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Electron blocks are typically composed of a low melting point alloy (LMPA), which is poured into an insert frame containing a manually placed Styrofoam aperture negative used to define the desired field shape. Current implementations of the block fabrication process involve numerous steps which are subjective and prone to user error. Occasionally, bowing of the sides of the insert frame is observed, resulting in premature frame decommissioning. Recent works have investigated the feasibility of utilising 3D printing technology to replace the conventional electron block fabrication workflow; however, these approaches involved long print times, were not compatible with commonly used cadmium-free LMPAs, and did not address the problem of insert frame bowing. In this work, we sought to develop a new 3D printing technique that would remedy these issues.
Materials and Methods:
Electron cutout negatives and alignment jigs were printed using Acrylonitrile Butadiene Styrene, which does not warp at the high temperatures associated with molten cadmium-free alloys. The accuracy of the field shape produced by electron blocks fabricated using the 3D printed negatives was assessed using Gafchromic film and beam profiler measurements. As a proof-of-concept, electron blocks with off-axis apertures, as well as complex multi-aperture blocks to be used for passive electron beam intensity modulation, were also created.
Film and profiler measurements of field size were in excellent agreement with the values calculated using the Eclipse treatment planning system, showing less than a 1% difference in line profile full-width at half-maximum. The multi-aperture electron blocks produced fields with intensity modulation ≤3.2% of the theoretically predicted value. Use of the 3D printed alignment jig – which has contours designed to match those of the insert frame – was found to reduce the amount of frame bowing by factors of 1.8 and 2.1 in the lateral and superior–inferior directions, respectively.
The 3D printed ABS negatives generated with our technique maintain their spatial accuracy even at the higher temperatures associated with cadmium-free LMPA. The negatives typically take between 1 and 2 hours to print and have a material cost of approximately $2 per patient.
A retrospective, cross-sectional telephone survey (n=2090) was conducted in Ontario, Canada, between May 2005 and April 2006, to determine the burden of acute gastrointestinal illness in the population. The 4-week prevalence was 8·56% (95% CI 7·36–9·76); in households with more than one resident, 35% of cases reported someone else in their household had similar symptoms at the same time. The annual adjusted incidence rate was 1·17 (95% CI 0·99–1·35) episodes per person-year, with higher rates in females, rural residents, and in the winter and spring. Health care was sought by 22% of cases, of which 33% were asked to provide a stool sample. Interestingly, 2·2% of cases who did not visit a health-care provider reported self-administering antibiotics. Overall, acute gastrointestinal illness appears to pose a significant burden in the Ontario population. Further research into the specific aetiologies and risk factors is now needed to better target intervention strategies.
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