Roger I. Price

A 3D-printed metal solid target using additive manufacturing process is a cost-effective production solution to complex and intricate target design. The initial proof-of-concept prototype solid target holder was 3D-printed in cast alloy, Al–7Si–0.6Mg (A357). However, given the relatively low thermal conductivity for A357 (κ_max, 160 W/m·K), replication of the solid target holder in sterling silver (SS925) with higher thermal conductivity (κ_max, 361 W/m·K) was investigated. The SS925 target holder enhances the cooling efficiency of the target design, thus achieving higher target current during irradiation. A validation production of ⁶⁴Cu using the 3D-printed SS925 target holder indicated no loss of enriched ⁶⁴Ni from proton bombardment above 80 µA, at 11.5 MeV.

The development of a new solid target station for a medium energy medical cyclotron for proton bombardment of target material perpendicular to the incident proton beam with greater than 80 µA at 11.5 MeV, with a current density of >200 µA/cm². A thermocouple is imbedded into the target body to provide constant temperature monitoring during an irradiation while preserving the shuttle transfer mechanism for the target material. The new solid target increases the effective beam current on target from 70 % by reducing the beam loss due to divergence along the beam-line.

Areal bone mineral density (aBMD), derived from dual-energy X-ray absorptiometry (DXA) scanners is used routinely to infer bone strength. With DXA hip scans there is growing acceptance of the advantages of also measuring bone structural geometric variables, that complement conventional aBMD to improve understanding of bone modelling, remodelling and processes of metabolic bone disease. However, phantoms for assessing structural geometric variables from DXA scans are not widely available, unlike those for aBMD. This study describes the development of such a phantom, simulating the cortical shell of the human femoral neck, using dental plaster as a material radiologically similar to cortical bone. The mass attenuation coefficient of the dental plaster differed by < 1% from cortical bone, over the relevant energy range. Performance testing was carried out with DXA, to determine accuracy and precision of the phantom structural geometry, using its dimensions and composition as ‘gold standards’. Accuracy and precision of cortical structural geometry were poor when measured in a simulated 1mm-thick osteoporotic cortex (5.5% precision and 50% accuracy errors), but improved with increasing cortical thickness. This study demonstrates the limitations of DXA-based Hip Structure Analysis when applied to femora with thin cortices, and indicates improvements in the design of a phantom to better simulate such cortical structures.