Traditionally, beam angle selection for intensity‐modulated radiation therapy (IMRT) plans has been left up to the experienced dosimetrist. However, the large number of potential angle orientations suggests that the human plan may not be ideal. A learning algorithm (a variation of a genetic algorithm) was written to select beam angles to produce plans with more desirable dose‐volume histograms (DVH). The algorithm is used in parallel with the commercial Pinnacle3 Radiation Therapy Planning System. Starting with a generation of randomly chosen beam angles, the algorithm uses Pinnacle's built‐in hot scripting to call on the P3 IMRT portion of the software to perform dose calculations on each individual. Each set of angles is then ranked using a dosimetric fitness function that uses the same constraints that are used during the IMRT calculations. A new generation of beam angles is then constructed using both biologically and non‐biologically relevant operators. Operator weights are also adjusted each generation based on the dosimetric fitness function as well. Once completed, the algorithm was tested on several IMRT prostate cases. In each case, the DVH for the algorithm‐selected plan fit the dose constraints better than the human‐designed IMRT plan. A major drawback was the long running time of the algorithm (up to 11 hours), which was constrained almost entirely by the speed of Pinnacle's IMRT calculations. The ideal use of the code would be for overnight applications, with the human planner then using the optimized beam angles to plan as normal. This research was supported by the Graduate Internship program of the MITACS Network of Centres of Excellence and the Local Investigator Research Fund of the Windsor Regional Cancer Centre.
Radiation therapy has been used in the treatment of a wide variety of cancers for nearly a century and is one of the most effective ways to treat cancer. Low-dose ionizing radiation (IR) can interfere with cell division of cancer and normal cells by introducing oxidative stress and injury to DNA. The differences in the response to IR-induced DNA damage and increased reactive oxygen species between normal human fibroblasts (NHFs) and cancerous SHSY-5Y cells were considered. H2AX staining and comet assays revealed that NHF cells responded by initiating a DNA repair sequence whereas SHSY-5Y cells did not. In addition, NHF cells appeared to quench the oxidative stress induced by IR, and after 24 h no DNA damage was present. SHSY-5Y cells, however, did not repair their DNA, did not quench the oxidative stress, and showed characteristic signs that they were beginning to undergo apoptosis. These results indicate that there is a differential response between this cancerous and normal cell line in their ability to respond to low-dose IR, and these differences need to be exploited in order to treat cancer effectively. Further study is needed in order to elucidate the mechanism by which SHSY-5Y cells undergo apoptosis following radiation and why these normal cells are better equipped to deal with IR-induced double-strand breaks and oxidative stress.
Purpose: In Ontario, shielding for all X‐ray machines, including CT scanners, must be evaluated according to Safety Code 20A (Health Canada, 1983) which is based on NCRP‐49 (NCRP, 1976). NCRP‐147 (NCRP, 2004) is the international standard for shielding calculations of CT scanners and is also referenced in Safety Code 35 (Health Canada, 2008) which, was published to supersede SC20A. The goal of this work is to demonstrate the cost effectiveness of NCRP‐147 for CT scanner shielding. Methods: CT scanner shielding calculations are performed using SC20A and NCRP‐147: A room located on the third floor with the nearest building 75m away A room with high occupancy uncontrolled adjacent spaces Two side by side rooms on the main floor Results: 1. SC20A: The exterior windows required 0.1mm of Pb to protect the public who may occupy the building at 75m. 1. NCRP‐147: No additional shielding required. 2. SC20A: Two walls adjacent to high occupancy uncontrolled space required an additional 1.58mm Pb. 2. NCRP‐147: No additional shielding required. 3. SC20A: The entire floor and ceiling slabs in both rooms required an additional 0.79mm Pb. In addition, 0.79mm Pb was added to the walls from the ceiling to overlap the existing Pb shielding in the walls. 3. NCRP‐147: No additional shielding required. Conclusion: The application of NCRP Report No. 147 affords the required protection to staff and the public, in the true spirit of the ALARA principle, taking into account relevant social and economic factors.
This poster will be strictly based on the Healing Arts Radiation Protection (HARP) Act, Regulation 543 under this Act (X‐ray Safety Code), and personal communication the presenting author has had. In Ontario, the process of approval of an X‐ray machine installation by the Director of the X‐ray Inspection Service (XRIS) follows a certain protocol. Initially, the applicant submits a series of forms, including recommended shielding amounts, in order to satisfy the law. This documentation is then transferred to a third‐party vendor (i.e. a professional engineer – P. Eng.) outsourced by the Ministry of Health and Long‐term Care (MOHLTC). The P.Eng. then evaluates the submitted documentation for appropriate fulfillment of the HARP Act and Reg. 543 requirements. If the P.Eng.'s evaluation of the documentation is to their satisfaction, the XRIS is then notified. Finally, the Director will then issue a letter of approval to install the equipment at the facility. The methodology required to be used by the P.Eng. in order to determine the required amounts of protective barriers, and recommended to be used by the applicant, is contained within Safety Code 20A. However, Safety Code 35 has replaced the obsolete Safety Code 20A document and employs best practices in shielding design. This talk will focus further on specific intentions and limitations of Safety Code 20A. Furthermore, this talk will discuss the definition of the “practice of professional engineering” in Ontario. COMP members who are involved in shielding design are strongly encouraged to attend.
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