WE‐C‐108‐10: Model‐Based Dose Calculations for Eye Plaque Brachytherapy

Purpose: To develop a comprehensive understanding of dosimetry for ocular brachytherapy through model‐based dose calculations involving a full human eye model for various plaque models and three different photon‐emitting radionuclides (125I, 103Pd and 131Cs). Methods: A representative computational model of the human eye and surrounding tissues was developed based on ocular geometry and compositions from the literature. Mass energy absorption and attenuation coefficients for all media were calculated. Monte Carlo simulations using the EGSnrc user‐code BrachyDose were performed for a variety of photon‐emitting plaques covering the range of plaque models encountered in clinical practice, including the widely‐used COMS plaque. Maximum, minimum and average doses to ocular structures, as well as dose volume histograms (DVH) for the full eye model were compared to those for a homogeneous water phantom, both including and excluding (TG‐43) inter‐seed and eye plaque effects. Results: Mass energy absorption and attenuation coefficients for ocular media differ from those for water by up to 10% for photon energies in the 10–30 keV range. For the COMS plaque in the full eye model, average doses to important structures such as the tumour and lens differ from those for the plaque in water by roughly 8–10% and 13–14%, respectively, and from TG– 43 calculation by 2–17% and 29–34%, respectively. Maximum, minimum and average doses differ considerably from doses to points of interest (as they are currently reported); the lens has a larger average dose by 7–9% and optic nerve has a larger maximum dose by 16–22%, than at the center of the lens and the optic disk, respectively. Conclusion: Dose distributions for the full eye model simulations deviate significantly from TG‐43 and from simulations that include the plaque but assume the eye to be water equivalent, highlighting the need for accurate model‐based dose calculations in ocular brachytherapy. Funding support: NSERC, OGS

Model-based dose calculations for COMS eye plaque brachytherapy using an anatomically realistic eye phantom

Purpose: To investigate the effects of the composition and geometry of ocular media and tissues surrounding the eye on dose distributions for COMS eye plaque brachytherapy with125I, 103Pd, or 131Cs seeds, and to investigate doses to ocular structures. Methods: An anatomically and compositionally realistic voxelized eye model with a medial tumor is developed based on a literature review. Mass energy absorption and attenuation coefficients for ocular media are calculated. Radiation transport and dose deposition are simulated using the EGSnrc Monte Carlo user-code BrachyDose for a fully loaded COMS eye plaque within a water phantom and our full eye model for the three radionuclides. A TG-43 si

Palaeolithic artefact deposits at Wadi Dabsa, Saudi Arabia; a multi-scalar geoarchaeological approach to building an interpretative framework

Surface artifacts dominate the archaeological record of arid landscapes, particularly the Saharo‐Arabian belt, a pivotal region in dispersals out of Africa. Discarded by hominins, these artifacts are key to understanding past landscape use and dispersals, yet behavioral interpretation of present‐day artifact distributions cannot be carried out without understanding how geomorphological processes have controlled, and continue to control, artifact preservation, exposure and visibility at multiple scales. We employ a geoarchaeological approach to unraveling the formation of a surface assemblage of 2,970 Palaeolithic and later lithic artifacts at Wadi Dabsa, Saudi Arabia, the richest locality recorded to date in the southwestern Red Sea coastal region. Wadi Dabsa basin, within the volcanic Harrat Al Birk, contains extensive tufa deposits formed during wetter conditions. We employ regional landscape mapping and automatic classification of surface conditions using satellite imagery, field observations, local landform mapping, archaeological survey, excavation, and sedimentological analyses to develop a multiscalar model of landscape evolution and geomorphological controls acting on artifact distributions in the basin. The main artifact assemblage is identified as a palimpsest of activity, actively forming on a deflating surface, a model with significant implications for future study and interpretation of this, and other, surface artifact assemblages