HPS 66th Annual Meeting

Phoenix, Arizona
July 25th-29th 2021

Single Session

[Schedule Grid]

THAM-B - Medical

North 222ABC   08:00 - 10:15

THAM-B.1   08:00  Brachytherapy For Brain Metastases: Radiation Safety Considerations For Cs-131 GammaTile K Prasad*, Memorial Sloan Kettering Cancer Center ; NS Moss, Memorial Sloan Kettering Cancer Center; D Aramburu-Nunez, Memorial Sloan Kettering Cancer Center; BP Chu, Memorial Sloan Kettering Cancer Center; LT Dauer, Memorial Sloan Kettering Cancer Center

Abstract: Brachytherapy for the brain was first performed in 1936 using radon seeds and has since evolved to several different radioisotopes including I-125 and Cs-131. Approved by the FDA in 2003, Cs-131 offers several clinical and radiation protection advantages over I-125 and Pd-103 implants. At our institution, intraoperative radiation therapy for recurrent brain metastases has been performed in 20 patients, with 24 resected tumor beds. Exposure to intraoperative staff, specifically the Neurosurgeon and Radiation Oncologist, was monitored with NVLAP accredited extremity ring dosimeters. For patient release considerations, NCRP and ICRU guidelines were used to develop an algorithm for modeling lifetime exposure to family and ancillary staff caring for the patient based on measured dose rates. Median number of seeds implanted were 16 (range 6-46) of 3.50 U seed strength (3.27-3.81), resulting in dose rates of 1.19 mSv/hr on contact (0.28 – 3.3), 0.08 mSv/hr (0.01 – 0.35) at 30 cm, and 0.01 mSv/hr (0.001 – 0.03) at 100 cm from the patient. Median intraoperative ring dosimeter exposures were 0.04 mSv for the Radiation Oncologist and 0.09 mSv for the Neurosurgeon. Average modeled lifetime exposure to family was 0.86 mSv and 0.06 mSv to patient facing staff accounting for self-shielding via skull and soft tissue attenuation. Precautions for caregivers were grouped into brackets based on real-time dose rate measurements ranging from 1-3 weeks for adults, and longer for pregnant women and children, with recommendations to avoid prolonged close contact. Additional evaluations were conducted for 2 patients with multiple brachytherapy placements. The algorithm designed provides evidence-based, safe and compliant recommendations for the use of Cs-131 Central Nervous System Brachytherapy with the flexibility for programmatic development and growth.

THAM-B.2   08:15  Managing Third Party Lasers in a Healthcare System DH Elder*, UCHealth

Abstract: The use of lasers that are rented or provided for demonstration can save facilities money and allow physicians to trial a new laser before purchase. It is often assumed that the facility has very little responsibility related to the use of these lasers because a laser operator is provided and the vendor maintains and calibrates the equipment. However, the 2018 version of the American National Standard for Safe Use of Lasers in Health Care has specified additional facility responsibilities. The health care facility shall ensure that the credentials of the laser operators and the documentation meet the facility policy. The facility must also receive documentation to confirm that the laser maintenance and service are up-to-date and there should be an intake procedure that includes, but is not limited to, assessment of the condition of the laser system and credentials of the technician. Working with the clinical engineering and surgery departments, new procedures were developed to comply with the revised standards. Having a streamlined process that would work for the facility clinical engineering staff and the vendor representatives was a priority, so a pre-authorization program was implemented.

THAM-B.3   08:30  Estimated Dose Rates to Members of the Public from External Exposure to Pediatric Patients Receiving 131I Thyroid Treatment LC Aziz*, Texas A&M University ; SA Dewji, Texas A&M University

Abstract: Radioactive iodine (RAI) therapy using 131I can be used to treat patients with thyroid dysfunction such as hyperthyroidism and differentiated thyroid cancer (DTC). In the case of DTC, papillary and follicular account for the majority of tumor subtypes where cells in the thyroid gland, continue to grow irregularly, forming a mass in one or both lobes of the thyroid that appear microscopically similar to normal thyroid tissue. Hyperthyroidism refers to when the thyroid is overstimulated and produces excess thyroxine hormone (T4) that adversely accelerates the body’s metabolism causing many symptoms, including the worsening of a DTC prognosis. While previous work focused on adult patients and adult members of the public with no time dependent considerations, little has been considered in regard to age-specific pediatric cases, both as patients and exposed members of the public. The improvements to public protection and patient release criteria account for age-dependent analysis (both patient and public) are proposed in radiation transport simulations of age-specific phantoms correlated with biokinetics post-administration of RAI therapy to determine a time dependent effective dose. Results demonstrated current patient release regulatory guidelines overestimated dose to patients and members of the public at minimum by a factor of two across age groups, indicating that time-dependent age-specific models more accurately determined the time at which release can occur to is potentially sooner than current tools provided in regulatory guidelines to licensees.

THAM-B.4   08:45  Exposure Rate and Detector Response Data for Operational Monitoring of I-131 Patient Release LC Aziz*, Texas A&M University ; SA Dewji, Texas A&M University

Abstract: The Nuclear Regulatory Commission Regulatory Guidance 8.39 determines patient release criteria for those undergoing radioactive iodine therapy based on over-simplified point source methods. 131I can be used to treat patients with thyroid dysfunction such as hyperthyroidism and differentiated thyroid cancer (DTC). While previous work focused on adult patients and adult members of the public with no time dependent or physical anatomical considerations, little has been evaluated in regard to recommendations on guidance for age-specific pediatric cases, both as patients and exposed members of the public, including correlations with monitoring instrumentation. The proposed improvements to public radiation protection and patient release criteria provide alternative approaches to the licensee than over-simplified point source methods to account for age-dependent analysis (both patient and public) utilizing state of the art Monte Carlo radiation transport simulations of age-specific phantoms correlated with biokinetics post-administration of RAI therapy for exposure rates. Radiation detection models of the Captus 3000 Thyroid Uptake Probe were constructed with which detector responses were calculated as a function of time post-131I administration. Count rates were correlated with exposure rate data from 10-year-old, 15-year-old, and adult patients and compared to the NRC RG. 8.39 point source method. Results demonstrated current patient release regulatory guidelines overestimated exposure at minimum by a factor of 2 across age groups and higher count rates in DTC 10-year-old patients. The time-dependent age-specific models presented provide alternative methods for a licensee to release a patient and can better inform regulatory agencies in future revisions of patient release criteria the time at which release can occur.

THAM-B.5   09:00  Patient release and patient trash; building relationships with sanitation departments MJ Williamson*, Memorial Sloan Kettering Cancer Center ; M Shuksta, The City of New York Department of Sanitation; B Chu, Memorial Sloan Kettering Cancer Center

Abstract: Regulatory pathways controlling byproduct material of patients containing radiopharmaceutical or permanent implants have recognized the need to address how to handle waste from patients. Several regulatory guidance documents and countless literatures provide mechanisms that demonstrate compliance with the United States Nuclear Regulatory Commission (US NRC) rule found in 10 CFR 35.75 which is a dose-based criterion minimizing radiation dose to the public. The recent revision to US NRC Reg Guide 8.39 includes suggested patient precautions to minimize external radiation exposure and potential internal exposure from contaminated objects. The guidance also asks licensees to evaluate the need for instruction on segregation of patient related trash which may alarm radiation detectors at waste disposal facilities that could lead to the items going back to the patient. Segregated trash should be stowed as to further minimize exposure. Our institution (Memorial Sloan Kettering Cancer Center) performed over 1,000 therapeutic procedures using sealed and unsealed sources (§§35.300, 35.400, and 35.1000) in 2019; the great majority of these as outpatient procedures. We wish to share our experiences with waste from patients released in accordance with §35.75. The most impressive includes a new-found relationship with the NYC Department of Sanitation (DSNY). The DSNY, with over 2000 collection trucks in a city with over 8 million people, describes obstacles encountered with containerized waste that alarms radiation detectors. As cancer treatments change using new and/or increased levels of radionuclides, medical facilities adapt with updated equipment and radiation safety instrumentation. Patient instruction also evolves based on identified trends. New York’s Strongest show their resilience during these times.

THAM-B.6   09:15  Design of a Mobile Brachytherapy Unit to Deliver Treatment to Patients in Remote Locations. SA Dewji, Texas A&M University ; A Willis, Texas A&M University; MI Dailey*, Texas A&M University; M Steinohrt, Texas A&M University; S Tezel, Texas A&M University

Abstract: A High Dose Rate (HDR) Remote Afterloader is used to insert a radioactive source, Ir-192, directly into a tumor. This form of cancer treatment, while highly effective is not accessible to individuals living in many rural areas, due to the infrequency of its use and maintenance cost. Ir-192 has a half-life of ~74 days, meaning these sources needed to be changed out every few months in order to maintain their effectiveness as a cancer treatment. Creating a mobile brachytherapy unit would allow hospitals to rent out the service on an as-need basis. Additionally, a mobile brachytherapy unit would allow access to patients who are unable to travel to hospitals with the necessary equipment for medical or personal reasons. Monte Carlo N-Particle (MCNP) radiation transport code will be used to determine the shielding required to make this mobile unit feasible. Based on shielding requirements and regulations, the design and implementation considerations for the mobile HDR brachytherapy unit will be discussed.

THAM-B.7   09:30  Radiation Protection Considerations for High Power Linear Accelerators Used in FLASH Radiotherapy A Rosenstrom*, Texas A&M University ; M Santana, SLAC National Accelerator Laboratory; S Rokni, SLAC National Accelerator Laboratory; S Dewji, Texas A&M University; B Loo, Stanford University

Abstract: A new external beam radiotherapy modality utilizing the so-called "FLASH" effect has been shown to increase the therapeutic index in the treatment of certain cancers compared to conventional radiotherapy treatments. A new preclinical radiotherapy device using high-energy bremsstrahlung photons is being developed at Stanford University in association with SLAC National Accelerator Laboratory. A multilayered shielding methodology is developed in order to effectively shield the high-intensity secondary radiation generated by the machine during subject irradiation. This methodology utilizes alternating photon and neutron shields in order to take advantage of their shielding characteristics and reduce the adverse secondary radiation that is produced and create a compact and portable shielding design. The Monte Carlo radiation transport code FLUKA v2020.0 is utilized in order to simulate the quantities of interest, which are the fluence rate and effective dose rate due to photons and neutrons. The shielding design for high power radiotherapy tools was performed such that it meets the effective dose rate requirements set by the National Council on Radiation Protection and Measurement (NCRP) in Publication 151. Four shielding designs were simulated; the multilayered shielding design produced a shielding design that has a 440% reduction in radiation leakage and a 13% reduction in the shielding mass compared to a traditional shielding design with identical shielding material thicknesses.

THAM-B.8   09:45  Radiation Dosimetry following Inadvertent Extravasation Events in Nuclear Medicine DR Fisher*, Versant Medical Physics and Radiation Safety

Abstract: With the advent of high-dose theranostic agents (for both diagnostic and therapy), particular care must be exercised to ensure that high-activity therapy agents are completely delivered into the artery or vein. Inadvertent injection of a radiopharmaceutical agent into a patient’s arm tissue instead of into the appropriate blood vessel can cause the injection to infiltrate underlying tissue and produce high-dose radiation localized to the patient’s arm and skin tissue. Immediate symptoms of extravasation may include swelling, edema, pain, or numbness in the vicinity of the extravasation site; inflammation; and drainage from the site. Some infiltrations may go unnoticed until later. Another important concern includes failure to deliver a prescribed amount of radiopharmaceutical to the patient for its intended purpose. When this type of misadministration occurs, called an extravasation event, it should be recognized, mitigated, and monitored for patient health and safety. Two target tissues of concern for adverse reactions include (1) the infiltrated dermal and fascia tissues, and (2) the proximate basal cell layer of skin epithelium. Standard MIRD methods may be used to calculate the absorbed dose to infiltrated tissue. This requires a measure of infiltrated tissue activity, geometr,y and volume, as well as the effective clearance rate. In addition, the shallow dose equivalent (Sv) to the sensitive basal cell layer for the highest relevant area of the skin (10 cm2) may be calculated using using VARSKIN6.1. Patient-specific count-rate data, calibration against known activity levels, and dose assessment can help clinicians determine whether an extravasation is severe and whether the patient should be followed for adverse tissue reactions that may present later in time.

[back to schedule]