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Reatment field to ensure that the entire tumor was included within the portal. However, the larger fields would also irradiate more healthy tissues and could lead to an increase in side effects. The increase in side effects could limit the radiation oncologist's ability to deliver a dose large enough to destroy a tumor. Conversely, if the oncologist reduced the field margin in order to limit side effects the chance of missing part of the tumor could also limit the chance of cure. viagra online It would take the development of the ct scanner to address this problem. The invention of the ct scanner was one of the most important developments in x-ray imaging. In radiation therapy, beginning in the 1980s, the ct scanner had a dramatic impact on the planning of radiation fields. Ct images have far better soft tissue contrast than plain films and allow the oncologist to view the tumor from an axial or crosscut view. buy viagra This made it much easier for the radiation oncologist to identify the full extent of a tumor and allowed for a potential reduction in the volume of normal tissue irradiated. where can i buy viagra online yahoo answers This would give the oncologist more confidence to treat tumors to higher doses safely. viagra in canada Ct based planning is still the standard of practice today. Although ct based planning has resulted in more accurate targeting of tumors the ability to further reduce field margins is limited due to tumor motion. generic viagra online It has been shown with a number of studies that tumors move during the course of therapy due to a number of factors including breathing, swallowing and bladder filling. This has resulted in a limit to which field sizes can be reduced because of the need to cover the tumor and its motion. Because of this motion it has become necessary in some cancers to localize or precisely identify the location of a tumor relative to healthy tissues on a daily basis. The technology and processes that allows for daily tumor localization has come to be know as igrt. does viagra work on women too Many different technologies have been developed to aid in the daily localization of tumors. viagra generic These technologies include ultrasound imaging, daily ct imaging and implantable fiducials or markers. At the c. R. Wood cancer center we have recently adopted the implantable marker technology to treat prostate cancer. The markers are very small gold seeds that are 3 mm long and 1 mm in diameter. Gold is used because it is radio-opaque or easily seen with x-rays. The markers are crosscut to prevent the seeds from moving once they are implanted. The seeds are implanted in the urologist office. cheap viagra online The procedure takes about a half-hour. Under ultrasound guidance the urologist will place three seeds into the prostate gland. buy cheap viagra The placement of the seeds i.