Browsing by Author "Hikmettin, Demir"

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Dosimetric Comparison of the Effects of Different Treatment Plan Techniques on Reduction in Critical Organs in Whole Brain Radiotherapy Application
(2024) Hikmettin, Demir; Kanyilmaz, Gul
Different radiotherapy treatment techniques can be used in whole-brain radiotherapy (WBRT). This study aims to investigate the dosimetric advantages of the anterior isocenteric (AI) technique which is produced as an alternative to the central isocentric (CI) technique. 25 whole brain patients were included in this retrospective study. Plans were made with two treatment techniques for each patient. One central isocenter (CI) was made using a conventional helmet field (HF) to center the whole brain, which is the isocenter of the target volume. An automatic margin of 5 mm was given to the planning target volume (PTV) with multileaf collimators (MLC) for both plans. For CI and AI techniques, a total dose of 30 Gy was given in 10 fractions with 6 MV photon energy. The two planning techniques were compared dosimetrically. The dose homogeneity index (DHI) had lower values in the AI plan according to CI plans significantly (p=0.049). There was a 6,57% difference between CI and AI planning techniques for the maximum dose of the right lens. For the minimum dose and mean dose AI plans significantly had lower values according to the CI plan (p=0.001 and p=0.028 respectively). In this dosimetric study, we found that the AI treatment technique for WBRT was superior to the CI technique for DHI and organs at risk. We recommended to use the AI technique, especially to better protect organs at risk in WBRT.
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.