Browsing by Author "Gül, Osman Vefa"

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The Effect of Contrast Material in Three Dimensional Conformal and Helical Treatment Plans in Rectal Radiotherapy
(2024) Hikmettin, Demir; Kanyilmaz, Gul; Gül, Osman Vefa
The aim of this study to investigate the impact of contrast agent used for imaging purposes in the treatment of neoadjuvant rectal cancer patients. In rectal radiotherapy, contrast agent is used during the treatment simulation but the patient treated without contrast. In our study, we will examine whether CTs taken with contrast agent are sufficient for clinical application. A total of eighteen patients who had undergone neoadjuvant treatment with rectal cancer randomly selected. Two different CT scans were performed for each patient. The contours were delineated on a non-contrast CT images with the help of image fusion with contrast CT images. Then, the contours drawn on the non-contrast CT were copied to the contrast-enhanced CT with the help of fusion to be used in contrast CT plans for our retrospective study. Subsequently, all plans were generated in Eclipse TPS and Accuray Precision TPS. Finally the plans with contrast agent and non-constrat agent were compared. 3DCRT plans were compared for contrast and non-contrast images, no significant differences were observed in either the PTV or the maximum and mean values of critical organs. It was observed that the average post-contrast doses increased significantly for small bowel only in helical therapy (p = 0.019). As a result, no significant difference was observed in terms of PTV and critical organs in the comparison of 3DCRT plans. In the comparison of helical plans, there was only a significant difference in the bladder. Based on these results, we suggest that planning can be done with a single contrast CT for 3DCRT treatments, both to avoid further discomfort for the patient and to prevent additional tomography doses. On the other hand, for helical therapy, we believe that it can be clinically evaluated whether the treatment will be performed with contrast CT depending on the patient's condition.
Measuring Out-Of Dose to the Whole Brain in Radiotherapy
(Yuzuncu Yil Universitesi Tip Fakultesi, 2024) Gül, Osman Vefa; Tuğrul, Taylan; Hikmettin, Demir
The aim of this study is to measure out-of-field lens and thyroid doses in whole brain radiotherapy with thermoluminescence dosimeters (TLD) and compare them with treatment planning system (TPS) calculation values. Before Computed Tomography (CT), TLDs were placed on the lens and thyroid surfaces of the rando phantom and then the phantom was scanned with CT. Data was transferred from CT to RayStation™ TPSs and then target volume and critical organs were determined. The treatment plan was created. TLDs were placed on the lens es and thyroid for out-of- field dose measurement. For the right lens, the mean value of TLD measurements were 188.3±2.2 cGy and the mean values of TPS measurement were 192.0±0.2 cGy. The average TLD measurement for the left lens was 190.2 ±0.5 cGy, and the average TPS dose reading was 192.0±0.1 cGy. For doses in the thyroid region, which is further from the target, the TLD measurement and TPS reading averages were 44.9±5.2 cGy and 40.9±6.3 cGy, respectively. Accordingly, right lens point doses calculated from TPS were 1.93% higher than TLD measurements. For the left lens, this difference in the same direction was determined as 0.93%. Within the thyroid region, TLD measurements were observed to be higher than TPS readings. We measured out-of-field doses via TLDs and found that TPS calculations for thyroid were 8.90% lower than the measured dose. The results we obtained from our study are guiding in estimating out -of-field lens and thyroid doses in 3DCRT whole brain irradiation.