Browsing by Author "Hikmettin, Demir"

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Comparative Analysis of Percentage Depth Dose Calculations by Radiotherapy Treatment Planning System Algorithms in Non-Homogeneous Media
(Yuzuncu Yil Universitesi Tip Fakultesi, 2025) Çakır, Tahir; Hikmettin, Demir
This study aims to investigate the dose distributions produced by three treatment planning systems (TPSs) across various mediums by constructing a phantom that simulates a mediastinal environment. Materials and Methods: We utilized Computerized Tomography (CT) to scan a phantom with bone, PMMA, and lung blocks. It was subsequently moved to Eclipse™ TPS. In Eclipse TPS, we utilized a 6 MV photon beam with a Source Skin Distance of 100 cm and a field size of 20x20 cm2. We obtained the percentage depth doses (PDD) by recording the dose at 3 mm intervals from the center of each block to the desired depths. These processes were repeated for the other two TPSs. We observed that the PDD acquired from bone, PMMA, and lung blocks in Eclipse TPS using the PBC algorithm revealed a significant contrast in the bone block, which increased a s we move away from the build-up area. Subsequently PDD values from the lung medium are compared. Eclipse and Prowess TPS values were found to be similar, while Monaco TPS, utilizing the Monte Carlo Algorithm, demonstrated significant difference. Although Monaco TPS recorded higher PDD values compared to the other two TPSs both before and after the build -up region, it maintained a consistent level in the build-up region and yielded slightly lower doses than the other TPSs. The behaviors of TPSs employed in commercial radiotherapy planning should be calculated in different environments, and compared with the measured values. These differences should be taken into consideration when making treatment decisions.
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.
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.