Improved Accuracy of S-Value Based Dosimetry: Transitioning from Cristy-Eckerman to ICRP Adult Phantoms

BackgroundIn 2016, the International Commission on Radiological Protection and Measurements (ICRP), published the results of Monte Carlo simulations performed using updated and anatomically realistic voxelized phantoms. The resulting absorbed fractions are substantially more accurate than calculations based on the Cristy-Eckerman (CE) stylized (or mathematical) phantoms. Despite this development, the ICRP absorbed fractions have not been widely adopted for radiopharmaceutical dosimetry. To help make the transition, we have established a correspondence between tissues defined in the CE phantom and those defined in the ICRP phantoms. Using pre-clinical data from biodistribution studies performed, we have calculated absorbed doses for Th-227 labeled HER2 targeted antibody. We compare the CE phantom-based calculations as implemented in the OLINDA v1 software with those obtained using ICRP absorbed fractions as implemented in 3D-RD-S, a newly developed software package that implements the MIRD S-value methodology. We also compare ICRP values with a hybrid set of calculations in which alpha-particle energy was assumed completely absorbed in activity containing tissues. ResultsWe observed a non-negligible difference in the absorbed dose calculated using each of the methods for each radiation type. This can be attributed to a combination of greater accuracy in absorbed fraction calculations and differences in the time integrated activity coefficient values due to difference in representation of anatomy by the phantoms. The total absorbed dose for Thorium-227 was dominated by alpha particles, hence the differences in beta and photon absorbed doses were inconsequential in terms of total dose. ConclusionThe results obtained by comparing these different implementations of the MIRD S value methodology provide the data needed to help the field transition to the more anatomically accurate ICRP phantom-based dosimetry. Key words : ICRP phantom, radiopharmaceutical dosimetry, Cristy-Eckerman phantom

Determination of CR-39 and LR-115 Type II Mean Critical Angle of Etching Using a New Monte Carlo Code

CR-39 and LR-115 type II solid state nuclear track detectors (SSNTDs) are both used, in order to assess the concentration of nucleus belonging to 238U and 232Th series, these ones can be also used to measure radon 222Rn and thoron 220Rn gases in different locations. In this paper, a Monte Carlo code was developed to calculate the mean critical angle for which alpha particles emitted from 238U and 232Th families in studied material samples reach CR-39 and LR-115 type II surfaces and bring about latent tracks on them. The dependence of the SSNTDs mean critical angle on the removed thickness, the initial alpha particle energy has been studied. A linear relationship between CR-39 mean critical angle and the initial alpha particle energy for different removed thicknesses has been found. This straightforward relationship allows determining quickly the mean critical angle of etching which corresponds to initial alpha particle energy for a given removed thickness. CR-39 mean critical angle ranged from 59° for an alpha particle emitted by 212Po to 71° for an alpha particle emitted by 232Th, for the value of removed thickness of 6 µm; whereas LR-115 type II mean critical angle does not depend on the initial alpha particle energy except for 232Th, 238U, 230Th and 234Ra when the removed thickness ranged from 6 µm to 8 µm. Obtained data by using the current method and those obtained in the literature [18] are in good agreement with each other.

Validation of the ImageJ package for alpha track counting on Solid State Nuclear Track Detectors

In the present work, an alpha spectroscopic method using CR39 nuclear track detectors is being evaluated, elaborating on track parameters from different alpha particle sources. The freely-available, Java-based ImageJ software was used to obtain the major and minor axis length, the area and the mean gray level of the recorded tracks. A multi-paramater approach based on Principal Component Analysis of the data was subsequently applied and succeeded in grouping the recorded tracks according to alpha-particle energy. The methodology was further applied for the separation of radon progeny on CR39 detectors exposed in a radon chamber.