WAM-A - Medical Health Physics Centennial Ballroom 300A 09:30 - 11:15
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| Chair(s): Glenn Sturchio
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WAM-A.1
09:30 Medical Radioisotope Production from Uranium and Radium AC Bakken*, Niowave, Inc.
; RN Wahlen, Niowave, Inc.; NC Johnson, Niowave, Inc.; WA Peters, Niowave, Inc.; TL Grimm, Niowave, Inc.; CH Boulware, Niowave, Inc.; AV Gelis, University of Nevada, Las Vegas
Abstract: Niowave produces high-purity alpha and beta emitting isotopes for diagnostic and therapeutic medical applications. Radioisotope production processes use a superconducting electron linear accelerator and closed loop radiochemistry cycles. During production, an electron beam impinges on a photon converter to irradiate Uranium or Ra-226 targets; this induces nuclear reactions which produce isotopes such as Mo-99 or Ac-225. Niowave then operates a closed loop radiochemical processing cycle to dissolve, extract, and purify radioisotopes of interest. The radiochemistry processes require handling of dispersible alpha, beta, and gamma emitters in solid, liquid, and gaseous forms. Once purified, isotope products are chemically and radiologically analyzed to determine purity before shipment to customers. The source materials for producing Niowave’s radioisotopes are rare; therefore, radiochemical processing includes recovery of target material for continued production. This minimizes loss and reduces the generation of radioactive waste.
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WAM-A.2
09:45 Evaluation of Radiation Exposure to Personnel in Novel Biology-Guided Radiotherapy Workflow AM Jaramillo*, UT Southwestern
; CE Pagan, UT Southwestern; I Chavarria, UT Southwestern; R Grabarkewitz, UT Southwestern; A Pompos, UT Southwestern; B Cai, UT Southwestern; S Everett, UT Southwestern; MJ Amen, UT Southwestern
Abstract: In current practice within radiation oncology, most radiation therapists do not work closely with patients who have been injected with radiotracers. During a recent clinical trial to evaluate the PET imaging component of the RefleXion PET-LINAC, the researchers set out to study the occupational radiation exposure to the radiation therapists and other staff involved in the mock Biology-guided Radiation Therapy treatment. The intent of this study was twofold: 1) to measure the current occupational radiation exposure to healthcare personnel involved in the PET-LINAC treatment procedure and estimate the potential exposure based on future workload projections, and 2) develop workflow recommendations to reduce the occupational radiation exposure to these staff members. Patient exposure rates were taken at predefined points during the treatment day, and therapist-patient interaction time was tracked. The preliminary patient population was four patients and a total of eight treatment days. After the uptake period and post voiding, the average patient exposure rate was 7.2 mR/h. The longest period the therapists spent with the patient was after the patient void and when the therapists positioned the patient on the treatment unit, an average of 9.0 minutes over the average total patient time of 16.5 minutes. The average total therapist dose for the eight treatment days was 13 mrem, and under an estimated future workload of four patients per day would be 320 mrem annually. For the nuclear medicine technologist, the extremity dose increased by 100 mrem for the eight treatment days. This would lead to an additional 2,500 mrem annual extremity dose for four patients per day. Implemented recommendations to lower the occupational radiation exposure for the nuclear medicine technologist and therapists continue to be evaluated with additional patients.
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WAM-A.3
10:00 A Health Physics Evaluation of Yb169 Brachytherapy Treatment for Cervical Cancers MR Jalbert*, Worcester Polytechninc Institute
; DC Medich, Worcester Polytechnic Institute
Abstract: As a middle-energy high dose rate (HDR) source, Ytterbium-169 (half-life 32 days, Average Energy = 92.7keV, Mode Energy = 50.9keV, Median Energy = 50.7keV) demonstrates potential to be an accessible and effective shielded brachytherapy source. A new collimated Yb-169 device, previously designed for the treatment of ocular melanoma is being adapted to treat cervical cancer. No studies have yet been conducted to measure the medical health physics impact of handling and utilizing a Yb-169 source. This study will use MCNP6 Monte Carlo Simulations to assess the potential of using localized shielding on this new Yb-169 brachytherapy device to satisfy federal safety regulations. Current HDR brachytherapy treatments, like those using Ir-192, require expensive shielding, which has been a limiting factor in the accessibility of HDR brachytherapy. The first half-value thickness of Yb169 in lead is less than 300µm. This gives Yb-169 the potential to be a cost-effective alternative, in turn granting better access to HDR brachytherapy to hospitals, especially those in under-developed communities.
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WAM-A.4
10:15 Development of Surface Contamination Action Levels for a Multistate Medical Licensee V Ram*, Mayo Clinic
; GM Sturchio, Mayo Clinic
Abstract: Mayo Clinic has broad scope radioactive material licenses in four states and it is a challenge developing single procedures due to differing state regulations. This is particularly apparent when reviewing the diverse surface contamination action levels presented in federal and state guidance. We decided to reinvent surface contamination action levels from first principles using: radionuclide radiation types, half-life, exposure geometry, exposure pathways, exposure time, and other workplace parameters. We compare the dpm cm-2 values of our model to the existing guidance and try to explain the discrepancies – not always an easy task! The next step in operationalizing the results – to facilitate usefulness in the practice – required the transformation of the dpm cm-2 values into portable radiation protection instrumentation response values (i.e., cpm). The evaluation of instrumentation response includes determination of the critical level (Lc) and the MDA for the counting system. This important step highlighted that some of the radionuclides of interest cannot be detected by routine direct reading instrumentation (i.e., pancake GM). The final product is a list of radionuclides grouped by surface contamination action levels (in order of magnitude tranches) and the associated recommended radiation protection instrumentation with instrument specific action levels.
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WAM-A.5
10:30 Feasibility of safe outpatient radio-targeted treatment in pediatric patients following administration of 131 Omburtamab for leptomeningeal disease K Prasad*, Memorial Sloan Kettering Cancer Center
; BP Chu, Memorial Sloan Kettering Cancer Center; M Bellamy, Memorial Sloan Kettering Cancer Center; N Pandit-Taskar, Memorial Sloan Kettering Cancer Center
Abstract: I-131 Omburtamab has been administered intraventricularly in 200 patients were treated under an institutionally approved study (#NCT03275402). Radiation safety precautions were tailored for individual patients enabling outpatient treatment. We hereby delineate our procedure and in-depth evidence-based recommendation for patient specific precautions. Methods: Patients were treated with 33-50 mCi of radiolabeled antibody (RIT) administer intraventricularly via ommaya reservoir, under all aseptic and radiation handling precautions. RIT was administered in the pediatric ambulatory care center (PACC). Designated rooms were set up with Herculite for contamination control and posted with radiation area signs pre-administration. Dosimeters were provided to staff involved in patient care to evaluate exposure during injection and post-administration. Post-administration exposure readings from the patient on contact, one foot and one meter were taken within the first 30 minutes and the room was surveyed at the end of the day after patient discharge. Radiation safety precaution duration was calculated using standard Regulatory Guidance recommendations and using combined exposure and whole-body clearance estimates. Measurements combined with clearance data informed patient specific precautions for 4 cohorts: <3y/o, 3-10 y/o, 10-18y/o and 18+. Results: Patient post-administration exposure measurements ranged from 0.6 - 1.7 mR/hr/mCi at 1ft, and 0.11-0.29 mR/hr/mCi at 1m. Radiation safety precautions duration ranged from 1-10 days after release for the four evaluated cohorts. The longest precautions, based on highest measured dose rates and slowest whole-body clearance, was about 78% lower than the Regulatory Guidance recommendations. Radiation exposure to staff associated with I-131 Omburtamab administration was substantially below the regulatory threshold for individual monitoring of external occupational dose. Conclusion: I-131 Omburtamab can be safely administered on an outpatient basis, with appropriate patient-based radiation safety precautions that can be reduced with use exposure and biological clearance parameters.
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WAM-A.7
10:45 Patient Specific Neutron Shielding For Electronic Device Attached To Proton Patient; Case Study R Rahimi*, INOVA Schar Cancer Institute
; M Taylor, INOVA Schar Cancer Institute; M Eblan, INOVA Schar Cancer Institute; J Fan, INOVA Schar Cancer Institute; P Wang, INOVA Schar Cancer Institute
Abstract: Proton therapy has shown dosimetric advantage over conventional radiation therapy for some disease sites; however there have been concerns on proton generated neutrons that could cause biological complications, as well as damages to electronic devices attached to patients. While in our center, INOVA Mather Proton Center, we have been investigating the proton produced neutrons, for IBA ProteusPlus PBS system, and its effect on patients, the current work is a case study where one of our proton patients with an attached electronic device to her during the proton beam, received direct benefit from patient-specific neutron shieling in proton treatment room. Proton patient was receiving chemotherapy that required her to wear infusion pump electronic device at all times during radiation treatment. The patient was treated to pelvis and the pump was placed on her chest during the daily treatment, approximately 30cm from field edge. We studied the estimated out-of-field dose; mSv per Rx Dose, per AAPM TG158, at distance and calculated the required shielding. We used boron poly shielding materials, and had them cut to Lego shaped pieces. The electronic device was placed in a cage-shaped box tightly covering all surrounding the device. After each subsequent fraction, the electronic device was found ON when it was placed inside the shielding box designed and engineered specifically for the patient. The same device was found turned off after fractions when the device was not inside the shielding box. We conclude that, while it is a subtle subject of research and study to investigate the biological effect of proton generated neutrons, importantly it is critical to acknowledge the effect of such neutrons on electronic device attached to proton patients, and be prepared to manage the cases for intermittence and permanent neutron effects on device functionalities.
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WAM-A.8
11:00 The UF-MSK Computational Phantom Library of Adult and Pediatric Patients for Medical Dosimetry RJ Dawson*, University of Florida
; JM Baggett, University of Florida; Y Wang, University of Florida; WW Smither, University of Florida; LE Dinwiddie, University of Florida; SK Wehmeier, University of Florida; SJ Domal, University of Florida; CB Kofler, University of Florida; WE Bolch, University of Florida
Abstract: The ICRP recently published new state-of-the-art mesh-type reference computational phantoms (MRCPs) for use in radiation dosimetry studies. Using these reference phantoms as a starting point, large adult and pediatric (0–15 years of age) phantom libraries have been constructed with heights, weights, and secondary anthropometric parameters representative of the United States population. Body morphometry targets were derived from data published by the Centers for Disease Control and Prevention (CDC). The pediatric library also includes a novel set of newborn-infant-toddler (NIT) phantoms representative of the first two years of life. The phantoms were created using a combination of in-house Python scripting and manual adjustment of the reference models’ subcutaneous fat layer. Low bodyweight phantoms also underwent uniform two-dimensional scaling (with Gaussian falloff at the peripheries) of abdominal organs to prevent collision with the subcutaneous fat mesh. To accommodate larger abdomen and thigh circumferences, a rigging procedure was developed to smoothly deform the limbs while maintaining anatomical realism and preserving tissue masses. This procedure is currently being applied to generate duplicate/sister versions of the libraries with phantoms in an “arms up” position appropriate for computed tomography (CT) dosimetry simulations. Preliminary CT dosimetry with these libraries will be performed using a sparse sampling of phantoms with diverse heights and weights. Organ doses will then be tabulated into pre-computed dose libraries suitable for integration into an Excel-based community software known as MIRDct, which is currently under development and planned for deployment in fall 2022. MIRDct is part of a larger radiation dosimetry platform MIRDsoft that is being developed in partnership between the University of Florida and the Memorial Sloan Kettering Cancer Center.
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