Introduction: In the era of dose escalation for localised prostate cancer, the dose-volume histogram (DVH) is integral to the assessment of rectum and bladder dose constraints. However, reliance on a single planning computerised tomography-based (P-CT) dose distribution may not account for variations in delivered dose that results from deformation of the prostate, bladder and rectum. This study uses conebeam CT (CBCT) datasets from five patients to investigate the concordance between the dose prediction from the initial treatment plan and the dose delivered during treatment.Methods: The intensity-modulated radiation therapy distribution used for treatment was superimposed on alternate day CBCT images for each patient. Dose metrics and absolute volumes for the prostate, rectum and bladder were extracted from the CBCT-based DVH. Differences in dose and volumes were compared with the P-CT values, and significance was tested using the Wilcoxon signed-rank test.Results: For all five case studies, the prostate dose coverage on CBCT plans was lower than predicted with an average reduction of 3% in mean dose. Significant differences in rectal volumes and dose were observed in two out of five and four out of five patients, respectively. Reductions in bladder volume and subsequent increases in dose were observed for three out of five patients.
Conclusion:The DVH from P-CT was unable to consistently predict the dose delivered to the bladder and rectum. The current bowel and bladder preparation protocols used at our institution did not eliminate variation in bladder and rectum volumes for the five patients included in this study.
Optical waveguides have been formed by helium-ion implantation in KTaO3. The implantation forms a confinement barrier near the projected range of the ion by decreasing the refractive index as much as 16% for ion doses of 4×1016 ions/cm2. This is the highest refractive-index change yet reported for ion-implanted crystalline planar waveguides. Guiding modes (with moderately low loss) are produced without the need for annealing out of color centers. During annealing studies, the index change reduces during an anneal stage near 400 °C, but waveguiding is maintained even after anneals to 900 °C. Loss measurements indicate a planar-waveguide loss of <1 dB/cm after a 400 °C anneal.
XEI Scientific Inc. is a recognized manufacturer of plasma cleaners that have been proven to be very effective in removing adventitious hydrocarbon contamination from electron microscope chambers [1]. Over 15 years there are no reports of X-ray window failure or damage to EDS detectors on SEM chambers due to oxygen radicals generated by the Evactron plasma cleaners.
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