1 / 45

RADIOPHARMACEUTICALS: DOSIMETRY UPDATE

RADIOPHARMACEUTICALS: DOSIMETRY UPDATE. Carol S. Marcus, Ph.D., M.D. Prof. of Radiation Oncology and of Radiological Sciences, UCLA. THE MOST IMPORTANT NEWS IS RADAR. RA diation D ose A ssessment R esource.

halle
Download Presentation

RADIOPHARMACEUTICALS: DOSIMETRY UPDATE

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. RADIOPHARMACEUTICALS:DOSIMETRY UPDATE Carol S. Marcus, Ph.D., M.D. Prof. of Radiation Oncology and of Radiological Sciences, UCLA

  2. THE MOST IMPORTANT NEWSISRADAR

  3. RAdiationDoseAssessmentResource

  4. RADARis a web site. It is supported by the SNM Education and Research Foundation. It is the brainchild of Michael G. Stabin, Ph.D., of Vanderbilt University, and Mike is the Webmaster. There is a Board which creates and reviews the RADAR content.

  5. THE URL IS:http://www.doseinfo-radar.com

  6. This web resource contains information on dosimetry of radiopharmaceutical, x-ray, and CT procedures. It calculates dose from multiple patient procedures. It includes children, fetuses, and nursing infants. It also calculates dose to people near patients.

  7. The purpose of this lecture is to acquaint you with the power of this web resource.

  8. This is what our old MIRD phantoms looked like: This is what our old MIRD phantom looked like:

  9. This is what our modern phantom looks like:

  10. And this is our modern fetal model:

  11. RADAR Resources: RADAR ON-LINE DATA:On-Line Decay DataOn-Line Kinetic DataOn-Line Model Dose FactorsINTERNAL SOURCES:Occupational Dose FactorsNuclear Medicine: DiagnosisTherapy

  12. RADAR Resources, cont.: EXTERNAL SOURCES:Monte Carlo ApplicationsExternal Point SourceBeta Dose to SkinImmersion in AirGround ContaminationMedical SourcesVARSKIN codeRADAR SOFTWAREDOSE-RELATED LITERATURE

  13. RADAR Resources, cont.: MEDICAL PROCEDURE DOSE CALCULATOR AND RISK LANGUAGE GENERATOR

  14. RADAR Resources, cont.: Check out the RADAR nuclearmedicine patient exposure radiation dose calculator. It performs dose calculations for release of radioactive nuclear medicine patients and dose from other related situations.

  15. Section I. Patient Release Calculations As noted in our Health Physics Journal article ("Licensee Over-Reliance on Conservatisms in NRC Guidance Regarding the Release of Patients Treated with 131I", Health Phys. 93(6):667– 677; 2007) and our web page on the subject, treatment of patients as unshielded point sources, with use of radioactive decay as the only means of removal of activity from the body, is an overly conservative method. This is intuitively obvious, and has been confirmed by measured data in a number of cases. In this section, we provide a more realistic approach to the problem, based on methods in the HPJ paper cited above. Here the terms are:

  16. Occupancy factor = fraction of time exposed individual is assumed to be within the average distance chosen, F1 = fraction of total administered activity associated with effective half-time Teff-1, F2 = fraction of total administered activity associated with effective half-time Teff-2.

  17. 131I-Sodium Iodide (NaI) - Hyperthyroid PatientsOccupancy Factor: 0.25F1 (extra-thyroidal): 0.2F2 (thyroid): 0.8Teff-1 (extra-thyroidal): 0.32 daysTeff-2 (thyroid): 5.2 daysActivity: 20 (mCi) Average distance (m): 1 • OK CLEAR

  18. Total dose estimated for this exposure: For exposure to 20 mCi of I-131 radiation to an individual at 1 meters, the estimated total amount of radiation received is 1.6 mSv or 1.6e+2 mrem. Input data: Occupancy Factor =0.25, F1=0.2, F2=0.8, Teff1=0.32 days, Teff2=5.2 days. This might have occurred due to a uniform whole body exposure of 194 days of exposure to natural background radiation.

  19. 2. 131I-Sodium Iodide (NaI) - Thyroid Cancer PatientsOccupancy Factor: 0.25F1 (extra-thyroidal): 0.95F2 (thyroid): 0.05Teff-1 (extra-thyroidal): 0.32 daysTeff-2 (thyroid) 7.3 daysActivity (mCi): 250Average distance (m): 1 OK Clear

  20. Total dose estimated for this exposure: For exposure to 250 mCi of I-131 radiation to an individual at 1 meters, the estimated total amount of radiation received is 2.6 mSv or 2.6e+2 mrem. Input data: Occupancy Factor =0.25, F1=0.95, F2=0.05, Teff1=0.32 days, Teff2=7.3 days. This might have occurred due to a uniform whole body exposure of 316 days of exposure to natural background radiation.

  21. 3. Other Patient Release Calculations: If we have a patient with activity from any radionuclide study, we can obtain the dose by treating the subject as a 2 m line source of radiation. The best calculation will be made by using an effective half-time for estimating the cumulative exposure. A more conservative calculation will result from using just the radionuclide physical half-life. You can enter either below.

  22. [drop-down box for radionuclide choice: Sm-153]Activity (mCi): 100Average distance (m): 1Occupancy: 0.25Half-time (days): 1.93

  23. OKCLEARTotal dose estimated for this exposure: For exposure to 100 mCi of Sm-153 radiation with a 1.93 day half-time to an individual at 1 meters, and an occupancy of 0.25, the estimated total amount of radiation received is 0.75 mSv or 75 mrem. This might have occurred due to a uniform whole body exposure of 91 days of exposure to natural background radiation.

  24. Note that this is an overestimate for at least two reasons. We assumed that all the Sm-153 went to bone, when usually around 35% is rapidly excreted by the kidneys. We also assumed that the specific gamma ray constant is the same as the humanized gamma ray constant, when in fact self-absorption and assuming a line source at one meter would reduce it from 0.44 to about 0.24, a factor of 0.5.

  25. Section II. Other SituationsHere we offer a tool that allows you to calculate doses for exposure to radioactive patients or other sources for fixed periods of time. See the examples below for ways that this might be used. This section uses an unshielded, point source approximation. NOTE - the time entered here is in hours, not days. Assume a patient is taking a cab home after therapy.Choose radionuclide and enter study data. Hit 'OK' when the data are ready: [Radionuclide drop-down box; I-131]

  26. Activity (mCi):200Average distance (m): 2Time (hours): 1OK CLEARTotal dose estimated for this exposure: For exposure to 200 mCi of I-131 radiation for 1 hr of an individual at 2 meters, the estimated total amount of radiation received is 0.11 mSv or 11 mrem. This might have occurred due to a uniform whole body exposure of 13 days of exposure to natural background radiation.

  27. Note that this estimate is high because the specific gamma ray constant is used instead of the humanized gamma ray constant. The humanized gamma ray constant is 0.6 x the specific gamma ray constant. (0.6)(11 mrem)=6.6 mrem, which is a more realistic estimate to the cab driver.

  28. Gamma Ray ConstantsThe gamma ray constant has units of R/hr per mCi at 1 cm. The specific gamma ray constant assumes an unshielded point source. The humanized gamma ray constant takes account of the shape and shielding of the human body.

  29. Diagnostic Nuclear Medicine Applications This includes biokinetic models and dosimetry estimates for diagnostic radiopharmaceutical procedures. Click here to view an Excel spreadsheet with all of the dose estimates and kinetic models for many pharmaceuticals, for adults and children between 1 and 15 years of age.

  30. The Pregnant Patient An area of particular concern in nuclear medicine is the pregnant or potentially pregnant patient. A 1997 document in the Health Physics Journal Russell JR and Stabin MG, Sparks RB and Watson EE. Radiation Absorbed Dose to the Embryo/Fetus from Radiopharmaceuticals. Health Phys 73(5):756-769, 1997) gave estimates of fetal dose from over 80 radiopharmaceuticals, based on some standardized kinetic models (not necessarily identical to those shown on this web site) and, in some cases, including knowledge of the amount of radiopharmaceutical crossover, as measured in animal or human studies. To see a copy of two summary tables from that document, including a few sample calculations, click here.

  31. 1) Fetal thyroid dose - if radioiodine is administered to a woman who has passed about 10-13 weeks of gestation, the fetal thyroid will have been formed, and this tiny organ concentrates the iodine which crosses the placenta. Evelyn Watson calculated doses to the fetal thyroid per unit activity adminstered to the mother (Watson EE. Radiation Absorbed Dose to the Human Fetal Thyroid. In: Fifth International Radiopharmaceutical Dosimetry Symposium. Oak Ridge, Tennessee: Oak Ridge Associated Universities, pp 179-187, 1992). Her results are presented here (the doses are in mGy to the fetal thyroid per MBq administred to the mother): [mGy/MBqx3700=mrad/mCi]

  32. 2) The hyperthyroid patient- fetal dose has not been well established for patients whose iodine kinetics differ from the standard model for I-131 NaI. In early pregnancy (when most of these exposures should occur, as the therapy will be clearly contraindicated in patients known to be pregnant), values from a 1991 Journal of Nuclear Medicine article (Stabin MG, Watson EE, Marcus CS and Salk RD, Radiation dosimetry for the adult female and fetus from iodine-131 administration in hyperthyroidism, J Nucl Med 32:808-813, 1991) should serve well.  Their estimates were (doses are in mGy/MBq administered): "Fast" thyroid uptake meant an uptake half-time of 2.9 hours, "normal" meant a half-time of 6.1 hours.

  33. 3) The athyroid patient-  In thyroid cancer patients, I-131 NaI is often given to patients whose thyroids have been mostly removed surgically. There may be a remnant of thyroid tissue, and/or some thyroid cancer metastases around the body, but usually a large amount of activity is given (enough to destroy all remaining thyroid tissue and the mets). In a study involving a few athyroidic subjects (Rodriguez M. Development of a kinetic model and calculation of radiation dose estimates forsodium-iodide-131I in athyroid individuals. Master’s Project, Colorado State University, 1996.) it was found that the kinetics could be well characterized by treating the iodine not taken up by the thyroid by the normal kinetics of urinary bladder excretion (6.1 hour half-time). Using these assumptions, and assuming that the other normal soft tissue uptakes occur, and using Russell’s results for fetal residence times (here it seems reasonable to assume that the standard kinetic model for maternal-fetal exchange of iodine would be similar to the euthyroid case), we obtain the following dose estimates: Again, the dose estimates in later pregnancy are not likely to be of interest very often, as this kind of therapy should not be carried out on a pregnant woman.

  34. 4) Post administration conception - An unusual kinetic picture sometimes arises when conception occurs after the iodine has been administered. In this case, the iodine has already started to wash out of the body, and whatever iodine is left will irradiate the embryo. This problem was studied recently (Sparks and Stabin. Fetal radiation dose estimates for I-131 sodium iodide in cases where accidental conception occurs after administration. Presented at the Sixth International Radiopharmaceutical Dosimetry Symposium held May 7-10, 1996 in Gatlinburg, TN; Oak Ridge Associated Unversities, 1999, A. Stelson, M. Stabin, R. Sparks eds, pp 360-364); the results can be viewed by clicking here

  35. The Breastfeeding Patient If a patient who is breastfeeding is administered a radiopharmaceutical, we are interested in how long we should interrupt breast feeding (if at all) to protect the nursing infant. This subject has been studied by several authors. Most recently, a review was published in the Journal of Nuclear Medicine (Volume 41, pages 863-873, 2000). You can read the abstract here Click here to see a table with the main recommendations.

  36. Therapy Applications In therapeutic situations, even though there are standardized models for radiopharmaceutical kinetics available, it is far more important that individual-specific kinetics and dose conversion factors be applied to as great an extent as possible. This is a very complex procedure, involving calibration of medical imaging equipment, design of biokinetic studies, gathering and reduction of data, selection of models from which to extract DCFs, modification of the DCFs for individual patients, and other considerations. The RADAR site has some general documents for download to help in this area, and RADAR members are also available for consulting on this subject.

  37. Radiation Risk Consent Form LanguageVanderbilt University in Nashville, TN has developed some nice "boilerplate" language that can be used in patient consent forms for research studies involving radiation exposures, and has graciously agreed that we can share it with you on the RADAR. Click here to get your electronic mitts on a copy of this.

  38. Another goody cooked up by the folks on the Vanderbilt University Safety Committee is a table of values for doses from x-ray and CT sources, as found in the literature, linked to the patient consent form language discussed on the Nuclear Medicine Internal Dose page. See if you-like-a: External Medical Dose Table

  39. AddingDoses from Multiple Procedures:This form gives radiation dose estimates for certain radiographic and nuclear medicine procedures, based on literature reported values. Individual organ doses and total body effective doses are given for these specified examinations, and some combinations of examinations. In addition, a short statement is generated, which may be useful as part of a patient consent form document, explaining the radiation doses as numerical values and as equivalent days of exposure to natural background radiation.

  40. To use this form: Select the radiologic examinations you wish to employ from the drop-down lists. You may choose up to three radiographic exams (x-ray or CT) and two nuclear medicine exams. You can select studies from more than one major category. Fluoroscopic exams are less straightforward; other literature should be consulted for guidance. You may also enter the number (N) of each type of study in the small boxes to the left of the drop-down lists. This is optional; if you enter nothing, one study will be assumed to be done.

  41. For nuclear medicine studies, default values for the administered radioactivity of the various exams are supplied automatically. You can supply your own value for administered radioactivity (in millicuries), if you know it to be different by entering the new value in the box immediately to the right of the drop-down list. To accept the default values, just leave default values supplied unchanged. For example, the default value for administered radioactivity for a "Tc-99m Macro aggregated albumin (MAA)" is 4 millicuries; this value will appear in the box if you choose this scan.

  42. If your protocol uses a maximum of 2 millicuries, select "Tc-99m Macro aggregated albumin (MAA)" in the drop-down list, delete the "4" and enter "2" in the box to the right of the "Tc-99m Macro aggregated albumin (MAA)" selection. For a rough Spanish translation of your risk statement, check the box provided. When everything looks good, push the "OK" button. If you need to, push the "Clear" button and try again.

  43. I have chosen a F-18-FDG study with CT, for a research application.Total effective dose: 7.03 mSv or 703 mrem This research study involves exposure to radiation from a CT chest/abdomen/pelvis - axial, F-18 Fluorodeoxyglucose. This radiation exposure is not necessary for your medical care and is for research purposes only. The total amount of radiation that you will receive in this study is about 7.03 mSv or 703 mrem, and is approximately equivalent to a whole body exposure of 855 days (2.343 years) of exposure to natural background radiation. This use involves minimal risk and is necessary to obtain the research information desired.

  44. Using RADAR makes you BRILLIANT!Using RADAR is…..

  45. A piece of cake!

More Related