ML21068A410
| ML21068A410 | |
| Person / Time | |
|---|---|
| Issue date: | 03/16/2021 |
| From: | Advisory Committee on the Medical Uses of Isotopes |
| To: | |
| Jamerson K | |
| References | |
| Download: ML21068A410 (70) | |
Text
Advisory Committee on the Medical Uses of Isotopes March 16, 2021
MEETING AGENDA ADVISORY COMMITTEE ON THE MEDICAL USES OF ISOTOPES March 16, 2021 Virtual Meeting NOTE: Sessions of the meeting may be closed pursuant to 5 U.S.C. 552(b) to discuss organizational and personnel matters that relate solely to internal personnel rules and practices of the ACMUI; information the release of which would constitute a clearly unwarranted invasion of personal privacy; information the premature disclosure of which would be likely to significantly frustrate implementation of a proposed agency action; and disclosure of information which would risk circumvention of an agency regulation or statute.
TUESDAY, MARCH 16, 2021 OPEN SESSION
- 1. Opening Remarks C. Einberg, NRC Mr. Einberg will formally open the meeting and Mr. Williams will provide K. Williams, NRC opening remarks.
- 2. Old Business K. Jamerson, NRC Ms. Jamerson will review past ACMUI recommendations and provide NRC responses.
- 3. Extravasations in Nuclear Medicine J. van der Pol, MD, Dr. Jochem van der Pol will provide an overview of his study on the Maastricht 10:00 - 12:30 consequences of radiopharmaceutical extravasation and therapeutic University Medical interventions. Centre
- 5. Patient Release Evaluation of Emerging Brachytherapy Sources K. Tapp, PhD, NRC Dr. Tapp will provide an overview of the current status of the NRCs evaluation of patient release following administration of new emerging brachytherapy sources.
12:30 - 1:00 BREAK
- 6. ACMUI Reporting Structure K. Jamerson, NRC Ms. Jamerson will provide an overview of the current reporting structure.
Members will discuss the reporting structure of the Committee and provide feedback to the NRC.
- 7. Calibration Procedures for Brachytherapy Sources L. DeWerd, PhD, Dr. Larry DeWerd will provide a presentation on the calibration procedures University of for existing brachytherapy sources and considerations for emerging manual Wisconsin brachytherapy sources.
1:00 - 3:00
- 9. Administrative Closing K. Jamerson, NRC Ms. Jamerson will provide a meeting summary and propose dates for the fall 2021 meeting.
3:00 ADJOURN
2019 ACMUI RECOMMENDATIONS AND ACTION ITEMS Target Completion ITEM DATE STATUS Date for NRC Action The ACMUI endorsed the Appropriateness of Medical Event Partially 17 Reporting Subcommittee report and the recommendations 9/10/2019 Open Summer/Fall 2021 Accepted provided therein.
The ACMUI endorsed the Evaluation of Extravasations Subcommittee Report, as amended, to note that under future 18 revisions to Part 35 rulemakings, extravasations be captured as 9/10/2019 Accepted Open Summer/Fall 2021 a type of passive patient intervention in the definition of patient intervention.
1
2020 ACMUI RECOMMENDATIONS AND ACTION ITEMS Target Completion ITEM DATE STATUS Date for NRC Action The ACMUI endorsed the Patient Intervention subcommittee 4 report, as presented, and the recommendations provided 03/30/2020 Accepted Open Summer/Fall 2021 therein.
The ACMUI endorsed the Medical Event Subcommittee Report Propose 10 09/21/2020 Accepted as presented. closure As part of the Non-Medical Events report, the ACMUI recommended to the NRC staff and/or NMP to evaluate the issue of detection of short-lived medical isotopes in municipal 11 09/21/2020 Accepted Open Fall 2021 waste (waste from nuclear medicine patients that might be triggering the landfill alarms) and provide some level of guidance, best practices, or additional instructions.
The ACMUI tentatively scheduled its spring 2021 meeting for March 15-16, 2021. The alternate date is March 22-23, 2021. Propose 12 09/22/2020 Accepted Virtual or in-person meeting is TBD, as well as timing of next closure ACMUI Commission meeting.
1
Radionuclide Extravasation March 16, 2021 Jochem van der Pol Nuclear Medicine Physician Maastricht University Medical Center 1
Introduction Amsterdam Maastricht
- Jochem van der Pol
- Nuclear Medicine Physician (2017)
- Maastricht University Medical Center
- Clinical areas of interest: neurological, oncological and cardiovascular imaging
- Scientific areas of interest: cardiovascular nuclear imaging 2
Extravasation Literature Study
- Discussion following a case of 99mTctracer extravasation
- Protocol: how to act in case of extravasation
- No guidelines Dutch Association of Nuclear Medicine (NVNG),
EANM, SNMMI, DGN (Germany)
- find literature 3
Extravasation Literature Study
- Local protocol: how to act in case of extravasation?
- No guidelines Dutch Association of Nuclear Medicine (NVNG), EANM, SNMMI, DGN (Germany)
- extensive literature search and analysis, why not publish 4
Extravasation Literature Study
- Local protocol: how to act in case of extravasation?
- Can extravasation cause deterministic effects, such as skin burn?
- Should you apply any kind of therapy?
- Cooling or warming?
- Should you perform dosimetry and how?
5 Methods
- Extensive literature search in Pubmed and Embase
- Search strings:
6
Methods
- Merging of results Embase and Pubmed
- Screening of abstracts by two persons
- If abstract mentioned humane radioactive tracer extravasation, publication was marked for further analysis.
- Marked publications were retrieved from online sources, university libraries or by tracking authors and subsequent email correspondence
- Bibliographies were screened to complement database search 7
Methods
- Data was extracted from publications:
- Number of cases
- tracer involved
- Injection place
- Estimated extravasated volume and activity
- Estimated tissue dose
- Follow up duration and method
- Applied medical interventions
- Advised/discouraged 8
Results
- 4523 abstracts (1123 in both search engines)
- Rejected abstracts
- 1012 animal studies
- 2622 extravasation/infiltration of substance other than radiopharmaceutical
- 196 Extravasation as a pathological finding not associated with injection of radiopharmaceutical (ie 99mTcMAG3 excretion
- 603 Radionuclide use for other purposes (s.a. radio immunoassays) 9 Results
- Full text retrieval 81 publications
- After screening references, a further 27 publications were retrieved (108)
- 44 publications about radiopharmaceutical extravasation:
- 37 diagnostic
- 8 therapeutic
- 10 expert opinion based publications 10
Results: Diagnostic Tracer Extravasations 11 Results: Diagnostic Tracer extravasations Wagner, T., et al. (2011). "A falsepositive finding in therapeutic evaluation:
hypermetabolic axillary lymph node in a lymphoma patient following FDG extravasation." Nucl Med Rev Cent East Eur 14(2): 109111.
12
Results: Diagnostic Tracer extravasations Wagner, T., et al. (2011). "A falsepositive finding in therapeutic evaluation:
hypermetabolic axillary lymph node in a lymphoma patient following FDG extravasation." Nucl Med Rev Cent East Eur 14(2): 109111.
13 Results: Diagnostic Tracer extravasations Alibazoglu, H., et al. (1998). "Injection artifact on FDG PET imaging." Clinical Nuclear Medicine 23(4): 264265.
14
Results: Diagnostic Tracer Extravasations
- Evaluation 190 FDG PET scans
- 39 (21%) with visible focus injection site
- 36 less than 1% injected dose
- 3 with 3,0%, 7,7% 17,5%
- Percent change in SUV max ranged from 021%
Hall N., Z. J. (2006). "Impact of FDG extravasation on SUV measurements." J Nucl Med 47(suppl 1): 115P. (SNMMI 2006 Poster presentation) 15
- Evaluation 400 FDG PET scans
- 42 (10,5%) with noticable extravasation Results: Diagnostic Tracer extravasations
- 5 cases with repeat studies without therapy
- Mediastinal SUV change 9,3%
- Hepatic SUV change: 11,7%
Osman, M. M., et al. (2011). "FDG Dose Extravasations in PET/CT: Frequency and Impact on SUV Measurements." Front Oncol 1: 41.
16
Results: Diagnostic Tracer Extravasations 17 Results: Diagnostic Tracer extravasations Boxen, I. (1985). "Inadvertent lymphoscintigraphy?" Clin Nucl Med 10(1): 2526 18
Results: Diagnostic Tracer Extravasations 19 Results: Diagnostic Tracer extravasations
- 34MbqIodocholesterol
- After 13 days erythematous pruritic patch
- Complete tracer retention after 7 days Breen, S. L. and A. A. Driedger (1991). "Radiation injury from interstitial injection of iodine131iodocholesterol." J Nucl Med 32(5): 892.
20
Results: Diagnostic Tracer Extravasations Anon. (1988). "European system for reporting of adverse reactions and drug defects:
Third report 19841985." European Nuclear Medicine Society News Letter(9): 487490.
21 Results: Therapeutic Tracer Extravasations Anon. (1988). "European system for reporting of adverse reactions and drug defects:
Third report 19841985." European Nuclear Medicine Society News Letter(9): 487490.
22
Results: Therapeutic Tracer Extravasations 23 Results: Therapeutic Tracer Extravasations 24
Results: Therapeutic Tracer extravasations Anon. (1988). "European system for reporting of adverse reactions and drug defects: Third report 19841985." European Nuclear Medicine Society News Letter(9): 487490.
25 Results: Therapeutic Tracer Extravasations Anon. (1988). "European system for reporting of adverse reactions and drug defects: Third report 19841985." European Nuclear Medicine Society News Letter(9): 487490.
26
Conclusions:
Literature Study
- Extravasation of tracers is common
- No adverse effects of 18F, 99mTc, 123I and Ga68 reported >
no reason to assume extravastion of these tracers has clinical significance.
- Sporadic reports of other diagnostic tracers have described soft tissue lesion
- Multipele reports of severe adverse events following therapeutic tracer extravasation.
27 What is the frequency of extravasations in Nuclear Medicine and what criteria should be used for identifying an extravasation (visualization, % injected dose, etc.)?
- Frequency: unknown
- MUMC 20072018
- Reported radionuclide extravasations 3 (FDG) (est.
6.000/year)
- Reported contrast extravasation: 91 (est. 50.000/year)
- Literature
- No national registration 28
What is the frequency of extravasations in Nuclear Medicine and what criteria should be used for identifying an extravasation (visualization, %
injected dose, etc.)?
- What criteria:
- Clinical: painful injection, swelling and redness or palor
- %Injected dose
- Diagnostic: doesnt seem to be relevant.
- Quality is a parameter any nuclear medicine physician should monitor.
- If quality is below standards, consider repeat study, always perform internal registration for quality improvement (irrespective of the cause)
- Therapeutic: any extravasation noted at any timepoint should be adequately treated and registered, irrespective of dose 29 What is the appropriateness of reporting extravasations that result in a certain tissue dose threshold (0.5 Sv) as a Medical Event (Adverse Event)?
- How will the dose be calculated?
- Erythema threshold 2.5Sv 30
How does the European community address reporting of extravasations?
- No European legislation The EU does not define health policies, nor the organisation and provision of health services and medical care. Instead, its action serves to complement national policies and to support cooperation between member countries in the field of public health.
31 How does the European community address reporting of extravasations?
- Dutch legislation:
- No definitions or mentioning of (radiopharmaceutical) extravasation
- Different definitions of adverse events:
- Complications
- Incidents
- Calamity 32
How does the European community address reporting of extravasations?
- Complication: an unintentional and undesired outcome during or following the actions of a medical care provider, which demands adaptation of the medical procedure of causes irreparable damage
- Worked according to medical standards
- Unintended oucome
- Incident: An unintentional or unexpected event, that is related to quality of healthcare and that could have led to the death of a client [patient] or serious harmful consequences for a client [patient]
- Calamity: An unintentional or unexpected event, that is related to quality of healthcare and that has led to the death of a client [patient] or serious harmful consequences for a client [patient]
33 How does the European community address reporting of extravasations?
- When do we report to healthcare authorities:
- Calamities
- Incidents and complications are reported and registered locally, as advised by healthcare professional societies.
- unless when the nature is not clear and calamity is not ruled out Authorities advise on event.
34
What are the issues/challenges in determining the tissue dose from an extravasation?
Geometry Point source not realistic, distance > 10 times diameter Disc shaped source, complex mathematics Activity concentration is a great factor in dose calculations 35 What are the issues/challenges in determining the tissue dose from an extravasation?
Geometry Point source not realistic, distance > 10 times diameter Disc shaped source, complex mathematics Activity concentration is a great factor in dose calculations 36
What are the issues/challenges in determining the tissue dose from an extravasation?
Geometry Point source not realistic, distance > 10 times diameter Disc shaped source, complex mathematics Activity concentration is a great factor in dose calculations What about cystic distribution?
Homogenity of distribution?
Real world: very complex geometry with evolving boundaries 37 What are the issues/challenges in determining the tissue dose from an extravasation?
Biological half life Probably less relevant for short half life PET tracers More relevant for tracers with longer half life Dynamic behaviour: multiple acquisitions 38
What personnel training, qualifications, and quality assurance should be in place to monitor/prevent for extravasations in medicine?
- Technician
- Properly trained for obtaining IV access
- (Special exception to perform medical procedure)
- Nuclear medicine physician/Radiologist
- Always check image quality. If not adequate: repeat study!
- Signs of (significant) tracer accumulation near injection site?
39 What personnel training, qualifications, and quality assurance should be in place to monitor/prevent for extravasations in medicine?
- Radiation safety officer/quality officer
- Keep local registration of extravasation cases
- Goal: quality improvement
- Train technicians/NM physicians with bad track records 40
Acknowledgements Prof. F. Mottaghy Dr. S. V l Prof. J. Bucerius Prof. M. de Haan l Dr. R. Wierts 41
OPEN FORUM No Handout
Patient Release Considerations Associated with Temporary Brachytherapy Devices Katie Tapp, PhD Medical Radiation Safety Team March 16, 2021 1
Overview
- This presentation will provide an overview of
- Temporary implant devices,
- The scope of staffs evaluation of patient release for those with temporary implants,
- The many regulatory questions the staff intends to answer through its evaluation,
- Next steps.
2 1
Patient Release Regulations (10 CFR 35.75)
- A licensee may authorize the release from its control of any individual who has been administered implants containing byproduct material if the dose to any other individual from exposure to the released individual is not likely to exceed 5 mSv (0.5 rem).
- A licensee shall provide the released individual with instructions on actions recommended to maintain doses to other individuals as low as is reasonably achievable if the dose to any other individual is likely to exceed 1 mSv (0.1 rem).
3 Patient Release Regulations (10 CFR 35.75)
- Before 2002, patient release regulations only allowed release of permanent implants
- In 2002, the regulations were amended to allow patients to be released with all types of implants if the dose limits were met.
- Regulatory Guide 8.39 does not provide guidance for temporary implants.
4 2
Temporary Implants
- Temporary implants are expected to be removed from the patient at a specific time to deliver the prescribed dose.
- Examples of temporary implants include:
- Brachytherapy Seeds
- Emerging brachytherapy devices, including:
- Alpha DaRT
- CivaDerm 5
- Plaques are temporarily attached to the wall of the eye
- The plaque contains brachytherapy sources and shielding on the backside
- Licensed under 10 CFR 35.400 and patients released under 10 CFR 35.75.
6 3
Brachytherapy Seeds
- Ir192 seeds have been used in ribbons for temporary implant brachytherapy.
- Many of these patients stay in the hospital during treatment.
- I125 seeds are also used for radioactive seed localization. These patients are released following implantation and return to have the seeds excised.
7 Alpha Dart
- Alpha DaRT is the first manual brachytherapy device which uses diffusing alpha emitting radiation for therapeutic treatment.
- Alpha Dart seeds contain 224Ra.
- Inside the tumor, the source diffuses as the 224Ra atoms decay down its decay chain.
8 4
Alpha Dart (cont.)
- Currently, this therapy utilizes temporary implants but they may be used for permanent therapy in the future.
- Staff expects to provide a draft 10 CFR 35.1000 licensing guidance for the ACMUI review in early summer.
9 CivaDerm
- Temporary brachytherapy using Pd103 sources affixed to the skin surface.
- Patients will need to return to the licensee to have the sources removed.
- Sources are self shielded with a cold and hot side.
- Staff is still evaluating the licensing pathway for use.
10 5
CivaDerm (cont.)
- Sources are affixed by:
- placing on clean, dry skin
- Attached with a surgical bandage
- Secured with additional radiation shield cover
- Covered with a waterproof shield 11 Regulatory Considerations Evaluation Public Medical Lost Other Exposure Event Source Removed Incidental 12 6
Regulatory Considerations Evaluation Public Medical Lost Other Exposure Event Source Removed Incidental 13 Patient Release
- 10 CFR 35.75 states licensees may authorize the release from its control of any individual who has been administered implants containing byproduct material if the dose to any other individual from exposure to the released individual is not likely to exceed 5 mSv (0.5 rem).
- Licensees will need confidence that the source will not become dislodged, as it is possible a loose source could exceed this limit.
14 7
Public Dose Limits
- Public dose limits in Part 20 exclude exposure to individuals administered radioactive material and released under 10 CFR 35.75.
- Public dose limits do not appear to exclude dose from sources which are dislodged from patients.
- Further evaluation is ongoing to determine if public dose limits listed in Part 20 apply to sources dislodged from patients.
15 Public Exposure Potential
- Licensing evaluations prior to authorizing release of patients with temporary implants must consider:
- Ease of which a source could become dislodged, and
- Public exposure potential Dose rate for maximum activity sheet for CivaDerm Dose rate at 5 cm Dose rate at 100 (mrem/hr) cm (mrem/hr)
Cold 968 2.52 Hot 23,883 31.23 16 8
Regulatory Considerations Evaluation Public Medical Lose Other Exposure Event Source Removed Incidental 17 Licensee Evaluation
- 10 CFR 35.41 requires licensees to have procedures to ensure high confidence that each administration is in accordance with the written directive.
- These procedures must address the following items:
- Verifying the administration is in accordance with the written directive, and
- Determining if a medical event has occurred.
18 9
Medical Event
- If a source is dislodged or if a patient does not return at a specified time, it could lead to a medical event under 10 CFR 35.3045:
- (a.1.i) a dose that differs from the prescribed dose by more than 0.5 Sv (50 rem) to an organ or tissue and the total dose delivered differs from the prescribed dose by 20 percent or more, or 19 Medical Event (cont.)
- (a.1.iii) A dose to the skin or an organ or tissue other than the treatment site that exceeds by
- (A) 0.5 Sv (50 rem) or more the expected dose to that site from the procedure if the administration had been given in accordance with the written directive prepared or revised before administration; and
- (B) 50 percent or more the expected dose to that site from the procedure if the administration had been given in accordance with the written directive prepared or revised before administration.
20 10
Patient Intervention
- Patient intervention means actions by the patient or human research subject, whether intentional or unintentional, such as dislodging or removing treatment devices or prematurely terminating the administration.
- If the source comes off due to an action by the patient, it could be considered patient intervention and not a medical event.
- More guidance is needed.
21 Regulatory Considerations Evaluation Public Medical Lost Other Exposure Event Source Removed Incidental 22 11
Lost Source
- If the licensee is unable to retrieve a temporary source, the source could be considered lost.
- 10 CFR 20.2201 requires licensees to report loss of licensed material above specified limits.
- Telephonic reports need to be made within 24 hours2.777778e-4 days <br />0.00667 hours <br />3.968254e-5 weeks <br />9.132e-6 months <br /> or 30 days depending on the activity.
23 Lost Source (cont.)
- Written reports are required 30 days after initial telephone report and need to include:
- Description of circumstances
- Statement of probable disposition
- Exposure of individuals
- Actions taken to try to recover the material
- Procedures to prevent another lost source 24 12
Brachytherapy Source Accountability
- 10 CFR 35.406 requires that a licensee maintain accountability at all times for all brachytherapy sources in storage or use.
- If a source is lost, the licensee would not be able to account for the source or be able to complete the record required per 10 CFR 35.2406 for temporary implants.
25 Regulatory Considerations Unreturned Source Lost Medical Public Other Source Event Exposure Removed Incidental 26 13
Other Considerations
- Brachytherapy source accountability requires licensees to record the location of use for temporary implants per 10 CFR 35.2406.
- As the implants are temporary, the written directive will need to include dose unlike permanent brachytherapy implants which uses source strength.
27 Next Steps
- Staff will continue to evaluate these regulatory questions regarding release of patients with temporary implants.
- Staff will provide ACMUI with the results of this evaluation and any associated licensing guidance documents.
- Staff will be providing AMCUI with draft 10 CFR 35.1000 licensing guidance for Alpha Dart.
28 14
- CFR - Code of Federal Regulations
- I125 - iodine125
- Ir192 - iridium192 29 15
ACMUI Reporting Structure Kellee Jamerson, ACMUI Coordinator Medical Radiation Safety Team March 16, 2021 1
Outline
- Current Reporting Structure
- Annual Review
- Meetings
- Discussion 2
2 1
Current Reporting Structure The Commission EDO Margaret Doane Director, NMSS John Lubinski Director, MSST Kevin Williams ACMUI Chief, MSEB Christian Einberg 3
3 Annual Review In September 2012, the ACMUI recommended to have an annual review of reporting structure.
4 4
2
Meetings Two meetings at Headquarters each year
- March/April
- September/October Approximately 2-3 teleconferences (as needed) 5 5
ACMUI Discussion 6
6 3
Points of Contact
- Kevin Williams - MSST Director
- Kevin.Williams@nrc.gov
- Christian Einberg - Designated Federal Officer (DFO), Chief, MSEB
- Christian.Einberg@nrc.gov
- Kellee Jamerson - DFO, ACMUI Coordinator
- Kellee.Jamerson@nrc.gov 7
7 Acronyms
- DFO - Designated Federal Officer
- EDO - Executive Director for Operations
- MSST - Division of Materials Safety, Security, States, and Tribal Programs
- MSEB - Medical Safety and Events Assessment Branch
- NMSS - Office of Nuclear Material Safety and Safeguards 8
8 4
Professor Larry DeWerd, PhD, FAAPM Medical Radiation Research Center Dept of Medical Physics (SMPH)
University of Wisconsin Madison, WI 1
The desirable quantity is absorbed dose to water. This quantity is determined from AAPM TG 43 The calibration quantity is air kerma strength which is converted with a dose rate constant Note that the quantity activity is NOT used for brachytherapy sources.
Air kerma strength is quantity of radiation emitted from source after cladding 2
1
Photon Source: Air kerma strength - symbol Sk. Given as unit U where U[=]Gy- m2/h.
Values of Sk can be up to 260 U.
Beta sources:
Absorbed dose rate in water at a depth done with an extrapolation chamber (usually 2 mm)
I will cover photon sources because of time constraints and then some future calibrations 3
Low energy photon sources (both high and low dose rate)
High energy photon sources (used for High Dose rate brachytherapy - both high and low dose rate)
Beta brachytherapy sources (used for Intravascular Brachytherapy for prevention of restenosis, eye plaques for tumors and Ophthalmic Applicators used to treat eye)
Majority use in Brachytherapy is Low energy -
low dose rate and High energy - high dose rate 4
2
Energy Dose Rate Type Primary calibration standard at NIST Low Low LDR seeds, WAFAC 125I, 103Pd, 131Cs High High HDR Ion Chamber afterloaders 7Distance (192Ir) Technique 5
- 1. Use of a free air chamber (WAFAC) for Low energy Low Dose sources
- 2. Use of a thimble chamber in air (UW) for High energy High dose sources
- 3. Use of an extrapolation chamber for beta sources.
6 3
To provide effective treatment to neoplastic disease must quantify dose to tissue of interest Standard should be specified by a clinically relevant metric Presently this quantity is air-kerma strength for photon sources. In Europe, the quantity is Reference Air Kerma Rate (RAKR)
The quantity is Energy deposited per unit mass (i.e.
J/kg) at a distance in vacuo 7
Air Kerma Strength (Gym2/hr)
Actual characterization of source output in terms of the dose delivered to air. Related to exposure primarily by W/e, which is the average energy required to produce an ion pair in dry air.
Endorsed by the AAPM for use in treatment planning protocols and adopted in TG 43.
8 4
(r,) ,
SK is air kerma strength G is geometry factor is dose rate constant g is radial dose function F is anisotropy function 9
Air Kerma Strength - Determined in clinic by a well chamber traceable to NIST Dose rate constant, , measured by TLD and Monte Carlo calculated.
Radial dose function, g(r), and anisotropy function, F (r,) are all measured by TLD and calculated by Monte Carlo. G is the geometry factor All are consensus values.
10 5
11 For x-ray sources: standard is at 50 cm in air
- equation modified somewhat Lamperti FAC used 12 6
Medical physicist needs to calibrate source or if multiple sources at least 10%
of the sources For LDR sources, there have been examples of dead seeds, some seeds with twice the output of the others in the batch.
Dont just trust what manufacturer has sent. Measure it!!!!
Calibration differs among sources because of cladding - 5% differences 13 14 7
- NIST has transferred calibrations to ADCLs for LDR sources. all ADCL Secondary Laboratories fall within + 0.6%
- ADCLs have traceability to NIST.
Beta sources: All ADCL secondary Laboratories fall within + 2%
Uncertainties for Proficiency tests Gamma sources: + 2% (k=2)
Beta sources: + 3% (k=2) 15 Palladium 103 introduced in 1987 with NO NIST standard - used a Cd source Manufacturer changed calibration using a different Cd source, self-shielding of the source encapsulation was different This resulted in a sudden 9% shift in calibration. Manufacturer communicated this by letter to users in 1997 16 8
17 Palladium 103 dose has changed many times.
Manufacturer caused 9% shift in calibration and dose to patient.
Shows importance of a standard and that physicists calibrate the sources.
18 9
Clinical calibration using a well chamber.
The insert is part of the calibration.
The chambers and methodology for brachytherapy calibrations is different from Nuclear Medicine and PET, which use a dose calibrator.
A dose calibrator reads in activity not dose or Air kerma Also energy dependence of a dose calibrator is more severe than vented well chamber 19 The quantity used for Nuclear Medicine and PET is activity and the unit is Bq (Curies).
This quantity is not Dose!
An activity may be administered by syringe but to know the dose received by a given tissue is different.
Expansion on this point when look at future 20 10
ADCL Calibrated Well chamber: Provides the most convenient, accurate and precise measure of source strength.
Know the characteristics of chamber, whether it can measure LDR or HDR or both. What is between the source and the collector of the well?
Pressurized chambers (sealed) can leak 1% per year Use an electrometer that can measure a low enough signal without leakage for LDR sources 21 If a single seed is used Rdg1 is obtained If multiple seeds of the same strength are measured, the reading is RdgM=n Rdg1 If average strength per seed is needed, the total train air kerma strength is divided by the number of seeds, n.
If strands of different strength an average is obtained.
22 11
Because of variation of thicknesses of needles (caused by manufacturer tolerances) sources have a 15% variation by needle.
Sources cannot be measured in Needles 23 Energy response of vented chambers is not severe compared to pressurized chambers The following curve indicates why each energy and each chamber requires calibration 24 12
25 cal coeff HDR 1000 1.2 1 1 0.899 0.885 0.889 0.8 Normalized Response 0.6 0.4 0.2 0
23 27 397 660 Energy 26 13
Higher energy sources require other techniques FAC are too big to use.
A chamber with a known volume can be used or a chamber with a flat and calibrated energy response 27 NIST does not offer a primary HDR 192Ir source calibration 7-Distance in-air technique first proposed at the University of Wisconsin by Goetsch et al. in 1991 - this is after the chamber calibration Allows ADCLs to provide NIST traceable calibrations for HDR 192Ir NIST traceability is provided by an interpolated chamber correction factor 28 14
29 Establishing NIST traceability requires two steps calibration of ion chamber using that chamber to calibrate source.
Known volume chamber used by NPL.
If the chamber used has a flat energy response, 2 points interpolated to the weighted average energy is all that is needed.
30 15
The ionization chamber is calibrated at two energy points to interpolate to the weighted average energy of the HDR 192Ir source, which is approximately 397 keV.
The two points are M250 (x-ray) and Cs-137 with interpolation.
The same buildup cap with thickness sufficient to provide CPE for highest energy must be used for both NIST calibrations 31 Mainegra-Hing and Rogers argued that the interpolation should be based upon an interpolation proportional to ion chamber response. Thus, The energy for 192Ir is 397 keV The second aspect is to calibrate the source at distances 32 16
33 All primary labs do a variation on the 7-distance technique.
NPL has a known measured volume chamber Others determine their factor by interpolation Many do all 4 coordinate directions 34 17
There are 5 HDR sources on the market Monte Carlo modeling shows that there may be a difference between them.
We investigated all sources using the 7-D technique Published in Med Phys 38: 6721-6729 (2011)
UWADCL measurement was originally based on the Classic Nucletron HDR source 35 The classic Nucletron source has been measured over more than a 21 year period.
Each individual source has been compared to the other via 3 well chambers The value for the well chamber after measurement by the 7 distance technique is always within + 0.5%
36 18
HDR Source Model % difference from Working Standard Classic Nucletron 0.47 Nucletron V2 0.10 VariSource VS2000 1.13 GammaMed Plus 0.20 Flexisource 0.89 Average for all sources 0.01 37 When all source models are averaged the value is 0.01% compared to the 21 year old value.
All source models will use the same calibration factor since all agree within 1% when the uncertainty of measurement is +2%.
Comparisons with other labs (Henri - Becquerel, NPL, PTB, NRCC) within 0.5%
Summary of measurements with all sources -
statistically different but all within 1% of the mean 38 19
Half Life of 192Ir is short - replace source every 3 to 4 months.
Use 60Co have 5 years. But maintenance becomes essential Calibration still done as for HDR, known volume chamber at 7 distances. Calibration at cobalt energy Need to develop consensus values - dose rate constant, etc.
39 Targeted Radionuclide Therapy Or Targeted Radiopharmaceutical Therapy (TRT)
Alphas and betas: 224Ra, Ac, Po Present calibration in activity Prefer absorbed dose to water Difficult since alpha and betas - how much goes to the specific area desired?
40 20
Betas calibrated with an extrapolation chamber. Windowless extrapolation chamber for beta eye plaques.
I have a graduate student trying to do calibration for alphas and betas with a windowless extrapolation chamber - PhD thesis Hopefully will get Absorbed Dose to Water that would be delivered from amount of activity deposited in tissue of interest.
41 Thanks to Customers of MRRC whose calibrations support graduate research.
All graduate students and staff that I have provoked with my thoughts.
Any Questions.
42 21
OPEN FORUM No Handout
September 2021 Sunday Monday Tuesday Wednesday Thursday Friday Saturday 29 30 31 1 2 3 4 5 6 7 8 9 10 11 Labor Day Rosh Hashanah 12 13 14 15 16 17 18 Yom Kippur 19 20 21 22 23 24 25 Sukkot 26 27 28 29 30 1 2 3 4 Notes
October 2021 Sunday Monday Tuesday Wednesday Thursday Friday Saturday 26 27 28 29 30 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 Columbus Day 17 18 19 20 21 22 23 24 25 26 27 28 29 30 ASTRO Annual Meeting ASTRO Annual Meeting ASTRO Annual Meeting ASTRO Annual Meeting 31 1 Notes