Search

Previously, we have developed DynamicMC for modeling relative movement of Oak Ridge National Laboratory phantom in a radiation field for the Monte Carlo N-Particle package (Health Physics. 2023,124(4):301–309). Using this software, three-dimensional dose distributions in a phantom irradiated by a certain mono-energetic (Mono E) source can be deduced through its graphical user interface. In this study, we extended DynamicMC to be used in combination with the Particle and Heavy Ion Transport code System (PHITS) by providing it with a higher flexibility for dynamic movement for an anthropomorphic phantom. For this purpose, we implemented four new functions into the software, which are (1) to generate not only Mono E sources but also those having an energy spectrum of an arbitrary radioisotope (2) to calculate the absorbed doses for several radiologically important organs (3) to automatically average the calculated absorbed doses along the path of the phantom and (4) to generate user-defined slab shielding materials. The first and third items utilize the PHITS-specific modalities named radioisotope-source and sumtally functions, respectively. The computational cost and complexity can be dramatically reduced with these features. We anticipate that the present work and the developed open-source tools will be in the interest of nuclear radiation physics community for research and teaching purposes. [ABSTRACT FROM AUTHOR]

The core--cladding boundary in step-index plastic optical fibers is imperfect. Surface irregularities locked in during the manufacturing process couple the guided modes by reflecting them in directions that deviate unpredictably from the expected directions. This causes an additional loss as the multiple reflections from surface elements with directions randomized around the nominal for the cylinder transfer the power to the radiation modes that are carried away from the core into the cladding. We model such loss and mode coupling by ray tracing. The irregular core--cladding interface is represented by nominally cylindrical surface elements with orientations randomly perturbed around two geometric axes. The results show mode coupling and relative loss per unit fiber length caused by the core--cladding interface irregularities. The loss is high close to the input fiber end where mode coupling is intense. It drops farther along the fiber as mode coupling slows down and stabilizes where the equilibrium mode distribution is reached. OCIS codes: 060.2310, 080.2730, 060.2270.

Purpose: Neuroendocrine tumors (NETs) are now routinely treated by radiopeptide targeted therapy using somatostatin receptor‐binding peptides such as 90Y‐ and 177Lu‐DOTATOC. The objective of this work was to develop a biokinetics model of 90Y labelled DOTATOC, which is applied in the therapy of NETs to estimate doses in kidney and tumor. Methods: A multi‐compartment model described by two sets of differential equations, one set for the actual 30‐min infusion and the other set for the post‐infusion period was developed and activities were measured by liquid scintillation counting in blood (compartment 1) and the urine (compartment 3). The inter‐compartment transfer coefficients, λij, were varied to yield the best fit of the calculated to the measured time‐activity data and the 90Y‐DOTATOC time‐activity data in the five‐compartments comprising the human body were thus determined. The resulting time‐activity curves were integrated over the interval from 0 to 72 h post administration to obtain the number of radioactive decays in each compartment and, in case of the kidneys and tumor, then multiplied by the self‐dose 90Y beta particle absorbed fraction, determined by Monte Carlo (MC) simulation, the kidney and tumor absorbed doses. Results: Transfer coefficients λij, were determined for five‐compartments for all patients. Time‐ activity curves of 90Y‐DOTATOC in 14 patients were determined, and two typical ones are shown graphically. Absorbed doses in the tumor and kidneys, obtained by the developed method, were determined. The mean absorbed dose in a kidney per unit of administered activity is 1.43 mGy/MBq (range 0.73–2.42 mGy/MBq). The tumor dose was determined as 30.94 mGy/MBq (range 20.05–42.31 mGy/MBq). Conclusion: Analytical solution of a biokinetic model for 90Y‐DOTATOC therapy enabled determination of the transfer coefficients and derivation of time‐activity curves and kidney and tumor absorbed doses for 14 treated patients. The model can be applied to other radionuclides where elimination is predominantly through urine, which is often the case in radiopharmaceuticals. [ABSTRACT FROM AUTHOR]

In response to the comments made by Djordjevich on our previous paper [Appl. Opt. 45, 6675-6681 (2006)], the following clarifications are made. OCIS codes: 060.2310, 060.2400.