Browsing by Author "Kanyilmaz, Gul"

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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.
Investigation of the Effect of Bolus on Skin Dose in Breast Cancer Treatment With Tomotherapy and Linac Radiotherapy Devices
(Pergamon-elsevier Science Ltd, 2024) Gul, Osman Vefa; Demir, Hikmettin; Basaran, Hamit; Kanyilmaz, Gul
In postmastectomy radiation therapy (PMRT), it is important that the chest wall skin is included in the target volume and receives an adequate dose. This study aims to investigate the effect of bolus on skin dose in breast cancer treatment with Tomotherapy and LINAC radiotherapy devices and to examine the accuracy of the surface dose calculated by treatment planning system (TPS) with thermoluminescence dosimetry (TLD). Female Alderson Rando Phantom's chest wall is virtually divided into 9 regions. Computed tomography (CT) images of the phantom were obtained with a section thickness of 3 mm. Two plans, with and without bolus, were created for each of the helical tomotherapy (HT), intensity -modulated radiotherapy (IMRT) and field -in -field (FiF) techniques. A bolus thickness of 0.5 cm was used for all bolus plans. Doses calculated from TPSs were obtained for 88 predetermined points on the chest wall. After irradiation, doses measured with TLDs were obtained. The effect of bolus use on the chest wall surface was examined. The increase in surface dose due to bolus use was 50.35%, 55.35% and 68.56% for HT, IMRT and FiF techniques in TPS, respectively. This increase in TLD measurements was 58.18%, 30.90% and 46.31% for HT, IMRT and FiF techniques, respectively. The best agreement between TPS and TLD doses for bolus and non -bolus plans was found in the HT technique. The difference between TPS and TLD doses decreased within the three treatment techniques due to bolus use. Since the chest wall skin cannot receive the required dose in IMRT and FiF techniques, bolus use is recommended until acute skin reactions occur. There is no need to use a bolus for the HT technique.
Investigation of the Effect of Calibration Curves Obtained From Different Computed Tomography Devices on the Dose Distribution of Tomotherapy Plans
(Wolters Kluwer Medknow Publications, 2024) Demir, Hikmettin; Gul, Osman Vefa; Kanyilmaz, Gul
Purpose: This study investigated the effect of Hounsfield units (HU)-relative electron density (RED) calibration curves obtained with devices from three different Computed Tomography (CT) manufacturers on dose distribution in Accuray Precision planning of patients with lung cancer. Methods: All CT data required for treatment planning system (TPS) were obtained using the Tomotherapy "cheese" phantom. HU RED calibration curves were created with images obtained from Siemens Somatom, GE Optima, and Toshiba Aquilion devices. The obtained calibration curve was extrapolated. CT images of lung cancer patients were acquired on a single device and treatment plans were created. The existing plans were recalculated using three calibration curves and the effect of the HU RED calibration curve on dose distribution was analyzed. Results: The results showed that different CTs did not produce significant dose differences in organ doses and PTV for Accuray TPS. Conclusions: Based on clinical judgment, images from different CT devices can be used in treatment planning.