| Abstract [eng] |
mages in computed tomography are generated by using rotatory gantry and detector array movement around the patient. This fundimentally poses a problem whenever the scanned projection intercepts a dense object or a patient implant in its path. Due to the density of these implants, x-rays scattering effects may occur, creating shadow-stripe type artifacts. In many cases of radiotherapy, these artifacts are either overlooked or ignored. Only rarely they are reduced using the commercial metal artifact reduction algorithms. The re-distribution of the doses when comparing original CT images to MAR reduced images can be significant enough to sometimes reduce unwanted potential after-treatment radiation induced side effects The aim of this paper was to evaluate the difference and re-distribution of doses to the target organs of the patients, as well as organs at risk surrounding them, according to the organ dose constraint guidelines. A metallic artifact reduction (MAR) algorithm was constructed, using different types of filtering methods traditionally used in photography and other image editing fields, for edge (detail) enhancement as well as overall image noise and blur reduction. CT data sets of 7 patients in total were evaluated for potential edge drifting and dose reduction in radiotherapy planning system. For further data evaluation, patients were split in to two groups. One group consisted of 4 patients of prostate cancer patients, while the other group consisted of 3 patients of cervix-uterus cancer patients. It was found that the application of the MAR algorithm has resulted in a high dose reduction to the organs of interest. On average a 14.03% dose reduction to the target organ was determined for the cervix-uterus cancer patients as compared to the 2.26% dose reduction of the prostate cancer group. Dose reduction for organs at risk has also been significantly higher in the cervix-uterus cancer group of patients. Rectum organ dose on average was reduced by 8.59% among all patients of the second group, while dose reduction to the rectum in the first group was 2.26% only. Bladder in the second group of patients received a 8.53% dose reduction, contrary to the increased average dose of 4.45% for the first group of patients. It was shown that, the application of metal artifact reduction algorithm before radiotherapy treatment planning, which is based on the patients CT images, is of high importance, since these algorithms provide a significant reduction of dose to all organs surrounding target and substantial dose re-distribution. Images in computed tomography are generated by using rotatory gantry and detector array movement around the patient. This fundamentally poses a problem whenever the scanned projection intercepts a dense object or a patient implant in its path. |
