Browsing by Author "Peca, Stefano"

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    Development and Clinical Application of a New Two-Dimensional in vivo Dosimetry by Electronic Portal Imaging
    (2017) Peca, Stefano; Smith, Wendy; Brown, Derek; Ansbacher, Will; Hahn, Leszek; Kurien, Elizabeth; Ploquin, Nicolas
    In vivo dosimetry (IVD) in radiotherapy refers to direct measurement of dose deposited in the patient during treatment. IVD can be of great use in early detection of harmful errors, for assessment of patient setup and anatomy changes, and to guide adaptive radiotherapy. Routine IVD is hindered by the costs and complexities associated with most systems, and thus has not obtained widespread application. In this thesis I describe a novel method of using the electronic portal imaging device (EPID) for IVD. Images are measured through phantoms/patients making use of treatment beams. From these, 2D dose maps at isocentre depth are calculated from signal-to-dose correlation ratios. Convolution by optimized multi-Gaussian kernels, specific to direction (cross-plane, in-plane), field size, and attenuator thickness, allows dose modelling in the whole plane. The EPID-calculated dose map is compared to that predicted by the treatment planning system (TPS) by pixel-wise comparison, gamma analysis, and a novel approach of morphological connected component analysis. Tests with off-reference values of phantom thickness, field size, and monitor units showed good agreement, with the great majority of points within ±3% of TPS dose. The method was evaluated on 20 patients, spanning multiple body sites and treatment techniques (334 fields). Excluding lung treatments, the mean dose difference at isocentre had good accuracy at 1.5±6.6 %. The large standard deviation is due to both algorithm limitations and true differences, mainly anatomical changes and setup variability. In the isocentre plane, the median area that passed 10% / 3 mm gamma analysis was 96.1%. In three of ten rectal cancer patients, soft tissue differences resulting from suboptimal setup and immobilization devices caused up to 2% overdose to the small bowel. Results suggest that connected component analysis may be as good or superior to gamma analysis for detection of specific dose differences. Further work is necessary before clinical implementation, but EPID IVD by correlation ratios has enormous potential for error detection, process quality assurance, and adaptive treatment guidance, thus increasing safety and quality of radiotherapy.
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    Effects of aging on the association between cerebrovascular responses to visual stimulation, hypercapnia and arterial stiffness
    (Frontiers, 2014-02-19) Fluck, Daniela; Beaudin, Andrew E.; Steinback, Craig D.; Kumparpillai, Gopukumar; Shobha, Nandavar; McCreary, Cheryl R.; Peca, Stefano; Smith, Eric E.; Poulin, Marc J.