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Simplification of Transmission Factor Determination for I-131 Gamma Camera Based Internal Dosimetry with Co-57 Solid Flood Source

Q Liang1*, L Chen2, R Klein3, J Halama4, R Harvey5, J Schwartz6, D Fisher7, (1) Actinium Pharmaceuticals, New York, NY, (2) Banner MD Anderson Cancer Center, Gilbert, AZ, (3) The Ottawa Hospital, Ottawa, ON, Canada, (4) Loyola Univ Medical Center, Maywood, IL, (5) Roswell Park Cancer Institute, Buffalo, NY, (6) Memorial Sloan Kettering Cancer Center, New York, NY, (7) Versant Medical Physics And Radiation Safety, Richland, WA


(Sunday, 7/12/2020)   [Eastern Time (GMT-4)]

Room: AAPM ePoster Library

Purpose: common approach to obtain transmission correction for planar imaging-based dosimetry with MIRD schema is to measure the transmission factor with a flood source of the same isotope of interest (I-131). However, preparing a liquid I-131 filled flood source presents operational challenges. The feasibility of obtaining transmission factors with a Co-57 solid flood source, which is widely available and easily handled, was investigated as a sub-study of a phase III clinical trial for a novel I-131 labeled antibody (I-131 Apamistamab, Iomab-B) conditioning agent for relapsed and refractory acute myeloid leukemia prior to bone marrow transplant.

Methods: factors (?) were obtained from the anterior images of an I-131 and a Co-57 flood source with and without the positioning patients for both the abdomen and pelvis regions. The ratio of ?I-131 to ?Co-57 is defined as Transmission Ratio (TR). A phantom study was performed following the same procedure using tissue-equivalent phantoms with different thicknesses (12-34 cm, 2 cm increments) to demonstrate the relationship between TR and thickness (t). Results for 11 patients were summarized and the TR vs.t relationship was established as a look-up curve. Dose calculations for three organs (liver, spleen, marrow) were performed retrospectively with TR corrected ?Co-57. The results were compared with dosimetry calculated with ?I-131.

Results: the phantom study data fitted with an exponential and a line showed equivalent goodness-of-fit, a linear relationship was used to represent the relationship between TR and t. Liver, spleen and marrow dose calculated with ?Co-57 show median differences from dose calculated with ?I-131 by 1.5% [-4.3, 5.8%], 1.8% [-5.1, 5.7%], and -2.5% [-8.7, 5.2%].

Conclusion: calculations with Co-57 measured transmission factors for I-131 labeled antibody dosimetry show the feasibility to replace I-131 flood source with Co-57 solid flood source. This could simplify the performance of planar dosimetry scans in clinic.

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Funding Support, Disclosures, and Conflict of Interest: Qing Liang is an employee of Actinium Pharmaceuticals.


Quantitative Imaging, MIRD, Transmission Measurements


IM/TH- Image Analysis (Single Modality or Multi-Modality): Quantitative imaging

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