I-  I-123 is substituted for I-131 for diagnostic purposes. It has a shorter half-life and its principal photon energy of 159 keV is better suited to imaging with the gamma scintillation camera.  I-123 is now decayed by K-capture and the dosimetry is favorable compared with that of I-  I-123 is now increasingly replacing I-121 for whole body thyroid cancer scans and meta-iodebenzyl-guanidine (MIBG) imaging for neuroblastoma and pheochromocytoma. Indium-  Its principal photon energies of 172 keV and 245 keV are favorable compared with I-  The 2,8 days half-life of In-111 permits multiple-day sequential imaging  Several In-111 radiopharmaceuticals have proven clinically useful. The somatostatin receptor binding peptide, pentetreotid labeled to In-111 binds to a variety of neuroendocrine tumors.  In-111 capromab pendetide is a monoclonal antibody used for recurrent prostate cancer Gallium- 67 citrate  Is transported and extracted like iron, localizing in tumors and inflammatory conditions  However, in many aspects it does not have favorable properties for scintigraphy. It has multiple photopeaks and the most abundant photon has the lowest energy.  Other disadvantage includes slow clearance from background tissues, necessitating delayed imaging at 48 hours.  Early excretion through the kidney and delayed excretion via the bowel make imaging in the abdomen problematic.  Care must be taken to interpret the scintigraphic images with a full knowledge of how long after tracer administration of the study was obtained  Laxatives may be required to clear confusing or obscuring activity from the colon. Thallium- 201  Became clinically available in the mid-1970s as a radiopharmaceutical for myocardial scintigraphy  Behaves as a potassium analog, with high net clearance in its passage through myocardial capillary bed which makes it an excellent marker of regional blood flow to viable myocardium.  major disadvantage of Thallium as a radioactive imaging agent is absence of an ideal photo peak for imaging.

 The dispensing of radiopharmaceuticals is under a series of exacting rules and regulations promulgated by the FDA and NRC as well as state pharmacy boards and hospital radiation safety committees.  These are prescription drugs that cannot be legally administered without being ordered by an authorized individual. The nuclear medicine physician and radiopharmacy are responsible for confirming the appropriateness request, ensuring that the correct radiopharmaceuticals in the requested or designated amount is administered to the px and keeping records of both the request and the documentation of the dosage administration.  Before any material is dispensed, all appropriate quality assurance measures should be carried out.  AS good standard of practice, quality control should always be performed, even when not legally required. Every dose should be physically inspected before administration for any particulate or foreign material, such as bits of rubber from the top of multidose injection vials.  Each dose administered to a patient must be assayed in a dose calibrator. Radiation Safety Procedures  Wear laboratory coats in the are where radioactive materials are present  Wear disposable gloves when handling radioactive materials  Monitor hands and body for radioactive contamination before leaving the area  Use syringe and vial shields as necessary  Do not eat, drink, smoke, apply cosmetics or store food in any area where radioactive material is stored or used  Wear personnel monitoring devices in areas with radioactive materials  Never pipette by mouth  Dispose of radioactive waste in designated, labeled and properly shielded receptacles located in a secured area.  Label containers, vials, syringes containing radioactive materials. When not in use, place in shielded containers or behind lead shielding in a secure area  Before administering doses to patients, determine and record activity  Know what steps to take and who to contact in the event of radiation accident, improper operation of radiation safety equipment, or theft/loss of licensed material. SPECIAL CONSIDERATIONS Pregnancy and Lactation  The possibility of pregnancy should be considered for every woman of childbearing age referred to the nuclear medicine service for a diagnostic or therapeutic procedure  Pregnancy alone is not an absolute contraindication to perform a nuclear medicine study. For example, pulmonary embolism is encountered in pregnant women and is associated with potentially serious morbidity and mortality. Thus, the risk-to-benefit ratio of ventilation-perfusion scintigraphy is high and considered a safe procedure in this circumstance.  The radiation dosage is kept at a minimum. Neither of the radiopharmaceuticals employed (Xe-133 or Tc-99m macroaggregated albumin) crosses the placenta in considerable amounts. On the other hand, radioiodine does cross the placenta. The fetal thyroid develops the capacity to concentrate radioiodine at approximately 10- weeks age of gestation and cases of cretinism caused by in utero exposure to radioiodine. I-131 have been documented.  The management of women who are lactating and breastfeeding an infant is another special problem. The need to suspend breastfeeding is determined by the half-life of the radionuclide involved and the degree to which it is secreted in breast milk.  Radioiodine is secreted by the breast and breastfeeding should be terminated altogether after the administration of I-  For I-123, it has generally been recommended that breastfeeding could safely be resumed after 2-3 days. For Tc- 99m agents, 12-24 hours is sufficient.

Recommendations for Radiopharmaceuticals Excreted Breast Milk Radiopharmaceuticals Advised Ga-67 Citrate Cessation I-131 Sodium Iodide Cessation I-123 Sodium Iodide 2-3 days I-123 MIBG 48 hours TI-201 96 hours In-III Leukocytes 48 hours Tc-99m MAA 12 hours Tc-99m red blood cells in vivo 12 hours Tc-99m pertechnetate 4 hours Dosage Selection for Pediatric Patients  A number of approaches have been proposed for scaling down the amount of radioactivity administered to children. There is no perfect way to do this because of the differential rate of maturation of body organs and the changing ratio of different body compartments to body weight. An approximation based of body weight uses the formula: Pediatric Dose = Patient weight (kg) X Adult Dose 70 kg Another alternative is the use of Webster’s rule: Pediatric Dose = Age + 1 X Adult Dose Age + 7  This formula is not useful for infants. In some cases, a calculated dose may not be adequate to obtain a diagnostically useful study and physician judgement must be used. Medical Event (Misadministration)  The definition and procedures for handling misadministration of radiopharmaceuticals are set out in the Code of federal Regulation (10 CFR-35). However, the terminology has changed. What was previously called a misadministration is now called a Medical Event. The code was revised in 2002. What was previously called a misadministration is now called a Medical Event. The code was revised in 2002.  A medical event is defined by the Nuclear Regulatory Commission (NRC) rules and regulations as a radiopharmaceutical dose administration involving the wrong patient, wrong radiopharmaceutical, wrong route of administration or an administered dose differing from the prescribed dose (exceeds effective dosage equivalent 5 rem to whole body or 50 rem to any individual organ)  After the occurrence of a medical event is recognized, regulations for reporting of the event and management of the patient should be followed. The details are determined in part by the kind of material involved and the amount of the adverse exposure of the patient.  All medical events must be reported to the regulatory agency, the referring physician and the affected patient. Complete records on each event must be retained and available for NRC review for 10 years.  Certain states, called Agreement States, have entered into regulatory agreements with the NRC that give them the authority to license and inspect by-product, source, or special nuclear material used for possessed within their borders.

Wear gloves, disposable lab coats, and booties to clean up spill with absorbent paper.
Put all contaminated absorbent paper in labeled radioactive waste container.
Check the area or contaminated individual with appropriate radiation survey meter.

Radiopharmaceuticals, Assignments of Nuclear medicine

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RADIOPHARMACEUTICALS