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Session: Radiopharmaceutical Therapy Dosimetry [Return to Session]

Computational Benchmarking of Nanoscale Dosimetry in DNA Damaged by 125I Decay

O Kwon*, B Bednarz, University of Wisconsin-Madison, Madison, WI


SU-E-202-8 (Sunday, 7/10/2022) 1:00 PM - 2:00 PM [Eastern Time (GMT-4)]

Room 202

Purpose: Radiopharmaceutical therapy (RPT) is gaining traction as a compelling treatment option for a variety of metastatic cancers. In RPT, the radiation is delivered systemically in the patient to specifically target and kill tumor cells or multicellular clusters. In this respect, the understanding of the effect at the microscopic scale in disease or normal tissue is highly desirable. In this work, a Monte Carlo DNA target model was benchmarked to previously calculated data by comparing the mean energy deposition per decay (E_bar) in short DNA strands for the Auger electron-emitting radionuclide 125I.

Methods: The Geant4-DNA toolkit was benchmarked to a previously simulated DNA damage model. The 82 nucleotides of a double helix B-DNA geometry were implemented using PyMOL and the Protein Data Bank platform. The B-DNA was enveloped in 2.4 nm-diameter and 14.3 nm-height of virtual cylinder structure as the region of scoring. The 125I radionuclide was attached at 41st base position to estimate the distribution of E_bar in base and sugar/phosphate group on the labeled strand. Three Geant4-DNA physics models (options 2, 4, and 6) were used to evaluate E_bar.

Results: The comparison of E_bar at 125I source on base and sugar/phosphate group against MOCA8 were shown various results for options 2, 4, and 6. The most matched results were option 4 with 5.86% and 0.34% differences in base and sugar/phosphate groups. However, the discrepancy was shown at 10th base-pair for both groups from all options, it is likely caused by different physics models and cross-sections between Geant4-DNA (liquid water) and MOCA8 (water vapor).

Conclusion: This work demonstrated good agreement between Geant4-DNA and MOCA8, with differences likely due to different physics models being used in each Monte Carlo code. The results presented here serve as a foundation for future nanoscopic modeling of direct and indirect DNA damage from radiopharmaceuticals.

Funding Support, Disclosures, and Conflict of Interest: NIH National Cancer Institute (NCI), grant P01CA250972.


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